Knowledge-Encyclopedia

40,000 miles (65,000 km)—the length of the underwater 55 million years ago, the Indian and Asian plates 49
mountain chains formed by mid-ocean ridges. crashed together, creating the Himalayas.

0.75 in (2cm) per year—the The Challenger Deep
speed of seafloor spreading This is the deepest
in the north Atlantic Ocean. known point on

Continental plate 2 Earth, at 35,800 ft
The Eurasian plate is (10,911 m) below
85 percent land, with sea level.
22 only 15 percent water.
14
29 3

29 22 25 1
13 27
17
10 13 12
4

10 32
24 19 36

5 11 37 38 28
5 31 26

23

30

7

Fresh break 6
This new rift is causing the
African plate to slowly split down Controversial boundary
the middle, creating two new Scientists disagree on
plates—Nubian and Somalian. whether the Indian and
Australian plates are separate
Plate movement Ridge —some think they are a huge,
single, Indo-Australian plate.
Earthquakes
Plate
movement

Transform Magma
When plates slide past each other, they create a transform
boundary. Movement at these plate edges is not smooth and Divergent
gradual—it is very jerky, and earthquakes occur when a sudden Where plates pull apart, they create a divergent boundary. When
shift releases huge amounts of energy. Volcanoes are rare at this happens under oceans, rock from the mantle is drawn up into
these boundaries, because little or no magma is created. the gap and some of it melts as it rises, creating new oceanic
crust. As new crust is formed, other parts of crust are destroyed
at convergent boundaries—so Earth stays the same size.

50 earth TECTONIC EARTH

Volcanoes 75 percent of the world’s
active volcanoes
Where molten rock erupts from an opening on are underwater.
Earth’s surface, volcanoes develop. Most of them
form near the edges of tectonic plates. Lava flow
Some volcanic
Molten rock called magma is formed in a few places deep in eruptions produce
Earth’s crust or even in the mantle. If magma reaches the surface runny flows of lava
it is called lava. Large volcanoes called stratovolcanoes are built instead of explosions
by a series of eruptions, with each one adding a layer of solidified with ash clouds. The
lava and ash on top of the last. Volcanoes are classified as active, lava travels steadily
dormant, or extinct, based on how often they erupt. An active downhill away from
volcano is one that is known to have erupted in recent history. the volcano, usually
A volcano that has not erupted recently but might erupt again moving at a speed
is dormant. A volcano that has stopped erupting altogether is slightly slower than
extinct. Some small volcanoes erupt just once, while a large a running person.
volcano can erupt thousands of times over its lifetime.

Mud pool Farmland Crater lake Fissure
Hot steam and other Ash from volcanoes Rainwater can fill old A crack that
gases escaping near sometimes
a volcano can can make the soil volcanic craters to leaks lava.
produce mud pools nearby very fertile. make new lakes.
at the surface. They
are not boiling—the
bubbles are formed
by escaping gases,
which can be
very smelly.

Maar
A crater formed
by an explosion,
caused by magma
interacting with
water in the ground.

Volcanic eruption

Magma works its way through solid rock and up
toward the Earth’s surface. As it rises, gas bubbles in
the magma grow, increasing its speed until it erupts to
the surface. The violent expansion of these gas bubbles
can shatter the magma, shooting it out explosively as ash
or bigger lumps called bombs. If there is not an explosion,
the magma flows down the side of the volcano in a molten
stream called a lava flow.

60 The approximate number of volcanoes The ash cloud from a large volcanic eruption 51
that erupt in an average year. can be up to 40 miles (60 kilometers) high.

Ash cloud Types of volcanoes
Explosive eruptions create clouds
of sand-sized rock particles, which The size and shape of a volcano are determined by several factors: the
eventually fall to the ground. type of magma that erupts from it; the amount of magma that erupts;
and whether it produces explosive or non-explosive eruptions.
Main vent
The site of most of a Magma Vent Gentle slope Ash Vent Magma
volcano’s eruptions. of basaltic Lava
lava flow Branch
Main conduit pipe
The “pipe” through which
magma rises to reach the vent. Shield volcano Stratovolcano
The biggest but most gently The steepest large volcano,
Lava bomb sloping type. Formed mostly formed of alternating layers
A lump of rock thrown out by runny lava called basalt. of ash and lava.
by an explosive eruption.
Old cone Caldera Convex slope Magma
Pyroclastic flow Ash from thick,
A fast, dangerous flow New cone fast-cooling
of hot gas, ash, and rocks. Magma lava

Secondary vent Caldera Cinder cone
Small hole through The remains of a stratovolcano A small, steep mound that
which magma escapes. after a super-eruption empties grows where very sticky
most of its magma chamber. lava has erupted.
Secondary conduit
A branch off from
the main conduit.

Fumarole
Vent in the ground from which hot
gas and steam escape—often sulfur-
rich and very smelly.

Geyser
A jet of water driven
into the sky by
expanding steam.

Laccolith
A pocket of magma
that has forced the
rock around it to move
and make space for it.

Magma chamber Dike
Magma collects under an A vertical
active volcano, sometimes over magma seam.
an area many miles wide.
Sill
A horizontal seam of
magma, usually between
layers of bedrock.

Extinct conduit
The position of the active
conduit may change during
a volcano’s lifetime.

52 earth TECTONIC EARTH 30 The typical number of small earthquakes that
occur in southern California every day.

Earthquakes Waves in both directions 2 Wave origination
Waves spread out in opposite At the sea surface, the
A natural part of our planet’s workings, directions from a line in the sea sudden upthrust of a mass
earthquakes can be terrifying and destructive surface roughly parallel to the of water from below sets off
events. Some trigger powerful ocean waves a series of high-energy waves.
called tsunamis. rupture line on the seafloor. These start traveling over

Earth’s outer shell is made up of huge slabs Uplift the sea surface at a speed
called tectonic plates. These plates are constantly A block of seafloor of over 500 mph
moving, and push past each other with hard, jerky (800 kph).
movements. In some places, the opposing masses suddenly shoots
of rock become locked together by friction. In these up several feet.
periods, there is a gradual buildup of strain in the Elsewhere, other
locked-up area. Eventually, the pressure becomes so blocks may sink.
high that there is a sudden shift between the blocks
of rock, or a massive break, usually on or near lines
on the Earth’s surface called faults. As this happens,
energy is released in the form of powerful shock
waves, or vibrations, causing an earthquake.
When an earthquake happens under the
seafloor, it can create a tsunami.

How a tsunami happens Shock waves
These powerful
Many types of events can cause vibrations spread
tsunamis, including big volcanic
eruptions near or in the sea, out from the
landslides into the ocean, and even earthquake in
asteroid impacts. However, the most all directions.
common cause is a huge earthquake
under the seafloor, usually where 1 Seafloor rupture
the edge of one tectonic plate rises A large rupture below the
above another. seafloor causes an earthquake.
At the same time, a huge block
Energy waves of seabed is suddenly thrust Epicenter
Earthquakes produce upward. This in turn pushes up A spot on the seafloor
massive waves, which the seawater above, triggering a above the point in
can produce shaking, tsunami wave at the ocean surface. Earth’s interior where
up-and-down movements, the rupture started.

and loud noises. Even waves
Out at sea, tsunami
Inside a fault waves are evenly spaced
Faults at the boundaries at distances of up to
of tectonic plates are 120 miles (200 km).
prone to earthquakes.
Here, two plates move Seawater movements
past each other in As each wave passes,
opposite directions.
Occasionally, the there is a circular
movement becomes movement of
stuck and stress builds
up between the plates. seawater under it.
Eventually, the buildup
of stress causes a sudden Epicenter Wave height increase
shift or rupture, releasing The point on Earth’s A tsunami wave
vast amounts of energy. surface that is
directly above the grows higher as the
Fault line quake’s focus point. seafloor under it
A line at Earth’s slopes upward
toward the shore.
surface, which
marks movement Plate movement
These plates are moving past
between plates. each other side by side, but in
Focus some cases one plate moves
underneath another.
The spot in Earth’s interior
where the quake-producing

rupture begins.

The largest earthquake ever recorded occurred off the 0.3 in (1 cm)—the distance that the whole planet vibrates back 53
coast of Chile in 1960. It caused a devastating tsunami. and forth in space during the very largest earthquakes.

Shock waves Epicenter of P-waves Living on the edge
earthquake S-waves
Earthquakes produce Some countries are more affected by earthquakes than others,
two types of shock NO P-WAVES because they sit on the boundaries between tectonic plates. This
waves, called P and map shows the ten countries with most earthquake fatalities.
S waves, which travel
Low-height through parts of ITALY TURKEY JAPAN
waves Earth’s interior. IRAN
In the open Scientists can CHINA
ocean, each work out where PAKISTAN INDIA
wave has a and when a quake
low amplitude happened by NO S-WAVES HAITI INDONESIA
(height) and may detecting these PERU
pass unnoticed. waves as they arrive
back at the surface.

P-waves change NO P-WAVES
direction slightly as

they cross layers

3 Amplification 1,000 miles
When a tsunami wave approaches a
shore, it slows down and its height increases. The length of the rupture under
the seafloor that caused the 2004
The upward-sloping seabed creates a resistance Indian Ocean tsunami.
to the water movement—it pushes the
water so that the wave is
amplified (gets bigger).

Crest of wave Sea drawback
The top of a large Sometimes water is drawn
tsunami wave away from the shore a
usually foams few minutes before a
as it approaches tsunami wave arrives.
the shore.

Sea becomes
shallower

As the seabed
shelves upward, it

also slows the
approaching wave.

4 Inundation Buildings in danger
When a tsunami wave hits a Few buildings can survive
shore, it doesn’t usually break and the onslaught of a large
collapse. Instead, it continues to surge tsunami wave—many are
forward for a considerable distance, destroyed or swept away.
flooding the whole coast. The powerful
rush of water can smash buildings and
carry cars and people away.

54

EARTH’S ENERGY
RESOURCES
Human life requires energy in the form of light, heat, and food.
Earth contains many useful and essential natural resources, Earth’s energy comes from a variety of sources but mostly
which have been used heavily by humans in recent centuries. from the heat of the Sun and the Earth’s hot interior. This is
These resources include water and food, fuel and building a lot of heat, but capturing, storing, and transporting enough
materials, and the means to make more complex things like of this energy to meet all our needs is difficult and requires
metals and plastics. Many resources have a limited supply, complicated and expensive technology.
and using them has an impact on the environment.
Fossil fuels Ocean
ROCKS AND MINERALS
Fuels such as coal, oil, gas and 1 500–250 MILLION YEARS AGO
Over the more than four billion years of Earth’s development, thousands peat have long been used to heat When ocean animals and microbes
of different minerals have formed and combined into hundreds of rock homes and power machinery. died, their remains drifted down to
types. Humans have found many uses for these rocks and minerals, Earth’s fossil fuels took hundreds the ocean floor, and were covered
from building materials to the manufacture of metals. However, some of millions of years to form, but with sand and sediment.
of the most useful and valuable minerals are rare. Mining and quarrying a significant portion of them have
them is often dangerous and dirty. been burned up in just a hundred
years. Fossil fuels are formed
as time, pressure, and heat
transform organic plant
and animal remains into
hydrocarbons—oil and gas.

Rocks Minerals Ocean Sand, silt, and rock
Silt and sand Oil and gas deposits
Humans have used naturally occurring Earth has thousands of naturally
rocks for thousands of years, occurring minerals. Many of these, Plant and animal remains
originally as tools and then for many such as metal ores, sulfur, and mica,
other purposes, such as the building are used in industry. Other examples 2 250–0.6 MILLION YEARS AGO 3 TODAY
of houses, factories, and roads. include gold, silver, and quartz. The plant and animal remains Oil and gas deposits are buried
became buried, deep under the ocean. deep beneath a layer of sand, silt, and
Over time, heat and pressure turned rock. Oil rigs drill through this layer in
the remains into oil and gas. order to pump out the oil beneath.

Nuclear energy

This energy is produced by the strong force that holds
protons and neutrons together inside atomic nuclei.
Nuclear energy can be harnessed, and produces low
carbon emissions compared to fossil fuels. However,
disadvantages include the risk of releasing radiation.

Rocky landscape Mineral building blocks Renewable energy Solar
Much of the world around us is made up Rocks are made up of natural, nonliving Light energy created
of rocks. To extract rock, heavy machinery substances called minerals. Most rocks There are alternative energy from the Sun can be
is used, cutting deep into the ground. contains several types of minerals. sources to fossil fuels, which are captured and turned
more sustainable and better for into electricity using
Gemstones EMERALD STEP CUSHION the environment. solar panels.
SQUARE PEAR SCISSORS
When minerals are cut and polished, Wind Tidal
they are known as gems. One useful Wind turbines allow The movement of
gem is diamond, famous for its us to harness the water created by the
hardness and ability to cut through power of wind. rise and fall of tides
most other materials. Some other Turbines work best can be harnessed to
gems have practical uses, but most on high ground. generate electricity.
are valued for their beauty and rarity.
Gems can be cut into many different Geothermal Hydroelectric
shapes and are typically used in Earth’s internal heat The movement
jewelry or other decorative objects. comes close to the of water through
surface in volcanic turbines in dams
Cut gems OVAL ROUND MIXED regions and can be can be used to
Gems can be cut into many different BRILLIANT BRILLIANT used to heat water. create power.
shapes. When cut correctly, gemstones
reflect light in many directions, making Biofuels Wood
them glitter. Fuels produced from Burning wood for
organic matter such heat and cooking
as plants, fats, and is the most ancient
waste are called form of energy
biofuels. supply.

55

AGRICULTURE Forestry

Growing food plants and looking after Forests provide habitats and food for
animals that will be eaten is called most of Earth’s land-based wildlife,
agriculture. Today, the global population and help control global warming by
of around seven billion people largely removing carbon dioxide from the
relies on a few cereal crops to provide atmosphere. However, forests are also
its essential foods. These crops include in danger—they are being cut down
corn, wheat, rice, potatoes, cassava, to supply fuel and lumber for building.
soybeans, and sweet potatoes. Protein
from livestock such as fish, cattle, pigs, Well-managed forest
and poultry makes up less than 20 Forests can be managed in a way that
percent of total global food. lets people harvest their produce, such
as lumber, without destroying them.

Farming Russia Key Rice MORE THAN
China Cattle Sheep
Farming began 10,000 years ago, in Coffee Soybeans HALF THE
the Middle East. The first farmers India Pigs Tea
grew cereal crops, like wheat, and Australia Corn Wheat WORLD’S
reared animals for their meat and Oats Milk
milk. Modern agriculture has Potatoes POPULATION RELIES
moved on a lot since then. New
machine-based techniques let US Feeding the world ON THREE
farmers produce much bigger Food is produced all over
yields from their land. Other Brazil the world, both for local GRAINS FOR
innovations include irrigation, consumption and for export. THEIR BASIC
pesticides, new plants, new animal This map shows the top FOOD NEEDS
breeds, and global transport— producers of each crop or
farmers can now send their type of livestock. —WHEAT,
produce all over the world.
CORN,

AND RICE.

Fishing LINE FISHING NET FISHING TRAWLING
Using baited hooks attached to long lines Net fishing is an ancient method, but its Trawling is a form of net fishing where the
Fish are one of the most nutritious is a very cheap way of fishing. However, modern form is on an industrial scale, using net is dragged through the water or along
supplies of protein and have been animals such as turtles and seabirds can be large synthetic nets that can catch huge the seabed. It can cause damage to the
eaten for thousands of years. accidentally killed by this method. volumes of fish at one time. seabed and catches fish of all size and types.
Modern fishing techniques allow
large quantities of wild fish to be
harvested from the world’s seas and
oceans. Although international limits
have been introduced, many popular
fish species are now endangered.
One solution to overfishing is to
rear fish for human consumption
in fish farms.

SUSTAINABILITY Human impact LANDFILL SITE RECYCLING CENTER

Earth’s natural resources Population growth means that we are
are limited. If demand for using up more and more of the Earth’s
essential resources keeps resources, changing the landscape,
increasing, they will become and damaging the environment
rare and expensive. To around us. One way to reduce the
sustain life as we know it, negative impact people have on the
we must make sure that our environment is to make sure that as
resources do not run out. much garbage as possible is recycled,
instead of being dumped in a landfill.

Pollution Japan India Russia United States China
1,375 1,425 1,878 6,430 polluting tons 6,733 polluting tons
All over the world, factories, power plants, polluting polluting polluting
farms, businesses, and homes produce huge tons tons tons
amounts of pollution by releasing chemicals
and other substances that pollute, or dirty, the
natural environment. As people’s use of energy
and other resources grows, Earth is becoming
more polluted.

The effect of industry
Different countries produce different amounts of
pollution. These are the world’s top five polluters.

56 earth EARTH’S RESOURCES 4 billion—the age in years of the oldest
known rock on Earth, a Canadian gneiss.
Rocks Extrusion
The escape of magma Glacial erosion
A rock is a hard natural object made of mineral grains from a volcano, in the When a glacier moves, it transports
(crystals), held together in a compact structure. There are form of lava and ash.
hundreds of different kinds of rock, but they are grouped rocks from under and around it.
into three main types—igneous, sedimentary, and Volcano
metamorphic—depending on how they were formed. A typical volcano
consists of many
Igneous Sedimentary Metamorphic layers of solidified
These form when These form when These rocks form
hot liquid rock, particles from other, when older rocks lava, with some
called magma or older rocks are are changed by ash and cinders.
lava, cools down compressed and heat and pressure.
and solidifies. stick together. Igneous rock
Rock that forms

when magma
cools down

and solidifies.

GRANITE SANDSTONE GNEISS Crystallization
When magma cools
Minerals
inside the Earth it
Rocks are made up of minerals. There are thousands of solidifies slowly,
minerals, but only around 30 are found at Earth’s surface.
Most minerals are crystals—their atoms are arranged in regular forming rocks with
patterns, giving them simple geometric shapes. Each mineral large crystals, such
has its own chemical composition and physical properties.
as granite.
Native elements Compounds
These minerals each contain These minerals contain two Magma
a single chemical element, or more chemical elements. Hot liquid rock
such as sulfur, carbon, or For example, Fluorite contains
a metal such as copper. calcium and fluorine. that contains
dissolved gas.

Intrusion
A mass of magma

inside the Earth.

BORNITE Melting
When rock is subducted,
SULFUR
water escapes from it.
COPPER FLUORITE Combined with heat and

pressure, this makes Metamorphic rock
nearby rock melt. Heat and pressure deep

Measuring hardness in the Earth can make Uplift
Minerals can be soft, like gypsum, or very hard, like diamond. any rock change into a Upward movement
Different scales are used to express hardness. “Mohs scale” is
based on comparing the hardness of ten minerals, while different type, called of rock masses is
“absolute” hardness is based on precise laboratory testing. metamorphic rock. called uplift.

DIAMOND 1,600 Subducted rock
1,400 Formerly seafloor, the
1,200 ABSOLUTE HARDNESS SCALE The rock cycle
1,000 rock at the top of a
800 Rocks transform from one type into subducting plate has a
600 another in an endless cycle. Many factors
400 contribute to this process, both on the high water content.
200 Earth’s surface and in its interior. On
TALC the surface, rock is broken down by
GYPSUM weathering, and glaciers, rivers, and winds
CALCITE erode rocks by carrying particles of them
FLUORITE away. Sediment made of tiny particles of
rock and mud forms in places like lake
APATITE bottoms, coasts, and seabeds. Inside the
ORTHOCLASE Earth, heat, pressure, and melting change
QUARTZ sedimentary and igneous rock into
metamorphic rock, and volcanoes are
TOPAZ formed that create new igneous rock.
CORUNDUM

1 2 3 4 5 6 7 8 9 10
MOHS HARDNESS SCALE

1,500 times—the increase in pressure above atmospheric 4,900 The number of minerals 57
pressure needed to create a new metamorphic rock. identified on Earth so far.

Glacial deposition Precipitation Rocks and minerals
At its end, a glacier Snow and rain feed
dumps rock fragments glaciers and streams, Our planet is mostly made of solid rock. Rock is what
in piles called moraines. which erode rocks. gives Earth its features—mountains, canyons, and plains.
Minerals are the building blocks of every type of rock.

Weathering Most of Earth’s rocks are hidden under a layer of soil and
Rain, wind, frost, chemicals, vegetation, but in some places they are visible at the surface,
heat, and living things all in landscape features such as mountains and canyons. Many
break down rocks. different types of rock have developed over billions of years,
through a variety of processes. These include volcanic activity,
Transport which creates rocks at or near the surface, the formation of
Streams and winds sediments in places like the seafloor, and changes in form—
carry particles away called metamorphism—brought about by heat and pressure
from weathered rock. deep within our planet. These processes are linked in a
never-ending cycle, known as the rock cycle.

River erosion Coastal deposition Marine sedimentation
Rivers contribute Rock particles are Tiny rock particles
greatly to the removal transported by river, carried into the sea by
of rock fragments then settle as sand, mud, rivers slowly settle at
created by weathering. or pebbles on the coast. the bottom of the sea.

Sediment
A layer of fine
particles of sand or
silt, deposited on
the seabed or at the
bottom of a lake.

Subduction
When two tectonic
plates move toward
each other, one plate can
be slowly pushed under
the edge of the other.

Sedimentary rock Burial and compaction
A type of rock that forms As new layers of sediment
when pressure binds particles form, deeper layers are
pressed together, creating
of sediment together. solid sedimentary rock.

58

WEATHER

The constantly changing condition of Earth’s atmosphere determines how high up clouds form and whether
creates our weather—clear skies, wind, cloud, rain, and they produce mist, rain, or snow, as well as when
snow. The amount of sunshine we get and how strong it storms occur. When we study the weather, we can
is determines the temperature and pressure in the see predictable seasonal patterns around the world,
atmosphere. The amount of moisture it contains known as climates.

WEATHER SYSTEMS Monsoons INDIA

Patterns of weather depend on the nature of the local air mass Monsoon winds are massive Summer
and pressure system, which can change over the course of a year. seasonal winds that bring In summer, the South Asian monsoon
For example, in the summer, continental land surfaces heat up, heavy summer rain to blows from the Indian Ocean across
making warm, dry air rise. This produces a low pressure weather subtropical regions, such as India, bringing the torrential rains of
system, which draws in more warm air from the surroundings and Southeast Asia and India. In the wet season, which are essential
can cause storms. In winter, continental land surfaces cool, and winter, they bring dry, cooler for the growth of the continent’s
colder, dense air sinks down from the atmosphere above. weather. Monsoon winds are staple food crops.
strongest in Asia, but they
Pressure fronts Cold front also occur in West Africa,
When cold air pushes into warm air, it northern Australia, and parts
A pressure front divides two forms a cold front, and the warm air is of North and South America.
different air masses. Air masses forced to rise up quickly, creating a steep Monsoon winds change
with differing moisture content, bank of storm clouds with heavy rain. direction between summer
density, temperature, and pressure and winter.
do not mix easily, and the front Warm front
between them is often marked by At a warm front, cold air is replaced INDIA
rising banks of clouds. For example, by warm air, which slowly rises up a
a low pressure air mass with warm shallow slope of cold air, forming clouds
air will rise up above a high followed by rain as the air cools.
pressure air mass with cold air. Any
moisture carried by the warm air
will condense as the air cools,
forming clouds and possibly rain.

Occluded front Stationary front Winter
An occluded front forms when fast- A stationary front forms between two In winter, the South Asian monsoon
moving cold air overtakes a slower- air masses that are similar, and does not reverses, bringing the warm dry
moving warm front, lifting the warm air move much. It can last for several days winds and fine weather of the dry
mass up and causing prolonged rain. and often creates prolonged rain. season across the Indian continent
and out into the Indian Ocean.
Lines called
isobars join WEATHER FRONTS ARE BOUNDARIES
points with
the same BETWEEN AIR MASSES
atmospheric
pressure OF DIFFERENT TEMPERATURES,

An area MOISTURE, AND PRESSURE.
with low
atmospheric Hurricanes
pressure is
called a A hurricane is a huge, rotating tropical storm
depression with high winds and very heavy rain. These
storms start from a cluster of thunderstorms,
Occluded which develop over warm tropical seawater
front in late summer, then merge together into a
larger, spiral hurricane. Their intense low
Cold front pressure draws in warm, moist winds, which
spiral upward as they spin faster. The
Warm front rapidly rising air then cools, forming
towering storm clouds and torrential rains.
Weather map When they reach land, hurricanes cause
These maps show the main weather of a region. Air pressure is shown flooding and are highly destructive.
by black lines called isobars, which link areas with equal air pressure.
Weather fronts on the map show where temperatures will rise or fall. The view from above
A satellite view of a hurricane from
above shows its spiral shape and a clear
central eye.

59

PRECIPITATION Cloud formation 1MOISTURE RISES 2VAPOR CONDENSES 3CLOUDS RISE
Hot sunlight makes As the vapor rises As water droplets
Any kind of falling moisture is When the Sun shines on ponds moisture from the ground and cools, it condenses form clouds, they release
called precipitation. Precipitation and lakes, some of the water they or sea surface rise into to form visible clouds heat into the surrounding
varies widely, from the tiny droplets hold evaporates into the warm the air as water vapor. of tiny water droplets. air, lifting the cloud up.
of clouds or fog to larger drops of air. This warm water vapor then
rain, hail, or snow. Whether water rises up and away from Earth’s
falls from a cloud as rain or snow surface. As the air rises, it cools.
depends on how cold the air Because cold air cannot hold as
temperature is. much moisture as warm air, the
water vapor condenses, and
Types of precipitation forms clouds. Clouds that form
very high in the atmosphere,
Different types of precipitation can fall above 16,500 ft (5,000 m), are
from the sky or rise from the ground, made of ice crystals rather
depending on the temperature conditions. than water vapor.

Rain Cloud types Cloud names
Clouds are made up of Clouds are named according to
tiny droplets of water. Rain falls There are three main groups of clouds, though they each have their shape, size, and how high
when these droplets become too many variations. Cumulus form in bulging heaps, stratus are up they form in the atmosphere.
heavy to float in the air. layered, and cirrus are wispy or fibrous. A cloud’s shape reflects
the amount of moisture in the atmosphere and how it moves.
Snow
Snowflakes form when water CIRRUS CIRROCUMULUS 33,000 FT
droplets freeze into crystals, which CIRROSTRATUS 10,000 M
then stick together as they fall
through very cold air. ALTOCUMULUS 26,000 FT
8,000 M
Sleet ALTOSTRATUS
Sleet is a mixture of snow and rain. 19,500 FT
It forms when rain begins to freeze STRATOCUMULUS CUMULUS NIMBOSTRATUS CUMULONIMBUS 6,000 M
or when snow begins to melt in air
that is above freezing. STRATUS 13,000 FT
4,000 M
Hail
Hailstones are ice pellets that grow 6,500 FT
from ice crystals in freezing storm 2,000 M
clouds. The taller the cloud, the
bigger the hailstones.

Fog
Fog forms near ground level, when
warm, moisture-laden air is cooled
by contact with a cold ground or
sea surface.

WIND Tornadoes Thunderstorms

Winds are common in the Earth’s atmosphere. Tornadoes are rotating columns of air that Thunderstorms form in
They vary in scale and intensity from gentle can be violently destructive. Most have large cumulonimbus clouds.
breezes to violent storms like tornadoes, and wind speeds of less than 120 mph (200 They carry water vapor
can be daily or seasonal. kph), but they can reach 300 mph (480 high into the atmosphere,
kph). Tornadoes are characterized by a where it condenses into
central spinning, funnel-shaped column of hail and ice.
air, which extends from the clouds to the
What is wind? BEAUFORT WIND SCALE ground. They have the power to destroy 1 STEADY SPIN
0 CALM crops and buildings. Tornado formation Rising warm air
Wind is the movement 1 LIGHT AIR is associated with summer storms, starts to rotate, and
of air from an area of 2 LIGHT BREEZE especially in the US. the base of the cloud
high pressure to an area 3 GENTLE BREEZE extends down.
of low pressure. The 4 MODERATE BREEZE
greater the difference 5 FRESH BREEZE 2 FUNNEL GROWS 3 IN PROGRESS 4 COLUMN DIES Lightning
between the areas of 6 STRONG BREEZE Funnel extends Spinning column Eventually, the The movement of hail and ice
pressure, the faster the 7 NEAR GALE down to the ground, of air can be several column narrows, and in a thundercloud causes an
wind moves. Wind 8 GALE draws in hot air, and miles wide and rises back up into electric charge to build up,
speed is measured 9 STRONG GALE begins to spin faster. very destructive. the cloud. which zaps down as lightning.
using the Beaufort 10 STORM
scale, which ranges 11 VIOLENT STORM
from 0 to 12. At 12 HURRICANE
12 on the scale,
hurricane wind speeds
can reach 300 mph
(480 kph).

60 earth WEATHER Over its life, a hurricane uses as much 2 in (50 mm) per hour—the rainfall
energy as 10,000 nuclear bombs. produced by a hurricane.

Hurricanes Airflows
Warm air from the top of the
Earth’s most destructive storms occur in tropical regions, above hurricane spirals out from the
warm waters. They produce torrential rains and extremely fast eye, then cools and descends
winds, which can exceed 155 mph (248 kph).
as the pressure falls.
Hurricanes form in late summer, above warm waters. They begin when
clusters of thunderstorms whirl together, evolving into complex structures Outflow cloud shield
with vast spiral bands of rain. The low pressure created by these The top of the hurricane is
structures draws warm, moist air across the ocean. This air then rises, a circular cloud roof of air,
releasing torrential rains and heat energy. Wind speeds above 74 mph
(120 kph) combine with the low pressure to create storm surges of flowing out from the eye.
seawater many feet high that flood over coastal regions as the hurricane
nears land. When hurricanes pass over land, they are no longer fed by
heat from the warm ocean water, and they soon lose force—but often not
before they inflict massive damage with their heavy winds, torrential
rains, and gigantic waves.

Naming the storm ATLANTIC Tropical Moving out
OCEAN cyclone Rising pressure
Hurricanes have the
same structure and pushes the
evolve in the same upper clouds
way wherever they
are. However, how outward.
they are named
depends on the part INDIAN PACIFIC
of the world where OCEAN OCEAN
they occur. This map
shows what they are Hurricane Typhoon 3 Tropical storm
called in different A tropical storm forms
parts of the world. when surface winds reach
between 38 and 74 mph
(61–120 kph). The storm
becomes increasingly
organized, with clouds rising
over 3 miles (5 km) high, and
producing torrential rain.

1 Tropical disturbance 2 Tropical depression
In areas with high Where tropical storms
humidity and light winds, merge together, the rising air
tropical water can become mass produces a low pressure
heated. This produces clusters disturbance known as a
of thunderstorms, which depression. The low pressure
release rain and heat, rising draws warm, moist air in
many miles above the surface as surface winds, which
of the ocean. begin to rotate.

Winds begin to Top of storm
spin the clouds spreads outward

Warm, Spiraling winds
moist air get faster

Towering Destructive hurricane-force
thunderstorm clouds winds can extend up to 100
miles (60 km) away from the

eye of the storm.

Large hurricanes can be over 61
990 miles (600 km) wide.

Eye

A calm, cloud-free area

of sinking air and light

winds. The eye is usually

between 20 and 30

Spiral rain bands miles (32–48 km) wide.

Rising warm air creates

long, curved bands of Eye wall
thunderstorms inside A ring of destructive
the hurricane. thunderstorms and rain

Surface winds bands around the eye.

Low pressure at the water’s surface

creates warm winds that move in

a counterclockwise direction. These

winds pick up speed toward the eye. Ascending warm, moist air

Air is heated by warm

ocean waters, picks up

4 Hurricane How a hurricane forms water, and rises upward.
As storm clouds and
winds reach speeds above Hurricanes are the result of interaction Descending cool, dry air
120 kph (74 mph), they are between heat, water, and wind. As clouds Cool, dry air sinks down
drawn into a spiral form. produce rain, they release heat and rise to
Rising warm air in the around 5 miles (8 km) above sea level. Here,
storm clouds is replaced increasing pressure pushes the uppermost

by descending cooler air clouds outward, lowering the pressure at toward the ocean’s surface.

and light winds within a sea level. This causes wind speeds to
central eye. increase and draw in even more heat

and moisture from the ocean surface.

62 earth WEATHER 20 percent of the world’s fresh water is
contained in Lake Baikal, in Russia.

The water cycle

Earth’s water is always on the move, Snow on mountains Snowfall Transpiration
traveling endlessly around our planet in Where there are Cold air freezes any Plants release
a process known as the water cycle. Without high mountains, moisture it carries, moisture into
water, life on Earth would not be possible. forming snowflakes.
moisture in the air the air.
Earth’s water is stored in many forms, including falls as snow. Rainfall
oceans, rivers, lakes, glaciers, and groundwater. This When moisture-carrying
water moves around constantly. The water cycle clouds cool, they release
begins when the Sun’s heat makes water evaporate water as rain.
into the atmosphere, where it becomes clouds,
dew, or fog. This water falls back down to Earth’s Snow melt
surface as rain or snow, then streams and rivers When air temperatures
carry it to lakes or the sea, where it eventually rise, snow melts, releasing
evaporates and the whole cycle begins again. fresh water.

The presence of water on the Earth is what
gives our planet its wet and warm
atmosphere. The atmosphere protects the
Earth from the Sun’s radiation, which has
allowed the evolution and survival of life on
Earth. Earth is thought to be the only planet
in the Universe to support life.

Water on the move Porous rock Freshwater lake Underground water flow
Cracks and holes in Water collects in Water can flow downhill
All water on Earth is included rocks allow them to hollows in the ground. underground as well as
in the constant circulation of be filled with water. above ground.
the water cycle. Even the snow
on mountain peaks or in the ice Fault lake Kettle lake
sheets of the Antarctic is a part Movement of A steep-sided
of the cycle—eventually, it will tectonic plates circular lake,
melt and be on the move again. can create long formed when
Underground water is also hollows, which an underground
involved—it flows in a similar fill with water. block of ice melts.
way to rivers, despite being
hidden out of sight. Caldera lake Man-made lake
A circular lake People make
Lake types is created when lakes to generate
rainwater fills hydroelectricity
Lakes are formed when the hole left in a and create
water fills hollows in the volcano’s summit reservoirs of
landscape. Most lakes after an eruption. clean water.
contain fresh water, though
they can also be salty. They
range in size from ponds to
large lakes and even inland
seas. The depression lakes
are formed in various ways
and may be millions
of years old or newly
man-made. Lakes are not
permanent—they can
gradually disappear as layers
of sediment build up in them.

97 percent of the world’s water A drop of water can spend as little as nine days or as The world’s largest river is the Amazon, which holds 63
supply is stored in the oceans. long as 40,000 years moving through the water cycle. around 20 percent of the world’s flowing fresh water.

Forests and plants Cloud movement Clouds carry water inland Condensation
Plants help soil retain Clouds are moved by Winds blow moisture-laden Heated, rising water vapor
moisture but also wind and heat energy. cools and condenses,
release water into clouds inland. forming clouds.
the atmosphere. Evaporation
Heat from the River flow Evaporation from sea
Sun draws moisture Rivers steadily The Sun heats the surface
from the ground transport water of the ocean, so that some
into the air. to the oceans. of the water evaporates
and rises into the air as
water vapor.

Ocean water
Seawater is salty
because it contains
dissolved minerals.

Bedrock Water table Rivers flow into seas
Solid rock that Ground that is Eventually, downhill
occurs below soil saturated with water. flow means rivers
and soft sediment. flow into the oceans.

Rivers Mid-speed flow MOUTH
of water
When rain falls, the Slow-flowing water
water drains from Middle course
high ground to lower Fast-flowing water On lower, flatter ground, Lower course
ground. Small channels rivers begin to slow down. As they reach lower ground,
of water join up, forming SOURCE They develop bends called rivers widen and slow, then
streams and rivers that meanders, and there is an flow into lakes or the ocean.
flow into the sea or fill Upper course increased risk of flooding. Sediment carried by the water
dips in the landscape to Where rivers begin they is left behind as the river slows.
create lakes. The shape are very fast-flowing. The
and character of a river water is full of sand and
varies—they are fast pebbles, which erode and
and narrow at their deepen the stream channel.
source and get steadily
wider and slower
toward the mouth.

64

SHAPING COAST
THE LAND
Coasts are constantly being shaped by nature. Where coasts are
The landscape may look unchangeable, but it has been exposed, the action of powerful ocean currents and waves wears
shaped by the forces of wind and water over millions away the landscape to form cliffs and headlands. On more sheltered
of years. Together, they break down, or erode, rocks coasts, sediments build up to form sandy beaches, dunes, mudflats,
into tiny fragments called sediment, then carry them and salt marshes. Rivers also affect coasts as they lose energy and
away. This is usually a very slow process, but extreme leave behind the sediments they carry when they approach the sea.
events, such as floods and hurricanes, can speed it up.
Coastal erosion

Pounding relentlessly, day after day, waves play a key role in
shaping the coastline. They break against the shore with immense
force, dislodging weak or loose rock material and grinding it into
pebbles. Repeatedly hurled back against the shore by the waves,
the pebbles themselves increase the waves’ erosive action.

Beach Headland

WIND Bay Erosion divides
headland into
You’ve probably had sand blown in your face on the beach, so stacks
you’ll know that winds can be strong enough to pick up dust, grit,
sand, and soil particles. These sediment particles can be carried
over huge distances. Wind erosion and deposition (the laying
down of sediment) typically happen in dry places with little
vegetation to protect the rocks. Characterized by low rainfall, these
environments are known as deserts and often contain sand dunes.

Sand dunes Wind Waves slow down Sediment
as they move into builds up
The more powerful a wind is, the Transverse dunes underwater
further it can carry sediment particles Constant winds carrying lots of sand shallower water
before dropping them to the ground. form rows of dunes with crests that lie Waves hit the
As they roll and bounce on the ground, at right angles to the wind direction. Steady waves headland
these particles create small, wave- The size of waves—and their power—depends on
shaped ripples. These ripples the strength of the wind and how far the waves
sometimes build-up into larger travel before they break on the shore.
formations, called dunes. With
persistent winds, sand dunes can
grow to many feet high and
several miles long.

Wind Wind

Deposition Sediment buildup
Sediments can be washed
Rivers laden with sediment dump their cargo at or blown further along the
river mouths to form wide shallow areas called coasts, into offshore waters,
estuaries. Sea waves and currents wash much of and even on to land, where
the sediment along the coastline. The mud and they form dunes.
sand form beaches, sand dunes, and headlands,
which help to protect the coastline from erosion.

Crescent (barchan) dunes Star dunes River Salt marsh Old Headland Sand moves
Winds of varying strength and sand These dunes form when the wind current coastine along beach
content form crescent-shaped dunes direction constantly changes. They
with “horns” pointing downwind. may grow to a considerable height.

Wind erosion Rocky arch Wind Beach with Sand is moved along Wind
Sand-blasting can create strange shapes sand dunes by wind and currents
Over time, the constant lashing of from rocks, such as this natural arch in the
winds can wear away at exposed Arches National Park in Utah.
rock surfaces. This wind erosion
produces weird-looking and
unstable formations, which
eventually collapse in most cases.
Even very hard rocks may be
slowly shaped and polished by
sand blasting. Barren landscapes
can be created if all the soil in an
area is blown away by the wind.

65

WATER Rain RAINDROPS

The salty waters of the oceans cover Earth’s atmosphere contains ARE ALWAYS
about three-quarters of the Earth’s entire tiny particles of moisture in the
surface. Heat from the Sun evaporates form of clouds, fog, and steam. SMALL—THEY’LL
ocean water, which rises into the Temperature and pressure changes
atmosphere and forms clouds. This cause the moisture to condense SPLIT INTO
airborne moisture eventually falls to into larger, heavier drops, which
the ground as rain. Some rainwater fall back down to Earth as rain, TWO DROPS
soaks into the soil or becomes stored hail, or snow. The impact of
in rocks underground. The rest of the raindrops hitting the ground can IF THEY GROW
water runs off the land to form rivers, move particles of soil or sand.
which return the water to the sea, BIGGER THAN
completing a process that is known Essential water
as the water cycle. Rainwater is vital for life—it 0.25 IN (4 MM).
nourishes all plants and animals
that live on land. Oxbow lakes

Rivers On low-lying land, the course
of a river may bend to form
Water flows down slopes under the influence of gravity. snakelike meanders. If a meander
As a result, Earth’s surface water runs off the land as curves too much, it will eventually
mountain streams, which join to form larger rivers that become completely cut off from
carve out valleys as they flow down toward the sea. the main river. The result is a
The more powerful the flow of the river, the more loose U-shaped body of water known
sediment, such as mud and sand, it can carry. as an oxbow lake.

World’s longest rivers
The Nile is the world’s longest river, stretching for
4,130 miles (6,650 km). The Amazon, although not as
long, carries more water—about one-fifth of all the
river water on Earth.

NILE (AFRICA) Winding river Steady bend
AMAZON (SOUTH AMERICA) Where rivers flow slowly over in river
YANGTZE (ASIA) low-lying land and are not
RIVERS MISSISSIPPI–MISSOURI (NORTH AMERICA) hemmed in by valleys, their
YENISEY–ANGARA (ASIA) channels bend sideways into
curves known as meanders. 1 RIVER WITH MEANDER
LENGTH 2,500 MILES 3,000 MILES 3,500 MILES A slight curve forms in a river’s course
(4,020 KM) (4,830 KM) (5,630 KM) 4,000 MILES as the flowing water erodes the outer bank
(6,440 KM) and deposits sediment on the inner bank.
Over time, this action exaggerates the
Waterfalls Glaciers curve and turns it into a meander.

The ability of a river to erode its valley depends upon Ice is hard and brittle but it can also flow slowly River wears
the hardness of the rock over which it flows. Soft rock when under pressure in moving channels of ice away land
erodes more quickly than hard rock. In places where called glaciers. Glaciers pick up pieces of grit and
the river’s course takes it over both hard and soft rock rock fragments as they move along, which grind
surfaces, the different rates of erosion may gradually over the landscape, carving out a deep valley
lead to the formation of waterfalls. underneath the ice.

Rapids Pool forms at
base of waterfall

2 BEND TIGHTENS
Continuing erosion and deposition
tighten the curve of the meander into a
C-shaped loop. The neck of the meander
gradually gets narrower and narrower.

Old loop of
river gets
cut off

Hard rock Soft rock Softer rock is River
worn away straightens

out

1 RAPIDS 2 WATERFALL Glacier on the move 3 BEND IS CUT OFF
Where a shallow river The river erodes soft rock Vast rivers of ice called glaciers flow The curve grows so tight that the river
under the influence of gravity from cuts through the meander’s neck to follow
flows over a layer of hard rock, on the river bed just beyond high mountains to lower ground. a new, straighter course. Sediment seals the
ends of the old loop, leaving an oxbow lake.
its flow is broken up by rapids the rapids, carving out a

—rocky outcrops that project plunge pool into which the

above the water’s surface. water tumbles freely.

66 earth SHAPING THE LAND 352 miles (563 km)—the length of the world’s longest
cave system—Mammoth Cave System in Kentucky.
Caves
Karst Surface stream
Underground passages and caves Bare limestone-rock
are found in rocky landscapes landscapes produced Column
across the world. They are common by chemical weathering A growing stalactite
in areas with a lot of limestone. are called karst. They can join a stalagmite
feature deep trenches
Cave systems form when acidic water and sharp limestone to form a column.
etches its way through rock. Rainwater pinnacles.
becomes acidic when it takes in carbon Limestone
dioxide from the atmosphere, while Collapsed blocks pavement
groundwater can pick up acids from soil. When rocks are weakened, the An exposed
The water causes existing cracks in the roof of a cave can fall in, leaving rock surface,
rock to widen into passages, which the a pile of rock on the cave floor. crisscrossed
water flows through, creating channels. with cracks.
Over time, the flowing water opens up Sinkhole
passages and caverns, and more rocks A hollow in the
weaken and fall, creating larger caverns. surface that leads
The surfaces of these caverns can
become covered with a variety of underground.
crystalline deposits, which form when
mineral-enriched water evaporates,
leaving behind solid structures called
stalactites and stalagmites.

Stalactite

Stalactite and stalagmite formation Fir cone stalagmite Gour
As mineral-saturated water drips from a cave roof, A mineral dam
it leaves a mineral residue on the roof and on the that forms at the
floor below. Over time, continued dripping creates outflow of a pool.
pointed deposits hanging from the roof (stalactites)
and rising from the floor (stalagmites). Eventually, Bedrock
these can join together to form columns. The rock in which a
cave system develops.
Stalagmite

Inside Earth

The gradual weathering of limestone rock
by acidic water can create incredible cave
systems. Over thousands of years, small
caves steadily grow, creating huge caverns,
while small cracks in the rock become large
tunnels. When these link up, huge interlinked
networks are created, filled with thousands
of stalactites and stalagmites. With the
right safety equipment, these caves can be
exciting environments for people to explore.

Tham Hinboum cave in Laos has the world’s longest navigable 92 ft (28 m)—the length of the world’s longest stalactite, 67
underground river—it is over 4.5 miles (7 km) long. which is in Gruta do Janelao cave in Brazil.

How gorges form LIMESTONE WEAKENS CAVE SYSTEM IS FORMED CAVE ROOF COLLAPSES
Roof weakens
The development of cave Roof blocks fall
systems means large Horizontal Cavern opens to the floor of
amounts of limestone and vertical up as rock is the cave
rock is removed from a cracks form dissolved
landscape. Underground
cavities are enlarged by Water flows through
rock falls and form weakened rock
caves. Eventually, the
caves roofs collapse,
creating sinkholes, which
can then merge to form
larger sunken regions
with steep sides, known
as gorges.

Pothole Jointed limestone Waterfall 1,000
An entrance to The movement of A vertical cascade
a cave system. the Earth creates a of water over a years—the time it takes for
rectangular series blockage in the 1 in3 (16 cm3) of stalactite
of cracks, or joints, Dry cave stream bed. or stalagmite to grow.
in brittle limestone. A cave without
any water in it.

Rock column
A pillar of rock
left when caves
have formed and
then collapsed.

Wet cave Curtain stalactite Underwater cave
A cave with streams Long, thin, hanging A cave system formed
and pools, which may stalactite. below the water level.
fill some passages.

68 earth SHAPING THE LAND 10 percent of Earth’s land is If all glacial ice melted, the worldwide
covered with glacial ice. sea level would rise by 230 ft (70 m).

Accumulation zone Glaciated valley Pyramidal peak
The area where snow A peak where a mountain
turns into glacial ice. As a glacier travels through a valley it
wears away at the landscape, dragging has been eroded by
grit and dirt from the ground and carrying glaciers on all sides.

them along with it. Glaciers are not just a

mass of solid ice—as well as debris, they

are crisscrossed with cracks called

crevasses and channels of meltwater.

Arete

A sharp, steep, rocky

Tributary glacier ridge formed by glacial
Small glacier that erosion of a mountain
flows into a major on two sides.

valley glacier.

Lateral moraine
Rock debris that has
fallen from the sides of
the valley can pile up at
the edge of the glacier
and get carried along.

Terminal moraine
Crescent-shaped

mounds of debris at
the end of the glacier.

Cirque
A shaded
mountainside
hollow where snow
and ice pile up.

Cirque glacier
The first glaciers to

form on shaded
mountainsides. They

grow and feed into
valley glaciers.

Valley glacier
A glacier contained
by high, rocky walls.

Glaciers Medial moraine Meltwater
Debris along the
Glaciers develop when mountain snow builds up into
masses of ice. If there is a slope, the glacier then moves middle of a
steadily downhill, carving its way through the landscape. glacier, formed
when two valley
From the poles to the equator, glaciers develop wherever it is glaciers merge.
cold enough for winter snowfall to survive the summer thaw.
Layers of snow compress into glacial ice and move downhill due Terminus
to the influence of gravity. Glaciers follow existing river valleys The clifflike end of a
and may merge together into much larger ice sheets. glacier, where it stops

Over hundreds of thousands of years, glaciers have a huge flowing and melts.
impact on the landscape around them. Rocky debris becomes
embedded in glaciers, and cuts into the landscape, changing the Meltwater stream
shape of the valleys they move through. This debris is then Meltwater flows away
dumped onto surrounding landscapes wherever the glacier
comes to rest and melts. from the glacier.

In some places, Antarctica’s ice sheet 32 percent of land was covered 69
is more than 2.6 miles (4.2 km) thick. with glacial ice in the last ice age.

Truncated spur After the glacier
A mountain ridge
that has had its end Glaciers leave many signs behind when they have passed
cut off by a glacier. through an area. Rock debris called moraine is left in piles.
Valleys are gouged into deep U-shapes with close vertical
sides, and are often flooded with melt water. Rocks are
scratched by other rocks and debris that is carried along by
the gritty ice, and even huge boulders can be relocated.

Waterfall Hanging valley
A tributary valley, once occupied by
a tributary glacier, whose floor lies 70 percent of Earth’s
high above that of the main valley. fresh water is stored
as glacial ice.
Lateral moraine
A trail of debris along
the side of a valley, left
when a glacier melts.

Drumlin
A mound of glacial debris
that has been molded into
an egg shape.

Floodplain
The flat valley floor
beside a stream that
is periodically flooded.

Tarn
A lake-filled
hollow created by
a cirque glacier.

V-shaped valley Kettle lake
A river valley that Water-filled hollow
has not been formed by the
affected by melting of ice that
glacial erosion. was buried under
glacial deposits.
U-shaped valley
A steep-sided, flat- Erratics
Blocks of rock that have
bottomed valley, been carried away from their
eroded by a glacier. original source by a glacier.

Ribbon lake
A long, narrow lake.

Stream

How glacial Airborne snow Ground snow Granular ice Firn Glacial ice
ice forms Fresh snow falls, Within days, flakes are Within a year, the The grains steadily Firn grains are packed
formed of delicate broken by the weight fragments form get smaller and more together to create
Glacial ice forms six-sided crystals. of new snowfall. round, dense grains. tightly packed. larger ice crystals.
gradually, when fresh
snow is steadily
weighed down by
the accumulation
of newer flakes.
Eventually, this
compression turns light
snow into dense ice
with few air bubbles.

70

EARTH’S OCEAN WATER
OCEANS
Most of Earth’s water is found in its oceans, which cover
The blue waters of Earth’s oceans cover almost three much of the planet’s surface, with an average depth of
quarters of our planet, dominating its surface. The world around 12,240 ft (3,370 m). Deep ocean waters extend
beneath the water’s surface is Earth’s most mysterious from the north and south poles right around the world to
and least explored region. Fifty percent of the world’s the equator. They vary considerably in properties such as
species live in the oceans, which have been home to life saltiness, temperature, pressure, light penetration, and the
since it first evolved, over 4 billion years ago. forms of life they support.

ARCTIC OCEAN

ATLANTIC PACIFIC
OCEAN OCEAN

THE SEAFLOOR PACIFIC INDIAN
OCEAN OCEAN
The ocean floor is just as varied as land. Its features are mainly
created by the movement of the plates that make up Earth’s crust. SOUTHERN
Where plates move apart, ridges open and create new ocean floor. OCEAN
Where plates collide, old rock is pushed into Earth’s interior,
forming deep trenches. Volcanic islands erupt from the ocean
floor and some even rise above sea level. They are surrounded by
deep, flat abyssal plains and covered with fine-grained sediment.

Ocean features Oceans and seas The world’s oceans
Oceans are named
OCEAN TRENCHES HYDROTHERMAL VENTS Earth has five oceans and over 50 individually, but they
Where two of Earth’s tectonic plates The presence of hot rocks beneath seas. Oceans are large expanses of all join up into one
push into each other, one will be forced spreading ocean ridges produces open saltwater. Seas still contain global body of water.
underneath the other in a process called numerous hot springs, known as saltwater, but they are smaller and
subduction. Deep, valleylike trenches hydrothermal vents. The heated partly surrounded by land.
are formed between the plates—some seawater is rich in minerals and
can be almost 6.8 miles (11 km) deep. pours out onto the ocean floor, ARCTIC SOUTHERN Ocean sizes
creating towerlike structures
VOLCANIC ISLANDS called black smokers. These INDIAN Earth’s oceans are very different
The movement of tectonic plates extreme underwater environments sizes. The largest ocean is the
under the ocean causes molten are similar to those in which life PACIFIC Pacific, at 63,784,076 square miles
rock (magma) to bubble upward first formed. (165,200,000 kilometers2), and the
into the water. If there is a lot of ATLANTIC smallest is the Arctic, at 5,428,600
magma then it rises and erupts at ABYSSAL PLAINS square miles (14,060,000 kilometers2).
the surface, forming an arc-shaped The deep ocean floor lies more than
series of island volcanoes. 9,843 ft (3,000 m) below sea level. 75% of Earth’s
It covers 50 percent of the Earth’s surface is
OCEAN RIDGES surface but is the least explored underwater.
These ridges form when two of Earth’s part of the planet. The rugged volcanic
tectonic plates pull apart and magma mountain landscape of the seafloor IF THE OCEAN WATERS WERE
wells up between them, solidifying into is buried beneath fine-grained, muddy
new rock. The system of ocean ridges sediment, which forms a dark, SPREAD OUT EVENLY
extends over 36,780 miles (59,200 km) featureless, intensely cold and
around the globe. inhospitable environment. OVER EARTH’S SURFACE THEY WOULD COVER

Hidden mountain Mount Everest THE ENTIRE SURFACE TO A DEPTH OF
29,028 ft
Measured from its underwater base to (8,848 m) 8,200 FT (2,800 M).
its summit, Mount Kea in Hawaii, is even
taller than Mount Everest.

Mount Kea 13,796 ft (4,205 m) Salty seas
33,476 ft above water
All seawater is salty, but only a
(10,203 m) 19,680 ft (5,998 m) small percentage is actually salt.
below water As well as salt, seawater contains
SEA LEVEL over 86 chemical elements and very
low concentrations of precious
metals such as platinum and gold. 96.5% WATER 3.5% SALT

71

Sunlight and darkness WATER ON THE MOVE LESS THAN

Sunlight cannot shine far through ocean water. Only blue light Ocean water is in constant motion. Wind on 10% OF THE
reaches water below 150 ft (45 m), and below 660 ft (200 m) the water’s surface creates waves. Gravity
there is no light at all. Ocean waters can be divided into zones between the Sun, Moon, and Earth creates OCEANS
depending on how much light reaches them and how cold they tides. Heat from the Sun generates currents
are—the water gets colder as it gets deeper. Each ocean zone around the world, as the heated water rises HAVE BEEN
provides a habitat for different kinds of life. Animals that live to the surface while cold water sinks.
in the deeper zones have special adaptations to survive there. EXPLORED.

SURFACE SHARK Sunlit zone Waves Round and round
HERRING This zone is full of Water particles do
life, including plants Most ocean waves are generated by wind, with wave not move forward with
that use the sunlight height, spacing, and direction depending on how strong waves—they travel in small
to produce energy the wind is and how long it blows. Long-term winds circles or loops.
by photosynthesis. produce giant, widely spaced waves.
Crest
660 FT Path of WAVE LENGTH
(200 M) water Trough

OCTOPUS Twilight zone molecule
It is too dark for plants
JELLYFISH to live here, but there Circles are smaller
is just enough light for in deeper water
3,300 FT animals to hunt by.
(1,000 M)

WHALE Dark zone
The only light here
GULPER EEL 13,100 FT comes from a few Tides
DEEP-SEA CRAB (4,000 M) animals that are able
to emit their own. Regular rises and falls of sea level
ISOPOD around the world are called tides.
Abyssal zone The Moon’s gravity produces two
19,700 FT The animals here must high tide bulges of ocean water, on Low tide
(6,000 M) be able to withstand opposite sides of the globe. Between Tides mean the sea level changes through the day.
the huge pressure these bulges are the low tides. As At high tide these boats would be afloat.
created by the weight Earth rotates, the tides sweep around
of the water above. the globe. As well as this daily cycle,
the weaker pull of the Sun produces
Hadal zone an additional monthly cycle, with a
The ocean gets this variation in the heights of the high
deep in just a handful and low tides.
of trenches. Only two
OCEAN FLOOR CUSK EEL ANGLERFISH people have ever Currents
visited this zone.
Ocean surface water currents are driven by winds that blow
Water temperature from the hot tropics to cooler northern regions. They form Global currents
ocean-wide flows called gyres. Oceans also have deeper There are two sets
Deep ocean water is always cold, but the temperature of currents, which are known as the Great Ocean Conveyor. of currents in Earth’s
surface waters varies greatly. This means that different ocean These deep currents are caused by sunlight heating tropical oceans—surface currents
habitats exist, with tropical coral reefs in warm areas and waters. The warm water flows toward cold polar regions, on top and deep-ocean
cold-loving animals around the north and south poles. where it cools and sinks, forming a deep current that flows currents further down.
back toward the tropics, where it warms and rises again.
Warm
tropical
water

90°F 30°C Permanently Warm surface currents Warm deep-ocean current
70°F 20°C cold water Cold surface currents Cold deep-ocean current
50°F 10°C
30°F 0°C Water surface temperatures
Ocean surface water is warmest around
the equator and the tropics, and coldest
around the north and south poles.

72 earth EARTH’S OCEANS 180 million years—the age of the 36 °F (2°C) The temperature at
oldest rocks on the ocean floor. the bottom of the ocean.

The ocean floor Into the depths

The world beneath the ocean surface is as varied as the Where one tectonic plate dips under another it creates a trench
more familiar one above water, with huge mountains in the seafloor. These are some of the deepest trenches—most
and volcanoes, vast plains, deep canyons and trenches,
and massive ridges that snake across the seafloor. are found around the edges of the Pacific Ocean.

Many seafloor features are the result of melted rock called 20,000 ft
magma rising up from inside Earth. Where tectonic plates 6,000 m
(slabs of Earth’s outer shell) pull apart at a mid-ocean ridge,
the magma solidifies and creates new seafloor. Older plate is 23,000 ft
pushed away from the ridge and eventually may move under 7,000 m
a neighboring plate. This allows more magma to move upward,
creating volcanic islands. Not all seabed features are made 26,000 ft
by magma—submarine canyons are caused by erosion around 8,000 m
the edges of continents, and abyssal fans are created by
submarine currents dropping off the silt they were carrying. 30,000 ft
9,000 m

33,000 ft
10,000 m

36,000 ft
11,000 m
MARIANA
TONGA

PHILIPPINE
KERMADEC
IZU-OGASAWARA

KURIL

Continent Intertidal area Continental shelf Submarine canyon Abyssal fan Guyot
Most land on Due to tides, this area The flooded edge of A deep gorge in Silt carried down a When a volcanic island sinks
Earth is collected is sometimes wet and the continental canyon spreads out beneath the ocean, it
into large masses a continent, which slope, carved by at the bottom as a eventually becomes a flat-
called continents. sometimes dry. was once dry land. ocean currents. fan-shaped deposit. topped seamount, or “guyot.”

Mid-ocean ridge
As two plates pull apart,
magma rises up between them,
then cools and solidifies,
making new tectonic plate.

Continental crust Continental slope Continental rise Underwater plateau Magma
Earth’s outer layer of This steep slope A gently sloping A large, flat-topped mound Melted rock beneath
rock—can be (43 miles region that extends Earth’s surface is called
goes down to about down from the caused by a few million magma. Above Earth’s
100 km) thick in 10,000 ft (3,000 m). continental slope. years of underwater surface it is called lava.
continental areas. volcanic eruptions.

Animals living in ocean trenches withstand pressures 100,000 The estimated number of 73
up to 800 times higher than the pressure at sea level. seamounts in Earth’s oceans.

Deep-sea smokers Smoke Mineral chimney
Often black but Can grow at an incredible
Usually found near can also be white. 12 in (30 cm) a day.
mid-ocean ridges, subsea
Tube worms
smokers grow where Conduit Unique ecosystems develop in
clusters around some smokers.
super hot water spurts up A passage that
MANY SUBSEA SMOKERS
from the seabed. Seawater hot water moves HAVE NAMES, INCLUDING

seeps down into the through. MAGIC MOUNTAIN,

seafloor and gets heated. LOKI’S CASTLE,

The hot water rises and FRED’S FORTRESS,

surges back into the cold GODZILLA,

ocean, where minerals Cold seawater HULK, AND

dissolved in it turn into This seeps HOMER SIMPSON.

solid particles, which look down through Hot rock, or magma
like smoke. The particles cracks in the This heats water that has
also build up to form solid oceanic crust. seeped into the crust.

chimneys around the

plumes of hot water.

Super-heated water

Can reach temperatures

above 750°F (400°C).

Seamount Volcanic island arc Under the sea
An underwater A slightly curved line
volcano that may of volcanic islands, found The seafloor lies about 2.3 miles
be active or extinct. where one plate slides under (3.7 km) below the surface of the
another at a subduction zone. ocean. It is made of a rocky oceanic
crust, which is covered in muddy
Abyssal plain Volcanic island sediment. Tectonic plates are generally
A flat expanse of The above-water made up of this oceanic crust and
mud that covers a continental crust, along with part of
vast area of seafloor. part of a huge the mantle layer under it. Erupting
undersea volcano. magma on the seafloor can create
volcanic islands and seamounts.

Sea level
The sea surface level,
which varies very
slightly over time.

Tectonic plate Oceanic crust Ocean trench Magma chamber Volcano
Each tectonic plate is This type of crust is thinner This forms where one A pool of magma Forms from a buildup
made of crust and the top than continental crust, and tectonic plate moves beneath a volcano. of lava when magma
layer of the mantle. made of dark-colored rock. under another. erupts at the surface.



NATURE

Since the first living organisms appeared on Earth
3.8 billion years ago, millions of different species have
evolved. Life now flourishes all over the planet, from
the highest mountain peaks to the depths of the ocean.

76

SIGNS OF LIFE HOW LIFE
BEGAN
Planet Earth was formed from a cloud of space rock, dust,
and gas. For millions of years it was a mass of hot molten Billions of years ago, a chance combination of chemicals
rock with a poisonous atmosphere. But eventually its crust somewhere on Earth’s surface created a substance
cooled to the point where water could form vast oceans. that could soak up energy and reproduce itself—the
The shallow fringes of these oceans were probably where first living organism. This was the beginning of
life began, about 3.8 billion years ago, in a series of the amazing story of life on Earth.
chemical reactions that assembled the first living cells.
VARIETY OF LIFE
1 EARLY EARTH
For 500 million years Earth As soon as life began, it started to change. Living things thrive by
was a giant furnace of searingly making copies of themselves, but the copies are not exact. Over
hot rock, constantly bombarded time, the differences generate new forms of life. This process of
by asteroids and meteorites. As change, called evolution, has created the diversity of life on Earth.
each lump of space rock crashed
into the planet, its energy was Evolution
converted into more heat. But
these impacts also delivered Every living thing is slightly different from its parents. If the difference
chemical elements that were helps it to survive, it is likely to pass on the advantage to its own young.
to be vital ingredients of life. This is the basis of evolution. Many years later, it may lead to a change
that is large enough for the result to be called a different species.
2 CHEMICAL CAULDRON
As the planet cooled, huge The ancestor A hooked bill is
volcanoes filled the air with toxic cracked seeds used for slicing
gases. But they also erupted vast with a thick bill. through fruit.
quantities of water vapor that
cooled and fell as rain, filling the A probing bill Overbite is
oceans. Lightning may have then pulls seeds perfect for
triggered chemical reactions in the digging grubs.
water, forming complex molecules from flowers.
that were able to make copies of
themselves—the basis of life. A pointed bill Galápagos finches
is used to These finches live on the Galápagos
3 FIRST CELLS Islands. Over time, they evolved bills
The chemical processes that peck insects. that differed from their big-billed
were essential to life needed to ancestor and allowed them to tackle
occur in a protected place. This A woodpecker finch the more varied food sources
was provided by a substance that uses a stick to dig available on the different islands.
could form tiny, tough-walled out prey.
bubbles. These were the first
living cells—microscopic packages Natural selection
of life-giving chemicals that
became bacteria, the simplest The main mechanism of evolution is called natural selection. Life in the
surviving life forms. natural world is a competition, with losers and winners. Those that survive
and breed happen to have a combination of qualities that helps them thrive
4 ENERGY FROM LIGHT in their habitat. But if conditions change, the winners may turn into losers.
Life needs energy. The first
cells used chemical energy, but Survival of the fittest The pale moth is
about 3.5 billion years ago cells Most peppered moths hard to see on the
called cyanobacteria started have pale wings for natural tree bark.
using solar energy. They used camouflage. But a dark
it to make food from water and form thrived in places The pale moth stands
carbon dioxide, releasing vital with smoke-blackened out on the soot-
oxygen. Similar cyanobacteria trees because it was stained tree bark.
created these stromatolites on less obvious to birds.
the coast of Western Australia.

5 DEEP HEAT
It is likely that the first living
cells developed in warm, coastal
pools of salty water. However,
life may have begun in the deep
ocean, around hot volcanic vents
that gush energy-rich chemicals
from the ocean floor. Simple
organisms that still live around
these vents are probably very
like the earliest living cells.

77

WRITTEN IN STONE Fossil hunters

We know that life has evolved The scientists who study fossils are
over time because rocks called palaeontologists. They are
contain evidence of different experts at finding, identifying, and
life forms that thrived in the preserving fossils. They can also
distant past. These links with work out how old each fossil is,
a vanished world are called and how it fits in with the story of
fossils. Typical fossils preserve evolution. They often have only
the forms of bones, teeth, and fragments to work with, but a
shells. By comparing them single bone can be a crucial clue.
with those of familiar animals,
scientists can piece together Excavation
the story of evolution. Every Palaeontologists painstakingly uncover
new fossil that is discovered a fossil of a 10-million-year-old
makes the picture clearer. rhinoceroslike animal in Nebraska.

The lightweight The knee and The size of the feet
foot was controlled ankle were flexed shows whether it was
by tendons instead a slow or fast runner.
like an ostrich.
of muscles.
must work out how they fitted together, On the move
Solving the puzzle what the living creature might have looked Study of the bones and joints of Tyrannosaurus rex has
like, and how it might have behaved. been used to create this computer simulation, showing
Fossils can be impressive, but even the biggest that its running action was similar to that of an ostrich.
and best preserved are just a start. To make
sense of a group of fossil bones, palaeontologists

CHANGING PLANET Snapshot of life When complex life appeared, the
pace of evolution accelerated to
The history of life is not a For about 84 percent of life’s create a dazzling variety of species.
story of steady progress. 3.8-billion-year history, the largest
Living things have faced many life forms were microscopic bacteria.
global disasters caused by
things like asteroid impacts EARTH FORMS TODAY
and climate change. Some have
left very few survivors, which In the beginning Complex life evolves
have had to live in an altered For 3 billion years, only the very simplest
world. This has changed the single-celled forms of life existed on Earth. Multi-celled life—the first animals—only
direction of evolution several
times, so new types of animals
and plants have evolved while
others have become extinct.

started evolving 600 million years ago (MYA).

Mass extinctions ORDOVICIAN (440 MYA) DEVONIAN (358 MYA) PERMIAN (250 MYA)
This extinction destroyed 60 percent of More than three-quarters of the species At the end of the Permian, life suffered a
Since life began there have the species living in the oceans. At the living in the Devonian Period were wiped out. global catastrophe that almost destroyed
been five mass extinctions— time, there was little if any life on land. Life in shallow seas was most badly affected. life altogether. Very few species survived.
catastrophic events that
killed off a large proportion 60% 75% 96%
of life on Earth. After each
extinction, life recovered TRIASSIC (200 MYA) CRETACEOUS (66 MYA) IN THE PAST 500 MILLION
slowly, and new types of The first period of the dinosaur era—the The mass extinction that destroyed the giant
animals, plants, and other Mesozoic—ended with an extinction that dinosaurs at the end of the Cretaceous was YEARS, MORE THAN
living things appeared. killed off most of the dinosaurs’ competitors. possibly caused by an asteroid impact.
These extinctions were 90 PERCENT OF
caused by natural forces, 70% 75%
but evidence suggests that ALL LIFE ON EARTH
we are in the early stage
of a sixth mass extinction, HAS VANISHED.
caused by human activity.

78 nature HOW LIFE BEGAN Animals have existed on Earth for more than 600 million years
and humans for about 200,000 years—a tiny fraction of the time.

PALEOGENE66–23 MYA
A new era, the Cenozoic, opened with the
Caudipteryx Paleogene Period—a time of slowly cooling
Many small predatory dinosaurs had climates when mammals evolved rapidly
feathers just like those of birds. to take the place of the extinct dinosaurs.

Uintatherium
The size of a modern rhinoceros,
Uintatherium was a plant-eating mammal.

Key Archaeanthus 145–66 MYA CRETACEOUS Allosaurus
Early Earth A small-sized plant, The Cretaceous Period About 25 ft (7.5 m) long
Palaeozoic Era Archaeanthus had saw the evolution of the and armed with knifelike
Mesozoic Era flowers like those of first flowering plants, and teeth, Allosaurus was
Cenozoic Era a modern magnolia. some of the most spectacular well equipped for hunting
dinosaurs. It ended with a mass the huge plant-eating
extinction that wiped out the dinosaurs of its time.

big dinosaurs, and ended
the Mesozoic Era.

Timeline of life Rolfosteus CARBONIFEROUS358–298 MYA
This long-snouted Life on land flourished
Life has existed on planet Earth for fish was a late Devonian during the Carboniferous,
3.8 billion years. Over that time, it has with dense forests of
evolved into a dazzling diversity of forms, shellfish-eater. tree-sized primitive
from microscopic bacteria to giant dinosaurs. plants. Insects and
spiders were common,
For most of Earth’s long history, the only living things and were hunted
were single-celled microbes that lived in the oceans. by large amphibians.
But around 600 million years ago, the first multicellular
animals appeared. This led to an evolutionary explosion Drepanaspis DEVONIAN
of complex oceanic life forms during the Cambrian Period. The head of this armored,
And once the first simple plants had evolved, life was able jawless fish was covered with a
to colonize the continents as well as the oceans. broad, flattened shield. It grew
to about 14 in (35 cm) long.
Geological time
419–358 MYA
The history of life is recorded by fossils The Devonian is known as
preserved in rock layers. Older rocks lie
beneath more recent ones, so each layer the age of fish because so
represents a span of time. Scientists divide many new types evolved.
this vast stretch of time into eras, and these Some of these fish gave rise
are further divided into smaller time spans to four-legged amphibians
called periods. This geological timescale that were the ancestors of
is the basis of the timeline shown here, all land vertebrates, such
measured in millions of years ago (MYA). as reptiles and mammals.

PRECAMBRIAN 4.6 billion to 541 MYA Early volcanoes
The huge stretch of time Water vapor erupting from
known as the Precambrian ancient volcanoes created the
Period includes the 3 billion oceans where life evolved.
years when only the simplest
single-celled life forms existed. Comets
The first animals evolved Space debris bombarded Earth in
near the very end of the early Precambrian, including icy
the Precambrian.
comets that melted into the oceans.

380 million years ago, the first vertebrate Insects were the first flying animals. Today, these thriving 79
animals crawled on to land. life forms make up more than 75 percent of all animal species.

NEOGENE 23–2 MYA QUATERNARY2 MYA to the present Homo neanderthalensis
The cooling climate
trend continued in the This period of dramatic These tough, strongly
Neogene. Modern types
of mammals and birds climate changes has had built people were
appeared, and the
australopithecine Australopithecus afarensis long ice ages with warmer adapted for life
ancestors of humans This early hominid could have phases like the one we live in icy climates.
evolved in Africa. been the first to walk upright,
4 million years ago. in today. Despite this,

modern humans—Homo

sapiens—slowly spread

all around the world.

201–145 MYAJURASSIC Morganucodon
The dinosaurs The small, insect-eating
flourished during Morganucodon was one
the Jurassic Period, of the first mammals.
rising to become the
dominant animals on Eudimorphodon Plateosaurus
One of the earliest pterosaurs, This long-necked
land. They included dinosaur could reach
gigantic plant-eaters and Eudimorphodon had wings of up to gather leaves
stretched skin, and probably flew well. high in the treetops.
powerful predators.

TRIASSIC 252–201 MYA
PERMIAN Life recovered slowly from the
Meganeura 298–252 MYA Permian extinction that ended
A dragonflylike The Permian saw the dominance of the Palaeozoic Era. But by the
insect, Meganeura had a reptiles and the ancestors of mammals, end of the Triassic Period,
29 in (75 cm) wingspan. but ended in a catastrophic extinction. the first of the dinosaurs
had evolved, along with the
Lepidodendron Dimetrodon earliest airborne pterosaurs
Growing to 100 ft (30 m) or The fossils of this and the first true mammals.
more, this Carboniferous tree sail-backed carnivore are
had bark with a scaly pattern. among the most common
fossils of this period.

Cooksonia 443–419 MYASILURIAN The Precambrian Period
Found in most parts of The Silurian Period makes up 88 percent
saw the appearance of the entire history of
the world, Cooksonia was
one of the oldest plants of the first bony fish Earth.
to have stems. with hinged, movable
Sacabambaspis
jaws. Meanwhile, life This armored animal had
had spread on to land very close-set eyes that faced
forward. It had no jawbones,
in the form of simple like all the earliest fish.
green plants.

ORDOVICIAN 485–443 MYA
CAMBRIAN Life flourished in the oceans
541–485 MYA Marrella during the Ordovician. Many
Fossils of complex animals About 1 in (2 cm) long, different types of fish evolved
became common in rocks of Marrella lived on the during this period along with
the Cambrian Period, at the seabed. It had jointed legs other animals such as trilobites.
start of the Palaeozoic Era. like a crab and spines But the Ordovician Period
Many of these creatures running along its body. ended with one of the biggest
had evolved with hard extinction events in history.
shells, which is why they
survived as fossils.

80 nature HOW LIFE BEGAN 80 percent, or more, of all known dinosaurs
have been discovered since 1990.
The dinosaurs DINOSAURS

For 165 million years, life on Earth was Ornithischians Saurischians
dominated by the most spectacular animals
that have ever existed—the dinosaurs. The word ornithischian The saurischian dinosaurs
means “bird-hipped.” It refers of the early Mesozoic Era
The Mesozoic Era was a high point in the history to the way that the pelvic had pelvic bones that
of life, because it was the age of dinosaurs. These bones of these dinosaurs resembled those of lizards,
fantastic creatures included the biggest, heaviest, resemble those of birds. so the word saurischian means
and most terrifying of all land animals. They evolved The ornithischians also had “lizard-hipped.” But many of
into an amazing variety of forms, ranging from huge, beaks supported by special the later forms evolved
armored leaf-eaters to nimble, feathered hunters, jawbones. But confusingly the birdlike pelvic bones, which
and gave rise to the birds that still flourish today. birds themselves are small the birds were to inherit.
theropod dinosaurs, part of Saurischians also had longer,
Family tree the saurischian group. more flexible necks than the
ornithischians.
All the dinosaurs of the Mesozoic Era except the very
earliest species belonged to two main groups known as the
ornithischians and saurischians. The ornithischians evolved
into three main types that were nearly all plant-eaters.
The saurischians were divided into the mainly meat-eating
theropods and the big, plant-eating sauropodomorphs.

Marginocephalians Theropods Sauropodomorphs
These consisted of ceratopsians, Spinosaurus was one of the The sauropodomorphs included the
like this Pentaceratops with its biggest theropods—the group that biggest dinosaurs—colossal animals such
huge horned neck frill, and included all the powerful hunters. as Brachiosaurus. They were all plant-eaters
pachycephalosaurs with very They all walked on their hind that supported their immense weight on four
strong, armored skulls. legs, and many had feathers. pillarlike legs resembling those of elephants.
They had very long necks, which were often
balanced by equally long tails.

Ornithopods Thyreophorans Treetop browser
One of the most successful groups The thyreophorans included the Its unusually high shoulders and
of dinosaurs, the ornithopods ranged heavily armored ankylosaurs long neck allowed Brachiosaurus
from lightweight animals that ran and stegosaurs such as this to feed high in the treetops, like
on two legs to heavyweights like spiny Kentrosaurus. a super-sized Jurassic giraffe.
this Muttaburrasaurus. They were
all plant-eaters. Large body
Its immense size allowed this
dinosaur to have a very big
digestive system to process its
diet of tough, fibrous leaves.

One fossil site in China has yielded The biggest sauropod dinosaurs could 800 species of dinosaurs have 81
more than 7,000 dinosaur bones. weigh as much as 13 elephants. been named by scientists.

Strong legs Dinosaur stance Crocodile stance Lizard stance
All dinosaurs stood tall on straight Modern crocodiles are close relatives Lizards usually sprawl with their legs
Unlike modern reptiles such legs, so their weight—which could of dinosaurs, but their legs do not outspread and their bellies close to
as crocodiles and lizards, be immense—was fully supported. support their bodies quite as well. the ground, which slows them down.
the dinosaurs stood with
their legs beneath their
bodies in much the same way
as mammals. We also know
that many of them were
warm-blooded, which allowed
them to be more active than
modern cold-blooded reptiles.

Reptile neighbors Mosasaurus Pterodactylus FOSSIL
At up to 50 ft (15 m) long, Mosasaurus Like all pterosaurs, Pterodactylus was
The dinosaurs were not the only was a powerful predator that lived at a warm-blooded, furry-bodied animal REMAINS
giant reptiles living during the the very end of the age of dinosaurs. that probably flew as well as a bird.
Mesozoic Era. They shared their TELL US THAT
world with marine reptiles such
as Mosasaurus, and pterosaurs THE BIGGEST
like Pterodactylus. These animals PTEROSAUR
were not dinosaurs, although the WAS THE SIZE
pterosaurs were close relatives. OF A SMALL
Most were hunters, and some PLANE, WITH
marine reptiles had massively AN AMAZING
strong jaws. The pterosaurs were 39 FT (12 M)
much more lightly built, with WINGSPAN.
small bodies and long, efficient
wings of stretched skin.

The Mesozoic Era became extinct at the end of the Triassic, allowing
dinosaurs to flourish during the Jurassic Period. The last
The age of dinosaurs began 230 million years ago, during period, the Cretaceous, saw the evolution of an amazing
the Triassic Period. This was the first of three periods that variety of dinosaurs, including the fearsome tyrannosaurs.
made up the Mesozoic Era. The earliest dinosaurs had to
compete with other types of reptiles, but many of these

The supercontinent LAURASIA Pangaea split into NORTH
of Pangaea was GONDWANA Laurasia in the ATLANTIC
fringed by a single, north, Gondwana
immense ocean. in the south. AFRICA
SOUTH
PANGAEA AMERICA The South Atlantic
ocean opened up
between Africa
and South America.

Triassic Earth Jurassic Earth SOUTH
From 252 to 201 million years ago, all the The supercontinent split in two near the ATLANTIC
continents were joined together in a huge beginning of the Jurassic Period. The deserts
supercontinent with a vast desert at its heart. shrank, and the growth of lush forests provided Cretaceous Earth
Most plants and animals lived near the fringes. food for huge plant-eating dinosaurs. The Jurassic Period gave way to the Cretaceous
145 million years ago. The continents became
more fragmented, allowing many different
types of dinosaurs to evolve in various lands.

Catastrophe SCIENTISTS STILL

The Mesozoic Era ended 66 million years ago with a mass DO NOT KNOW
extinction event that eliminated all dinosaurs except the WHAT REALLY
birds. It may have been caused by the impact of a giant
asteroid in what is now Mexico. At the same time, huge KILLED OFF THE
volcanoes were erupting in India, and the combination BIG DINOSAURS,
must have had catastrophic effects on the climate. OR HOW BIRDS,
CROCODILES, AND
Asteroid impact OTHER ANIMALS
The asteroid that hit Mexico 66 million years ago was at
least 6 miles (10 km) wide. The high-speed impact of such MANAGED TO
a huge rock would have filled the atmosphere with debris
and dust, blotting out the Sun for many years. SURVIVE.

82 nature HOW LIFE BEGAN 28 years—the age of a dinosaur known as Sue,
the biggest Tyrannosaurus to be exhibited so far.

Forward-facing eyes Air sacs
The eyes faced further forward Air passed right through the lungs
than those of most dinosaurs. This
gave Tyrannosaurus the binocular and into a network of air sacs
vision it needed to judge distances before it was pumped out again.
accurately and target its prey. This allowed the lungs to absorb

Lungs more oxygen with each breath.
The lungs were like those
Ribcage
of birds—super efficient Strong ribs protected
for gathering the oxygen the dinosaur’s heart,
lungs, and other vital
needed to power the organs from damage.
hunter’s huge muscles.

Lower jaw Air sac
The jaws were deep
and short, allowing Shoulder
the jaw muscles to blade
exert huge pressure.

Massive neck muscles
The weight of the head was
supported by very strong neck
muscles. These also helped

with tearing prey apart.

Bone-crushing teeth Small arms Gizzard
Tyrannosaur teeth were bigger and Each tiny arm Big mouthfuls of meat
stronger than those of any meat-eating had just two and shattered bone
dinosaur found so far. The biggest were at sharp-clawed passed into a muscular,
least 8 in (20 cm) long. They were more like fingers. tough-walled gizzard to
spears than teeth—sharp-pointed to pierce be ground to a pulp.
thick skin and muscle, yet deep-rooted and
very tough to give them the strength to bite
clean through the bones of their victims.

Tyrannosaurus rex Heart
The heart was probably at
The most powerful land predator that has ever existed was least ten times the size of a
a giant theropod dinosaur—a super-sized killer armed with human heart. It needed to be,
massive jaws and teeth that could bite through solid bone. to pump blood around its

The tyrannosaurs were the most deadly hunters of the entire colossal body.
165-million-year Mesozoic Era—the age of dinosaurs. The biggest
and most famous of them, Tyrannosaurus rex, evolved only near Birdlike feet
the end of the era, a few million years before the global Theropods walked on their toes,
catastrophe that wiped out all the giant dinosaurs. It was
specialized for killing—inflicting huge bites that crippled its prey like birds. Each foot had three
or caused it to die of shock. It would then rip its victim apart, strong, forward-pointing toes,
biting out great chunks of meat and swallowing them whole.
and a small toe at the back.

Tyrannosaurs weighed as much More than 30 fossil Tyrannosaurus 60 The number of teeth 83
as an adult male African elephant. specimens have been discovered. in a tyrannosaur’s jaws.

Intestine Fact file TYRANNOSAURUS
As a dedicated hunter,
Tyrannosaurus only ate meat. When ......................... 68–66 MYA (late Cretaceous) HAD THE MOST
This is easy to digest, so the Habitat ..................................................North America POWERFUL BITE
dinosaur almost certainly had Diet ................................................................. Carnivore
a relatively short intestine. Length.........................................Up to 40 ft (12.4 m) OF ANY LAND

Backbone ANIMAL THAT HAS
The vertebrae that made
up the flexible backbone EVER LIVED—
had tall spines linked to
AT LEAST
strong muscles, giving
excellent back strength. FOUR TIMES

THE STRENGTH

OF AN ALLIGATOR’S.

Tail muscle Long, heavy tail
Massive muscles flanking Extending well beyond the hips,
the bones of the tail provided the long tail balanced the dinosaur’s
strength as well as the weight heavy head as it charged into the
needed for balance. attack on its hind legs.

Hip bone 3 million years—the length of
Like most theropods, the time that Tyrannosaurus may
tyrannosaurs had massive have terrorized the Earth.
bones extending forward
from their hips that helped Powerful muscular legs
support their intestines. Like all the theropod dinosaurs,
Tyrannosaurus stood on just two
Shock tactics powerful hind legs. These were
very muscular at the top, but
Typical carnivorous dinosaurs had teeth like slim near the ankle for speed.
knife blades, ideal for slicing through skin and flesh.
But these bladelike teeth were very slender and Stout claws
likely to snap off if the dinosaur bit into something Each foot was equipped with
hard. Tyrannosaurus and its relatives were different. stout, strong claws to grip the
Their teeth were sturdy spikes that could punch through ground. It is possible that this
virtually anything. This allowed tyrannosaurs to charge animal could run very well,
straight into the attack on their powerful hind legs. Most despite its weight.
of the dinosaurs they preyed upon didn’t stand a chance.

84 nature HOW LIFE BEGAN The fossil record is not complete even
though many fossils have been discovered.

How fossils form Types of fossil Preserved in amber
This mosquito was trapped in
Fossils are a window on a lost world. They are our only Many fossils are shells sticky tree resin millions of years
evidence of spectacular creatures that lived long ago, or bones that have been ago, and preserved because the
and of the process of evolution that created them. turned to stone, but there resin hardened into a fossilized
are other types of fossils. form called amber.
A fossil is something that preserves the form or traces of Some are animals that
a living thing that died many millions of years ago. When were not turned to stone
something dies, its remains are usually broken up and attacked but simply preserved,
by decay organisms that completely destroy it. But some parts like flies in amber. Stony
are more likely to survive than others, especially the shells, fossils can preserve an
bones, and teeth of dead animals. If they escape destruction impression of something
for long enough and are buried below ground, they may be rather than its entire
replaced by minerals dissolved in groundwater. These can form, such as a footprint.
then harden to stone, creating a typical fossil. These types of trace fossil
can tell us a lot about how
long-extinct animals lived.

A long process Conifers Flooded landscape Megalodon
Fossils of needle-shaped The dinosaurs have A colossal relative of
Most of the time, fossilization is a leaves and bark show the great white shark,
gradual process. After thousands of that pines and other died out and the this was the biggest
years, a shell or bone can look as if cone-bearing trees were land is now covered killer in the oceans
it has been buried for just a few common during the 20 million years ago.
weeks, especially if it has been dinosaur age. by seawater.
frozen. Creating a stony fossil
usually takes millions of years Triceratops
as the body tissue of an animal This leaf-eater
is gradually replaced with the lived alongside
minerals that will eventually Tyrannosaurus,
turn it to stone. The result often and was among
mimics the original in every its main prey.
tiny detail, and this gives
scientists vital clues about
the animal and how it lived
in the distant past.

Tyrannosaurus rex
This famous dinosaur
was a bone-crushing
hunter that lived at the

end of the dinosaur
age, about 66 million

years ago.

Tyrannosaurus dies

Sediment layers
Different sediments
(mud or sand) form

layers that vary in
color and thickness.

Ammonites
These extinct relatives
of cuttlefish and squid

had strong coiled
shells that are very
common as fossils.

1 Deadly battle 2 Bare bones 3 Deep burial
Badly injured in a battle with a Lack of oxygen deep in the river Mud settling on the riverbed buries
rival, a Tyrannosaurus rex stumbles slows the decay process. Eventually, the skeleton. Then, millions of years
into a river and dies. Its huge body the body of the Tyrannosaurus is later, rising sea level floods the area with
settles on the riverbed, where its reduced to a bare skeleton, but the seawater, and the mud is covered
skin and flesh start to decay. bones stay intact as they were in life. with a pale layer of marine sediment.

The first known dinosaur fossils were identified 3,450 The age in millions of years In China, dinosaur fossils were once 85
in 1824—the teeth and bones of Megalosaurus. of the oldest known fossils. thought to be the bones of dragons.

From wood to stone Leaving an impression Natural cast Trace fossil
Plants are fossilized as well as animal Sometimes an organism, such as this Minerals dissolved in water can This three-toed footprint was left in
remains. Entire tree trunks can be slowly build up inside a mold, mud by a predatory dinosaur more
turned to stone (a process known marine animal Dickinsonia, sinks into re-creating the shape of the original than 66 million years ago. A line of
as petrification), which preserves soft mud that turns to rock, but then organism. This fossil ammonite such prints shows the animal’s
the cell structure of the timber. dissolves to leave an impression of was created by such a process. stride length and how it moved.
its shape called a mold.

Dolphins Buried in ice Roaming mammoth Well preserved
New life forms A mammoth Mammoths were Thousands of years
inhabit the oceans. common on the later, the deep-frozen
dies and is mammoth is amazingly
buried in the northern grasslands well preserved with
frozen ground. during the last ice age. hair, vital organs, and

even its last meal.

Erosion exposes Reconstruction
the mass of ice A well-preserved, fossilized
containing the skeleton can be put back
mammoth’s body. together to show what the
animal was like. Scientists can
also use computers to model
its muscles and other organs,
and work out how it moved.

Exposed fossil

Palaeontologist

4 Bone to mineral 5 Ice age 6 Surface erosion 7 Excavation
As the sediment layers get deeper, Closer to our own time, an ice age A river changing its course cuts Long after the end of the ice age,
dissolved minerals turn them into turns so much water to ice that sea away the pale chalk rock, exposing more erosion cuts into the dark shale
solid rocks such as chalk and shale. level falls. Mammoths roaming the the frozen body of the mammoth. and reveals the dinosaur fossil.
The minerals seep into the buried half-frozen tundra occasionally stumble But the skeleton of the Tyrannosaurus Scientists known as palaeontologists
bones, slowly turning them to stone. into swamps, die, and freeze solid. is still hidden deep below ground. begin a careful excavation.

86

THE LIVING LIFE ON EARTH
WORLD
There is life almost everywhere on Earth, but some regions
Life has evolved into an incredible variety of forms, have many more species than others. Such areas are known
with almost 1.8 million known species and many more as biodiversity hotspots. The warm tropics are the richest –
yet to be discovered. Scientists classify them in six especially tropical rainforests and tropical coral reefs. These
kingdoms. Each kingdom is divided into groups of habitats offer many ways in which organisms can survive,
related living things called phyla, classes, orders, encouraging the evolution of different types of life.
and families. These organisms have evolved different
ways of surviving in their particular habitats, but many Key
find it harder and harder to live in a changing world. Major
biodiversity
hotspots
North America
South America
Europe
Africa
Asia
Australasia

LIFE FORMS main stems—the six kingdoms of life. Three of the How many?
kingdoms are made up of organisms that are mostly
Every species of living thing is related to others that too small to see without a microscope, but the Compared to plants, fungi,
evolved from the same ancestors. They form groups others consist of the animals, plants, and fungi. and protists, the animal kingdom
of species that are related to other groups in the has the largest total number of
same way, like a giant family tree. This tree has six named species. Bacteria and
archaea numbers run into millions
and are impossible to estimate.

The six kingdoms FUNGI AND
PROTISTS
1ARCHAEA
The first life forms to evolve on Earth 4FUNGI PLANTS
were the microscopic organisms called Although they seem to grow like
archaea. They have a very simple structure— plants, fungi feed on other living or dead ANIMALS
just a single cell enclosing a tiny drop organisms. Some fungi are single-celled
of watery fluid containing the molecules microbes, but most fungi form spreading, Key
vital to life. Some archaea live in hostile multicelled root networks. These Animals: 1,367,555
places such as hot, acidic springs. produce mushrooms and molds like Plants: 321,212
those that grow on decaying fruit. Fungi and protists: 51,563
2BACTERIA
These are very like archaea, with 5PLANTS
the same structure. But their chemistry Green plants are multicelled living
is different, showing that they evolved things that use the energy of sunlight to
separately. Some bacteria cause disease, make food. In the process, they release
while others are essential to our survival. oxygen into the air, which is vital to
One type, cyanobacteria, produced animal life. They mostly live on land or in
nearly all the oxygen in the atmosphere. fresh water, and range from low-growing
mosses to magnificent trees.

3PROTISTS 6ANIMALS SCIENTISTS ESTIMATE THAT
Also known as algae and protozoans, Like plants, all animals are THERE COULD BE UP TO
these are mainly microscopic, single- multicelled organisms. But unlike them,
celled organisms. Unlike bacteria or they cannot make their own food, and 8.7 MILLION
archaea, each cell has a nucleus that must eat other organisms instead. Most do
contains the main life-giving molecules. so by moving around, using their senses UNDISCOVERED SPECIES
There are also other structures within the to find the food they need, and this has
cell that make food or turn it into energy. led to the evolution of intelligence. OF ANIMALS.

Classification of life Within each family there are usually groups of Classifying a tiger
closely related organisms, each called a genus. The scientific name of an organism is made up
Each of the six kingdoms of life is divided This normally contains several individual species. of its genus and species. The tiger is in the genus
into several phyla of similar organisms. These Panthera, so its scientific name is Panthera tigris.
are split into classes, orders, and families.

KINGDOM PHYLUM CLASS ORDER FAMILY GENUS SPECIES

Animals Chordates Mammals Carnivores Cats Big cats (Panthera) Tiger (tigris)
Organisms made of These are mostly Warm-blooded, hairy A group of hunting Specialized hunters The most powerful The biggest of the
many cells that eat vertebrates—animals vertebrates with mammals that have with no chewing cats, including the forest-living cats,
organic matter to with backbones of females that feed special meat-slicing teeth. Many have lion, which share recognized by its
obtain energy. bone or cartilage. milk to their young. back teeth. retractable claws. an ability to roar. striped coat.

87

ESSENTIALS FOR LIFE Living things also need raw materials to Food chain
build their tissues, and energy to fuel the
All living things share certain basic needs. processes that turn chemicals into living All living things need energy. Plants and some
They must have water, for without it the cells. They get these in many ways, often other organisms gather energy from sunlight and
chemistry of life is not possible. The fact that relying on other organisms to supply them. use it to make sugar. Animals eat the plants and turn
Earth has liquid water on its surface is the the sugar back into energy and body tissues. Other
main reason why life evolved on this planet. animals eat the plant-eaters, so the energy—along
with vital nutrients—passes down a food chain.
But eventually, the energy and nutrients are turned
into a form that can be recycled by plants.

Living requirements Energy Producer
Plants and many This plant produces food by
While all living things need the same essentials, many have microbes soak up turning raw chemicals into
more specific requirements. For example, plants and animals solar energy. They use sugary carbohydrates and
get their energy in very different ways—plants need sunlight, it to make energy-rich proteins. It uses these to
while animals need energy-rich food. But few forms of life food that supports build its stems, leaves,
can manage without most of these basic necessities. other forms of life. flowers, and seeds.

Living space DESERT SHRUB
A plant needs soil
Water Shelter to take root, and an Primary consumer GERBIL
All life is made of cells Many animals live in animal must be able A desert gerbil eats the
that contain water, so hostile places where to find enough food. seeds, and digests them.
this is vital. Desert life they need shelter from Even a microbe needs This turns the proteins and
is able to survive on the Sun or cold winds, its own living space. carbohydrates in the seeds
very little water, but and even plants may into substances that build
cannot do without it. need some protection. Oxygen tissues such as muscles.
Most living things use
Warmth Nutrients oxygen to turn food Secondary consumer
Few living things can Plants absorb water into energy. Luckily, If a fennec fox catches and
survive in very cold or containing dissolved it is constantly being eats the gerbil, it digests
very hot places. Most minerals, using them released into the the meat and turns it into
live in regions that are to build their tissues. atmosphere by plants. nutrients and energy that
always warm, or have Animals get nutrients build its own body tissues
warm summers. from their food. and fuel its activities.

Energy pyramid FENNEC FOX

Most natural habitats have many All the food eaten DECREASING ENERGY AVAILABLE Top predator HYENA
organisms that produce food, and by the rabbits The fox becomes a meal WORM
several levels of food consumers. supports one fox. for a prowling hyena,
This patch of wild grassland so the nutrients and energy
supports several rabbits, which are The rabbits that are stored in its body
primary consumers, fewer weasels support a are passed on to another
that prey on the rabbits, and only few weasels. link in the food chain.
one fox—the top predator. There are
fewer consumers at the upper Rabbits use food Detritivore
levels, because at each level some for activity as well When the hyena dies, its
energy is turned into activity and as growth. body is recycled by animals
heat instead of food for the next such as worms. They turn
link in the chain. This means that Plants make food its tissues into chemicals
it takes a lot of grass to support for the rabbits. that the desert shrub can
one fox, and explains why foxes use to make more food.
are much rarer than rabbits.

UNDER THREAT Plants Reptiles

In every kingdom of life there The destruction of habitats Recent research shows that
are species that are threatened such as tropical rainforests more than a fifth of the reptile
with extinction. There are many is threatening the amazing species living worldwide are
reasons for this, but most of diversity of plant life. under serious threat.
them are the result of human
activity. Some animals are Fish Birds
deliberately killed, including
rare species. Vast areas of wild Although fish are not as Hunting and loss of their
habitat have been destroyed, threatened as some animals, natural habitats have made the
denying wildlife its basic needs pollution and overfishing have future uncertain for at least
such as living space and food. made many species scarce. 12 percent of bird species.
But creating wildlife reserves
can help save many species. Amphibians Mammals

Hardest hit of all are the One in every five mammal
frogs, salamanders, and other species is threatened,
amphibians, with a third of all including giants such as
known species vanishing fast. rhinos and elephants.

88 nature THE LIVING WORLD 5,000 years—the estimated age of the oldest living
plant, an American bristlecone pine tree.

Plant life Vital water PLANT KINGDOM

From creeping mosses to majestic All plants need water. Nonvascular Vascular
trees, there are plants growing all Most plants soak it up from
around us. They create most of the the ground, then draw it Absorbent Water is
food that supports animal life on up through their stems leaves pumped up
land. They also produce most of the and use it to make sugar. through trunk
oxygen that is in the air we breathe. Water pressure inside a Rootlike
soft-stemmed plant holds fibers Tree
Plants are multicelled living things that it up, so if it runs out of Most plants absorb water
mostly grow on land or in fresh water. water, the plant wilts and Moss through their roots, which are
Nearly all plants use the energy of collapses. But many plants Mosses absorb water directly connected to the rest of the
sunlight to turn water and carbon dioxide have strong, woody stems into their leaves, so mosses plant by a network of veins
into oxygen and sugar—a process called that do not wilt, and live in wet places where they called the vascular system.
photosynthesis. They use the sugar to their strength allows the will not dry out. They cling to This allows trees to grow
make the complex materials that form biggest trees to spread rocks and trees with rootlike high above the damp ground.
their roots, stems, and leaves. The most their leaves high above fibers, forming cushions that
primitive types of plants can only grow ground level. soak up water like sponges.
close to the ground in damp places, but
others grow tall and broad, covering the Types of plants
land with green vegetation that provides There are two main groups of
living space and vital food for animals. plants. Nonvascular plants, such
as mosses, were the first plants
to evolve. Unlike vascular plants,
they do not have internal vein
systems that allow water and
sap to flow all around the plant.

Flowering plants Petals Bee
Brightly colored petals Lured by color, scent,
Primitive plants, such as mosses and ferns, do not have attract insects and birds. and the promise of sweet
flowers or seeds. These nonflowering plants are now far But the petals fade once nectar, a bee picks up
outnumbered by flowering plants, which evolved during the flower is fertilized. some of the pollen.
the dinosaur era around 200 million years ago. Flowers
produce pollen, which is carried to other flowers of the Stigma Style links
same species, fertilizing them so they form seeds. When pollen lands on stigma to
ovary
Wind pollination Pollen the stigma, the male
Some flowering plants such as The tiny pollen grains cells in the pollen grain Sepals
grasses and many trees produce a contain the male cells Tough green sepals
lot of pollen that blows away on the that fertilize the female fertilize the flower. protect the flower bud,
wind. Some of it may land on plants cells of nearby plants. splitting apart when
of the same species, and pollinate Anther is filled the flower opens up.
(fertilize) their flowers. These plants with pollen grains Ovary
have small, plain flowers. This contains egg cells,
or ovules, which turn
Anther into seeds when they are
fertilized by the pollen.
Filament

Stamen
Pollen is produced
by structures called
stamens, each made
up of an anther and
a stalklike filament.

Stigma

Filament

Plain flower Animal pollination
A grass flower has a Many plants have colorful, often
simple structure, and no fragrant flowers that contain sugary
bright color or scent. nectar. The nectar attracts hungry
animals, such as hummingbirds, bats,
or insects. As they drink the nectar,
the animals get dusted with pollen,
which they then carry directly to other
flowers as they search for more nectar.

Green plants have existed on Earth 379 ft (115.5 m)—the height of a California redwood 10 ft (3 m)—the height of the world’s 89
for at least 400 million years. tree, which makes it the tallest plant on Earth. biggest flower—the Sumatran titan arum.

How plants grow The leaves are Life cycle
the plant’s food
When the seed of a flowering plant is warm and Some plants live for many years, flowering every year.
moist enough, it sprouts and starts to grow into source. They are called perennials. Others, called annuals, live for
a seedling plant. A root pushes down into the soil one growing season and produce tough-skinned seeds that
to draw up water that fuels the growth of a stem. The cotyledons survive the hard times. Many of these short-lived plants
In many plants, the stem carries two leaves become a pair grow in places that have very cold winters or scorching
formed from the two halves of the seed. summers. Biennials live for two growing seasons, surviving
of leaves. the cold or dry season as energy-packed roots.
This seed is of a
type with two halves Stem Seed lies dormant
through winter
called cotyledons.

The seed cover Side roots
has a hard coat
to protect it from
fungi and bacteria.

Root hairs Plant dies, Seed grows
but seeds into plant
in spring
survive

1 Germination 2 Roots 3 Stem Plant produces
A seed has a tough skin The seed sprouts a A loop at the top of the flowers that
that protects it for many root that grows downward. shoot pushes up, pulling the make seeds
months or even years. But Fine hairs on the root two halves of the seed into
eventually, moisture makes absorb water and dissolved the light. They become the Annual
the seed swell and split open. minerals from the soil. plant’s first pair of leaves. A field poppy produces hundreds of seeds that lie in the
ground all winter. In spring, they grow into new plants
Evergreen or deciduous Extraordinary plants that flower and produce more seeds. Similar plants grow
in deserts, where their seeds survive years of drought.
Many tropical plants grow all Most plants get nearly all their essential
year round. But other plants nutrients from the soil, stay rooted in one Seed sprouts to
must cope with cold winters that place, and harness the energy of sunlight to form new plant
stop their growth and could kill make food. But a few plants have evolved
them. Some survive by being other ways of living in places where Plant dies, Plant stores
very tough, but others have ordinary plants might struggle to survive. but seeds sugary food
evolved ways of shutting down in root
until the warm weather returns. survive

Insect lands Hairs are
on the leaf disturbed,
triggering the
leaf to shut Plant grows Plant lies
flowers that dormant all
make seeds winter

Evergreen trees Trigger Root grows new
Many conifers, such as these firs, hairs foliage in spring
have tough, needle-shaped leaves
that can survive freezing. They Venus flytrap Biennial
stay green all winter, so they are This amazing plant traps insects and digests Some plants have a two-year life cycle. A carrot seed
always ready to soak up solar them. Nutrients from the insect allow the plant grows and produces leaves that make food. It stores the
energy and make food. to live in places where the soil is poor. When food in a thick, juicy root that survives the cold winter.
the plant finishes its meal a week later, the In spring, the root produces flowers that scatter seeds.
leaf opens up again to trap another insect.

Oak tree Oak seed (acorn)
may live for forms young tree

centuries Mature tree is
ready to flower
Tree loses its
leaves in winter Tree flowers and
produces seeds

Deciduous trees Ferocactus Thyme broomrape Perennial
Oaks and similar trees have thin, During floods, the This plant cannot make These plants survive for many years, but may lose
very efficient leaves that make cactus’s hooked spines its own food. It lives their leaves in cold or dry seasons. A mature oak
all the food that the tree needs in catch on floating by attaching its roots tree produces flowers and seeds during each growing
summer. In winter, the leaves fall debris that carries the to thyme plants and season, and the seeds grow into new young trees.
off and new ones grow in spring. plant to new places. stealing their sap.

90 nature THE LIVING WORLD

Green energy Leaf absorbs
sunlight
Animals must find food, but green plants
make their own using energy from sunlight
to turn carbon dioxide and water into sugar.
This process is called photosynthesis.

A plant’s leaves act like solar panels. They soak up
solar energy to fuel a chemical reaction that combines
carbon, hydrogen, and oxygen to form glucose—a type
of sugar. This reaction also releases oxygen into the
air. The plant uses the glucose to make cellulose (plant
fiber), and combines it with nutrients from the ground
to make proteins that are used for growth.

Cross section through a leaf

Inside a leaf are thousands of microscopic cells that
act as food factories. Each cell contains tiny structures
called chloroplasts that are filled with green chlorophyll—
a chemical that absorbs sunlight and turns it into the
chemical energy needed for photosynthesis. Other cells
form the skin of the leaf, while a network of transport
vessels supply the leaf with water and carry away
sugar in the form of sugary liquid sap.

Leaf vein Spongy cell
Veins deliver water The region between the
palisade cells and the lower
to sugar-making epidermis is filled with spongy
cells and carry tissue. Air spaces between the
sugar away. cells allow gases to circulate.

Stoma
The leaf has tiny pores

called stomata. These
draw in carbon dioxide
and allow water vapor
and oxygen to escape.

Oxygen, the waste
product of photosynthesis,

escapes into the air.

Carbon dioxide from Guard cell
the air enters the leaf. Each stoma is made of two
guard cells. These cells swell
to open the stoma when the
Sun is shining, and shrink to

close the stoma at night.

The word photosynthesis means There are up to 500,000 chloroplasts All the food that supports life in the oceans is 91
“putting together through light.” in every square millimeter of leaf. made by tiny drifting algae using photosynthesis.

Protective cuticle Plants only look Water pathway
A coating of transparent wax
forms a waterproof layer on green because of the green In daylight, the stomata in a plant’s leaves
the upper side of the leaf. open up and allow water vapor to escape.
chlorophyll in their cells. The water vapor is replaced by water drawn
up though the xylem vessels from the plant
Upper epidermis stem and roots. This draws more water up
A thin layer of cells forms the from the soil, along with the dissolved
upper skin. The cells produce minerals that the plant needs to build its
the waxy cuticle that controls tissues. This process is called transpiration.
water loss by evaporation.
Water evaporates
Palisade cell through the
These tall, cylindrical cells stomata.
are the main food producers
of the leaf. Each palisade cell Tiny root hairs Water is
is packed with chloroplasts absorb water transported by
that absorb solar energy from the soil. the xylem vessels.
and use it to make sugar.

Chloroplast
Small green structures called
chloroplasts turn sunlight into
chemical energy and use this to
split water into hydrogen and
oxygen. Then they combine the
hydrogen with carbon dioxide
to form glucose—the plant’s food.

Vein
The veins transport liquids to
all parts of the plant. Each vein is
a bundle of tubular fibers made
up of chains of long, hollow cells
with walls of tough cellulose.

Oxygen factory

Photosynthesis by plants creates most of the
food on Earth and nearly all the oxygen that
we breathe. In a single year, one mature tree
releases enough oxygen to support ten people.

Lower epidermis
The skin and waxy
cuticle of the underside
is thinner because it
does not face the Sun.

Xylem vessel NEARLY 40 PERCENT
Some of the tubes within veins
draw water up from the roots of OF THE WORLD’S
the plant. This root sap contains the
dissolved minerals that the plant OXYGEN
needs to make proteins.
IS PRODUCED IN
Phloem vessel
Sugar made in the leaves is THE TROPICAL
dissolved in water and carried RAINFORESTS.
to other parts of the plant
through the phloem vessels.

92

AMAZING VARIETY INVERTEBRATES

Invertebrates come in every imaginable shape and size, Most of the animals that live around us on land and
from microscopic worms to giant squid. Some are familiar, in the oceans are invertebrates—animals that do not
like the insects that buzz around our homes, while others have backbones and jointed internal skeletons like
can seem like creatures from another planet. ours. Many have tough external skeletons, while
others have hard shells. But many more have soft,
Outnumbered 3% Vertebrates muscular bodies with no hard skeletal parts at all.
97% Invertebrates
Most of the biggest, most visible ARTHROPODS
animals on Earth are vertebrates,
including humans. But the total The biggest invertebrate group consists of the arthropods. They
number of vertebrate species include the insects, spiders and scorpions, and crustaceans. Adult
is suprisingly tiny compared arthropods have tough, jointed external skeletons or exoskeletons,
to the amazing diversity of several pairs of jointed legs, and—in the case of insects—wings.
invertebrate species.

Invertebrate groups Success story 20% All
other
The animal kingdom is divided into 35 major groups, each Arthropods account for more than
called a phylum, and each phylum is divided into classes. 80 percent of all known animal Animals
The vertebrates make up part of just one phylum. Here species. They are the most successful
are a few of the many phyla and classes of invertebrates. animals on Earth, conquering land, 80% Arthropods
sea, and air. Scientists discover about
SPONGES CNIDARIANS 25 new arthropod species every day,
10,000 species 11,000 species and there are countless more waiting
They may look like Sea anemones, jellyfish, to be discovered.
plants but sponges and corals like this one
are the simplest are all aquatic animals Front pair of legs Inside out
animals of all—they armed with stinging are armed with
don’t even have a tentacles, which they strong pincers The tough exoskeleton of an adult
nervous system. use to catch prey. arthropod is made of chitin, which
Each rigid is similar to the substance that forms
ANNELID WORMS CTENOPHORES segment has your fingernails. In some marine
20,000 species 200 species flexible joints crustaceans such as this lobster,
This earthworm belongs The comb jellies and the chitin is reinforced with chalky
to one of several groups their relatives are minerals. Its exoskeleton is a series
of soft-bodied animals very simple animals of rigid segments that enclose the
that we call worms. that drift with the animal’s soft tissues. These are linked
ocean currents. by thinner, flexible sections, forming
joints that allow the animal’s body
MOLLUSKS INSECTS and legs to move.
110,000 species 1.1 million species
The clams, snails, and This huge arthropod Heavy shell
cephalopods (octopuses group outnumbers Weighed down by its armored exoskeleton,
and relatives) form the all the other animal a lobster lurks on the seafloor, using its
second-largest group. species put together. powerful pincers to grab prey.

CRUSTACEANS ECHINODERMS Tight fit NYMPH Adult
70,000 species 7,000 species emerges
Crabs and other Meaning “spiny skin,” A hard exoskeleton cannot stretch, EGG
armored sea creatures echinoderms include so as an arthropod grows it has to FINAL
with jointed legs are starfish, sea urchins, shed its old, tight exoskeleton and ADULT STAGE
the most familiar and sea cucumbers. develop a bigger one. When it does CICADA
crustaceans. this, it emerges with a soft skin Old exoskeleton
that inflates to a larger size before is discarded
ARACHNIDS it hardens. The complex life cycles
103,000 species of many arthropods mean that
Venomous scorpions, spiders, they often change shape as well
and their relatives form a class as size when they molt.
of land-living arthropods.
Cicada life cycle
Like many insects, a cicada hatches from
its egg as a wingless larva, or nymph,
that eventually becomes a winged adult.

93

TAKING ROOT Snares and stings Stinging MOST INVERTEBRATE
tentacles ANIMALS ARE TINY,
Although many invertebrates Some marine invertebrates,
live on land, the most diverse such as sponges, mussels, Prey BUT THE GIANT
types live underwater. This and many clams, pump water Mouth
has allowed some to evolve a through their bodies and SQUID CAN GROW TO
completely different way of strain it for edible particles. Stomach
life, because instead of having Others spread nets in the cavity AN AMAZING
to go in search of food, they water to snare small animals.
can wait for food to drift their Sea anemones and corals 59 FT (18 M) LONG,
way, carried by the water. have crowns of tentacles
They don’t need legs or fins, armed with venomous INCLUDING ITS
and many never move at all. stinging cells that can even
These invertebrates spend stun and kill small fish. TENTACLES—THAT’S
their entire adult lives rooted
to one spot, more like plants Deadly crown Foot AS LONG AS
than typical animals. The cylindrical body of this sea sucker
anemone is crowned with a lethal THREE
cluster of stinging tentacles.
ELEPHANTS.

WONDERFUL FORMS LIVING TOGETHER

Many invertebrates such as insects have the familiar form of Many marine invertebrates that spend their lives rooted to one
a head equipped with a brain and two eyes, attached to a body spot live together in large groups known as colonies. Often these
that has an equal number of legs and even wings on each side. are individual animals that settle in the same place because it is an
But other invertebrates have a very different body plan. ideal habitat. But other colonial invertebrates are linked to each
other, like the twigs of a tree. They share the same body fluid
Stars and suckers middle of its body. An octopus circulation, but each has its own mouth and digestive system.
or a squid has a strange body plan,
An adult echinoderm such as a with muscular, sucker-covered Mussel colony
starfish has radial symmetry— tentacles that sprout from its
its body parts are arranged like head and surround its mouth. These mussels have all settled
the spokes of a wheel. It has no on this rocky tidal shore because
head, and its mouth is in the there is so much food for them to
eat when they are submerged at
Fully armed high tide. They are not linked to
Found throughout the world’s each other—they just need the
oceans, octopuses are intelligent same conditions to survive.
animals. They use their strong,
suckered tentacles to grasp prey.

Underwater garden
Reef corals grow in warm, clear sunlit
water on shallow tropical shores, just
below the low tide line.

Tentacles Reef corals
Suckers
Each head of coral on this reef is a
Holding tight colony of interlinked animals called
Attached to the rocks by strong coral polyps. They are like tiny sea
threads, mussels close their shells anemones that feed for themselves,
at low tide to avoid drying out. but together they form the distinctive
structure of a particular coral species.

Protective shells As the animals grow, they add extra Drifting colonies
layers of minerals to their shells, so
The soft bodies of many mollusks the shells grow too. They are often Some colonial invertebrates
are protected by shells made from lined with a beautiful, iridescent look like individual animals,
chalky minerals. Snails and similar layer called mother-of-pearl. such as the amazing Portuguese
animals have one shell, while man-of-war. It looks like a jellyfish,
bivalves such as clams have two. but it is actually a collection of
interconnected animals, each with
its own function. One is the float,
while others gather food, defend
the colony, or produce young.

CONCH COWRIE SCALLOP Stinging tentacles
The Portuguese man-of-war drifts on the
ocean surface, trailing long venomous
tentacles to ensnare its prey.

94 nature INVERTEBRATES The biggest insect that ever lived was Meganeura—an
ancient dragonfly with a wingspan of about 29 in (75 cm).
Insects
Compound vision
Both in terms of species and sheer numbers, insects The eyes of adult insects
outnumber all other animals on Earth. They are are made up of thousands
the most plentiful creatures on the planet. of tiny lenses, each with
its own set of light sensors.
More than a million different species of insects have been Every lens sees a dot of
scientifically named and described, and thousands more are color, and the dots add up
discovered every year. Thanks to their amazing adaptations, they to form a mosaic image.
flourish in every land habitat and play a key role in the global The more lenses, the
more detail the insects
ecosystem, recycling dead plants and animals, see. This system is very
pollinating flowering plants, and providing sensitive to movement.
food for a host of bigger animals. In fact,
insects are so vital to life on Earth Sensitive bristles
that we could not survive Many fine, touch-sensitive
without them. bristles on the insect’s body
help to detect air movement.

Antennae
The long antennae are covered

in nerve endings that detect
chemical signals. Some insects
can pick up scents from more

than 1 mile (1.6 km) away.

Head
An insect’s head is a strong
capsule containing its brain
and carrying most of its sense
organs. It swivels on a very

mobile neck joint.

Insect anatomy

Insects are the most numerous of the
arthropods—animals with tough external
skeletons and jointed legs. The bodies of all
adult insects are divided into three sections—
the head, thorax, and segmented abdomen.
All adult insects have six legs, and most
have one or two pairs of wings. But their
young, or larvae, are much more variable.

Jaws Claws Thorax Waist
This wasp has biting jaws, or mandibles, Each foot has sharp The central section of an Wasps need to
that pinch together. They have hard, sharp claws for clinging to insect’s body is called the curl their tails
edges that allow the wasp to cut and mash surfaces and holding thorax. It carries the legs forward to use
up its prey. Many insects have similar onto prey. Some insects their stingers, so
jaws, but the mouthparts of others are such as blow flies also and wings, and in most they have narrow,
highly modified for soaking up liquids, have sticky foot pads. insects it is packed with flexible waists.
sipping nectar, and even sucking blood. powerful wing muscles.

.

Legs
Each insect leg is made up of
a series of stiff tubes, hinged
together with flexible joints and
operated by internal muscles.

The first winged insects appeared A big dragonfly may have up to 1,046 The number of beats a second 95
more than 350 million years ago. 30,000 tiny lenses in each eye. a midge flaps its wings.

Wings Features
Most adult insects have wings. These
are flat plates of chitin—the tough Adult insects are
material that encases the body. very variable in
They are powered by muscles shape and size,
inside the thorax. but nearly all of
them share a few
key features. MOST HAVE WINGS COMPOUND
EYES

EXOSKELETON THREE BODY SIX JOINTED
SEGMENTS LEGS

Looking at insects Dragonflies and damselflies
5,600 species
Insects have been Large eyes and wings,
classified into about and slender bodies.
29 orders, and within
each order the insects
share the same features.
Shown below are some
of the major orders.

Veins Beetles Butterflies and moths
A network of fine tubes 370,000 species 165,000 species
called veins stiffens the Toughened front wings Nectar-feeding mouthparts,
wings so they can flex and that help protect the and overlapping scales on
twist in flight without hind wings. their bodies and wings.
collapsing under the strain.

Warning pattern
Vivid, contrasting stripes of
black and yellow warn birds
that this wasp has a stinger
in its tail, and help the wasp
stay out of trouble.

True bugs Flies
88,000 species 150,000 species
Two pairs of wings and Single pair of functional
long mouthparts that wings, with small balancing
pierce and suck. organs called halteres.

Abdomen Crickets and grasshoppers Ants, bees, and wasps
The segmented, flexible 25,000 species 198,000 species
abdomen contains most of Powerful hind legs and Have narrow waists and
an insect’s vital organs, chewing mouthparts. many live in colonies.
such as its stomach.

73 The percentage of all Painful sting FOR EVERY HUMAN BEING
known animal species Most insects are harmless, ON THE PLANET THERE ARE
that are insects—and but this wasp has a stinger
almost half of them are beetles. that it uses to kill prey or 200 MILLION INSECTS.
defend itself and its nest.

96 In Mexico, millions of monarch butterflies
spend the winter in the same trees each year.
The caterpillar
spins a silk pad, The old skin is
glues it to a twig, bunched up, hiding
and clings on with
the tiny claws of the silk pad.

its hind legs. The butterfly is now
fully formed inside its
transparent chrysalis.

The green chrysalis The butterfly’s head
is well camouflaged is visible at the lower

amid the leaves. end of the chrysalis.

3 Firm grip 4 New skin 5 Chrysalis 6 Metamorphosis 7 Taking shape
After about 14 A few hours Eventually, the Once the chrysalis is After nine or ten
days, the fully grown after attaching new chrysalis pushes its free of its old skin it gets days, the chrysalis
caterpillar crawls up a itself to its twig, the old skin right up to the shorter, smoother, and darkens as the skin of
twig and attaches itself caterpillar sheds its top. After reattaching its color changes to a the butterfly’s body
by its stumpy back skin again—but this itself to its silk pad with duller green. Inside, its turns black. The vivid
legs, hanging from time the striped skin is a thin black stem, it body is being completely black and orange
a pad of strong silk. pushed off to reveal a wriggles until the old rebuilt to become an pattern of the wings
bright green chrysalis. skin falls away. adult butterfly. also becomes visible.

The butterfly attaches
an egg on the shady
underside of a leaf.

2 Growing caterpillar Milkweed plant
The caterpillar spends Like many butterflies, the
its days eating, growing bigger monarch lays its eggs on just
all the time, and shedding its one type of plant—milkweed.
skin five times. Toxins in Its caterpillar eats this until
the milkweed leaf become it is ready to become an adult.
concentrated in its body
as it eats, making it
poisonous to birds.

Wasplike stripes
warn birds that the

toxic caterpillar is
dangerous to eat.

From egg The strong jaws chew
to butterfly through the leaf.

The metamorphosis 1 Larva
from newly laid egg to The female butterfly
adult monarch butterfly lays her tiny pale green
takes about a month. The egg eggs on milkweed plants.
hatches as a tiny caterpillar Each egg is the size of a
that eats voraciously for two pinhead, with a beautifully
weeks, bulking up its body until sculpted shell. Several days
it is big enough for the pupa later, the egg develops into
stage—the ten days that see a baby caterpillar that
it turned into a butterfly. chews its way out, then
eats the shell before it
starts feeding on the leaf.

20,000 The number of butterfly 3,000 miles (4,800 km)—the distance 50 million—the number of years that 97
species that live worldwide. that some monarchs migrate. butterflies have existed on Earth.

30 The number of days An extraordinary journey
that a typical monarch
butterfly lives as an Monarch butterflies spend the winter asleep
adult. But the ones that migrate in the warm woods of Mexico and California.
south may live for eight months. In spring, they wake up and fly north to find
milkweed plants, which do not grow in the
warm southwest. They lay their eggs and die.
The next generation flies further north and
does the same. After two more generations
they reach the Canadian border. Then the
fourth generation migrates all the way back
south again—clear across the US.

The empty CANADA
chrysalis is left
hanging after Roc Northern limit of
the butterfly milkweed plants Great
has flown. ky Mountains

Lakes

USA

California

The new wings are MEXICO
soft and crumpled,
but do not stay
like this for long.

Key Winter range
Northerly migration
Summer range
Spring range

8 Chrysalis splits 9 Wings expand Antennae
Soon after the body turns The butterfly pumps The long antennae are
black, the chrysalis splits near fluid from its body into the mainly for detecting scents
the bottom and the butterfly hollow veins of its wings, such as the fragrance of
starts to push its way out. and this makes them expand
At first, the butterfly’s body is to their full size. This process nectar-rich flowers.
very fat while its wings seem takes about 20 minutes. Then
much too small, but it soon the butterfly must wait for Eyes
starts changing shape. its wings to dry and harden. Like other adult insects,
a butterfly has compound
eyes made up of many
microscopic lenses.

Warning colors Scale-covered wings
The adult still contains the Tiny scales cover the
poisons that it picked up as wings like roof tiles.
a caterpillar, and its bright These give the wings
their color.
colors warn birds of this.
10 Adult butterfly
Butterfly lifecycle Within two hours of emerging,
the butterfly is ready for its first flight.
The beautiful monarch butterfly starts life as a It flexes its wings a few times before
wingless caterpillar that spends most of its time launching itself into the air. It will find
eating. Its metamorphosis into a butterfly is one some sweet nectar to drink, then start
of the most dramatic changes in nature. looking for a mate so it can breed and
create a new generation of caterpillars.
Some insects hatch from their eggs as miniatures of their
parents. As they grow they have to keep shedding their hard
external skeletons, which is difficult and dangerous. But many
insects, such as butterflies, moths, beetles, and flies, have
evolved a better solution. They do all their growing during
a stage of life called a larva—a sausage-shaped creature
that can shed its skin easily. When the larva is fully grown,
it enters a phase called a pupa, or chrysalis in butterflies.
During this stage it is transformed into a winged adult.

98

VERTEBRATES THREE PERCENT Vertebrate groups

Most of the more obvious animals that live around us Scientists classify animal We generally think of the vertebrates
are vertebrates—animals with flexible backbones and life in 31 major groups, each as divided into five main types of
internal skeletons. They are the mammals (which called a phylum. Just one of animals—mammals, birds, reptiles,
include humans), birds, reptiles, amphibians, and three these phyla—the Chordata— amphibians, and fish. But the fish
types of fish. Compared to the immense diversity of contains all the vertebrates, actually consist of three very different
animal life in general, there are relatively few species which add up to only groups of animals that happen to live
of vertebrates, but they include the biggest animals 3 percent of all the animal underwater, breathe with gills, and
now living on land and in the oceans, as well as the species known to science. have similar body forms with fins
largest that have ever lived—the giant dinosaurs. However, most of the other rather than legs. So scientists classify
97 percent of species, the the vertebrates into seven main groups.
invertebrates, are very small These make up the vast majority of
by comparison, so they can the phylum Chordata—animals with
survive in far less living a spinal nerve cord reinforced by a
space than is needed by tough, flexible rod called a notochord.
a typical vertebrate. In most vertebrates, the notochord is
replaced by a bony spine at a very
early stage in the animal’s life.

BODY PLAN Tetrapods Eusthenopteron Tiktaalik Acanthostega
This lobe-finned Stronger fins allowed This was probably the
Apart from a few primitive Modern lungfish and fish had muscular, Tiktaalik to climb out first vertebrate animal
jawless fish, all vertebrates coelacanths belong to limblike fins. of the water. to have feet and toes.
have flexible spines made of an ancient group of fish
chains of small bones called equipped with four fleshy WATER ON TO LAND LAND
vertebrae. They also have fins supported by strong
strong skulls. Fish have other bones. About 380 million LOBE FIN LEGLIKE LEG WITH
skeletal elements that support years ago, some of these FIN FOOT
their gills and stiffen their fins. lobe-finned fish were
All other vertebrates—even living in freshwater
snakes and whales—have swamps, where they
evolved from ancestors that started using their fins
were the first four-legged land as legs. Eventually, they
vertebrates, or tetrapods. crawled right out of the
water to become the
earliest amphibians.

SUPER-SIZED ANIMALS In the lineup
Apart from whales, the largest living vertebrates include
All the biggest animals that have ever lived are, or were, the sharks, elephants, hippos, giraffes, bears, and big cats.
vertebrates. This is largely because the strong internal But these animals would have been dwarfed by some
skeleton allows a very heavy creature to support its own of the dinosaurs that lived in the distant past.
weight. Some extinct dinosaurs such as Argentinosaurus
were probably as heavy as is possible for a land animal. The whale shark lives
The only known vertebrate that weighs more is the blue in tropical oceans.
whale, which relies on the water for support.

A blue whale can be
98 ft (30 m) long.

DIPLODOCUS BLUE WHALE WHALE SHARK GIRAFFE
One of the largest dinosaurs, this This is probably the heaviest animal This is the biggest fish in the Its incredibly long neck gives
115 ft (35 m) giant was a plant eater. that has ever existed—weighing sea, growing to 39 ft (12 m) long. the giraffe a total height of up
It lived during the Jurassic Period, anything up to 170 tons. Its heart Although a shark, it feeds on tiny to 20 ft (6 m). It towers above all
about 150 million years ago. alone is the size of a small car. shrimplike creatures and small fish. other animals—even elephants.