Exercise
1. Define an environment.
2. What is environmental pollution?
3. What are the major pollutions found in Nepal?
4. What is air pollution?
5. List any 3 effects of polluted air.
6. How can you suggest to reduce air pollution? Give 3 ways.
7. Define water pollution. Write its adverse effect in human health.
8. Mention any 3 ways to reduce water pollution.
9. What is land pollution? Write any 3 effects of land pollution.
10. Write in short.
a) Watersheds b) Water Management c) Forest management
11. How can we conserve water resources? Write any 3 points.
12. How can we do management of forest? Mention any 3 methods.
13. Choose the correct alternatives from the following options.
i. The full form of BHC is:
a. Bromine Hydrogen Chloride b. Benzene Hydrogen Chloride
c. Benzene Hexa Chloride d. None of the above
ii. Which type of pollution is caused by chemical fertilizer?
a. Land b. Water
c. Air d. All of them
iii. The major effects of air pollution is:
a. Decrease in amount of oxygen b. Air borne disease
c. Acid rain d. All of the above
iv. The region which is always wet with water is called:
a. Pond b. Wet land
c. Water shed d. Both ‘b’ and ‘c’
v. The best way to minimize every type of pollution is:
a. Public awareness b. Afforestation
c. Self-discipline d. All of the above
Blooming Science Book 10 301
Chapter History of the Earth
21
Lesson Objectives Estimated Periods: 4+1
On the completion of this unit, the students will be able to:
explain the history of earth from study of fossils.
identify the theories in support of origin of earth.
describe the evolution of life in different geological eras.
differentiate between fossilization and fossil fuels.
write importance of fossil fuels and mineral oil.
Introduction
Being a member of solar system and revolves round the sun, the origin of earth must be related
to the origin of the solar system. Earth science is the study of nature, distribution, behaviour and
origin of the materials of the earth and its atmosphere. Earth science combines the sciences of
geography, geology, geochemistry, geophysics, meteorology and paleontology under a single
course of study. It involves the application of principles from astronomy, biology, chemistry and
physics.
The study of the Earth Science includes mostly things of the Earth. Therefore, study of Earth
Science is known as Geology. The scientists related to earth science are called Geologists.
Origin of the Earth
On one side, philosophers’ thoughts and saying are taken as base for the support of the creation
of the earth while on the other hand, geological proofs given by geologists on what the Earth
came across are taken as bases about the creation of the Earth. The most important resources of
the geologists are the rocks. From the analysis of facts obtained from the deep study of rocks and
fossils, they have started to claim that they could tell situations of the Earth before 450 million
years. However, the proofs of writers or archaeological evidences are available only of the last
6 thousand years.
Science is a subject that makes efforts to get as much information as possible about the estimated
time, 600 million years of Earth’s creation, how many and how big incidents occurred, how many
changes took place and how many earthquakes did the Earth feel? Human beings can know about
60-70 years’ old incidents that happen during their lifetime. Had there been no evidences, there was
no way to know about Earth’s situation of millions of years before. How interesting would it be to
know all the facts that had happened before? We feel amazed when geologists tell us that:
(a) When rock from the top of the Mt. Everest is tested, it is proved that the rock was under
ocean water a long time ago.
302 Blooming Science Book 10
(b) Scientists have found some rhinos, elephants, hippopotamus, tigers, etc. that are not available
in the jungles of United Kingdom now a days, used to live in the same jungle long ago.
Numerical Expression
United State Great Britain
1,000,000 = 1 million 1,000,000 = 1 million
1,000,000,000 = 1 billion 1,000,000,000 = 1 thousand million
1,000,000,000,000 = 1 trillion 1,000,000,000,000 = 1 thousand billion
Note: We have followed US method in numerical expression.
Facts related to Earth
Approximate age: 4.5 billion years
Surface area: 509,700,000 sq. km
Land area: 148,400,000 sq. km
Hydrosphere: 361,300,000 sq. km
Diameter: 12,756.3 km
Relative density: 5.5
Mass: 6×1021 metric ton
No. of satellite: 1 (moon)
Major gases: N2, O2, CO2
Some Hypothesis about Origin of the Earth
We should know about the origin of the solar system that tells us about the origin of the Earth
because of Earth is a member of the solar system. Despite human researches, the information
about the space outside the Earth is insufficient. So, many different theories about the Earth’s
creation or origin of the solar system are presented. The hypothesis are presented below in
chronological order of their formation.
1. Planetesimal Hypothesis (Georgr Wotan Hypothesis)
A french philosopher named George wotan put forth old planetesimal hypothesis in 1749
AD. This hypothesis states that a huge gaseous mass and a comet collided together; as a
result a very large amount of matter was thrown out of the sun. These hot matters cooled
and the Earth with other planets was formed. The remaining mass was the sun.
2. Nebular Hypothesis (Kant Hypothesis)
Immanuel Kant, a German philosopher proposed a nebular hypotheses for the origin of the solar
system in 1755 A.D. A French astronomer, Pierre Simon Laplace refined Kant’s theory in 1796
A.D. Laplace suggested that the original nebula was much larger than the present solar system
and left behind eddies of matter as it became smaller. This theory assumes that the earth was first
Blooming Science Book 10 303
a gas and then a liquid and finally cooled enough
to have a solid crust.
According to this hypothesis, the solar system
developed from a huge nebula (cloud of gas and
dust) that once swirled around the sun. The sun
itself may have been formed from the central part
of this nebula. As the nebula whirled around the
sun, it slowly flattened out. Sections of the cloud
began to spin like eddies (whirlpools) in a stream. Nebular theory
Gas and dust collected near the centers of these eddies. The collections of gas and dust grew by
attracting nearby particles of matter. They slowly developed into the spinning planets that now
travel around the sun.
Some gas and dust particles, which were closed to planets
joined the planets but some of those which didn’t join formed
satellites or moons and meteors. These phenomena, in fact,
should have happened in cold rather than in a hot situation.
Therefore, according to this theory, the earth was cold from the
very beginning.
3. Tidal or Gaseous Hypothesis (Jean and Jeffery Hypothesis)
Two English Scientists, Sir James Jeans and Harold Jeffer, proposed the tidal or gaseous theory
in 1917 A.D. Like the planetesimal theory, the tidal theory begins with arms of hot gas pulled
from the sun by the gravity of a passing star. The gas gathers in eddies which turn into liquid
balls. Each liquid ball slowly cools and a hard crust forms around it. This theory assumes that the
earth was first a gas and then a liquid before it developed a solid crust.
The Earth’s Early Development
Scientists do not know any more about the earth’s earliest stages than they do about the birth of
the solar system. They supposed that the Earth began as a Waterless mass of rock surrounded by
a cloud of gas. Radioactive materials in the rock and increasing pressure in the earth’s interior
gradually produced heat to melt the interior of the Earth. The heavy materials such as iron,
then sank. The light silicates (rocks made of silicon and oxygen) rose to the Earth’s surface and
formed the crust. These rocks became the ocean floors and the land areas called shields which
were the original continents.
The heating of the earth’s interior also caused other chemicals inside the earth to rise to the
surface. Some of these chemicals formed water and other formed the gases of the atmosphere.
Over many years, the water slowly collected in low places of the crust and formed the oceans. As
land developed, rain water and rivers dissolved salts and other substances from rocks and carried
them to the oceans, making the oceans salty.
The earth’s earliest atmosphere may have contained hydrogen, helium, methane and ammonia,
similar to the present atmosphere of Jupiter. Or it may have contained a large amount of carbon
dioxide as does the atmosphere of Venus. The Earth’s earliest atmosphere probably did not
contain much oxygen. Oxygen collected gradually as the earth aged. The oxygen was originally
combined with other chemicals in rocks. The melting of these rocks need the oxygen and allowed
304 Blooming Science Book 10
it to escape to the surface. As the amount of oxygen increased, conditions on earth became
favourable for plants and animals.
Geological Time Scale
The time scale which includes the history of the earth from its origin to present is called geological time
scale. It is divided into eons. There are four eons like Hadean, Archean, Proterozoic and Phanerozoic.
The eon is divided into era, there are four main eras like Precambrian, Paleozoic, Mesozoic and
Cenozoic. The era is divided into periods and recently period is also divided into epoch. [For more
details see table in page 303]
Precambrian era (4500 MY -570 MY)
The Azoic, Archean and Proterozoic eons make up almost the
first 4 billion years (US: 4,000,000,000 years) of the Earth’s
earliest history. This length of time covers about 80 percent
of the Earth’s total history. It is often called Precambrian era.
During the Azoic eon 4.5 billion years ago to 3800 million
years ago), Earth had its very beginning. No evidence of life has been found in rocks of this era.
Rocks of the Archean eon (3800 MY - 2500 MY) contain fossils of the first and most primitive
life include different types of marble, slate and other metamorphic rocks. Fossils of the first
animals appear in rocks of the Proterozoic eon (2500 MY-570 MY). These animals include
worms, sponges, jellyfish, corals and other primitive invertebrates. Algae and bacteria also were
still plentiful.
The Paleozoic Era (570MY-250MY): [ Note : MY - million years ago ]
The Paleozoic Era began 570 million years ago and ended 250
million years ago. It included seven periods. These periods were,
from oldest to youngest: Cambrian, Ordovician, Silurian, Devonian,
Mississippian, Pennsylvanian and Permian. The Mississippian and
Pennsylvanin periods are sometimes considered a single unit called
Carboniferous period. Because coal plants like fern flourishes in this
era.
Rocks of the Paleozoic Era contain a large number and variety of
fossils. The appearance of such a great number of fossils of invertebrates suggests that much of
the earlier fossil record was destroyed by erosion at the end of the Proterozoic Era.
Plants of the Cambrian Period include water-dwelling algae from the Proterozoic era. During the
Pennsylvanian Period, there were a great variety of ferns. Some grew 100 ft high in the coal-
making swamps of the Pennsylvanian Period. The first true seed plants, the conifers are found as
fossil in strata formed during the Permian Period.
The animals of later Paleozoic periods include corals,
sea lilies, sea urchins, crayfish like animals called
euryptherids, sharks, armored fish, lungfish, amphibians,
and reptiles. Amphibians were the first air-breathing
animals with backbones to walk on land. It is the era of
amphibians because they were abundant and dominant in this
era. [Note : My-million years ago}
Blooming Science Book 10 305
The Mesozoic Era (205MY-65MY):
The Mesozoic Era began 240 million (240,000,000) years ago and ended 65 million years ago. It
had three periods. These periods were, from oldest to youngest: Triassic, Jurassic and Cretaceous.
Fossil plants of the Mesozoic Era include algae, ferns, mosses, and conifers, all of which
continued from the Paleozoic Era.
Single celled animals called protozoa lived in the warm seas of the Mesozoic Era. There
were many kinds of mollusc and fish, amphibians and reptiles also flourished. Dinosaurs,
a group of giant reptiles, lived only during the Mesozoic Era. It is the time of reptiles
because reptiles were abundant and dinosaurs evolved in this era were most powerful
and dominated all others. They extinct in cretaceous period. Dinosaurs died out completely
at the end of the era. The first warm blooded mammals appeared during the Triassic Period,
and birds appeared during the Jurassic Period.
The Cenozoic Era: (65MY-Till now)
The Cenozoic Era began 65 million (65,000,000)
years ago and is still going on. It covers the
Tertiary Period which lasted until 1.8 million years
ago and the Quaternary Period which includes the
present time. The Tertiary Period is divided into
five epochs Paleocene, Eocene, Oligocene, Miocene
and Pliocene.
The Alps, Andes and the Himalayan mountains were formed during the Cenozoic Era.
A wide variety of plants and animals that we know today came into existence during the
Cenozoic Era. Small mammals that first appeared during Mesozoic Era lived during Paleocene
Epoch. During the Eocene Epoch, ancestors of the horse, rhinoceros, and camel roamed
Europe and North America. By the Oligocene Epoch, dogs and cats had appeared along with
three-toed horses about as large as sheep. It is therefore called as age of mammals.
The earliest human fossils are in rocks of the Pleistocene Epoch, in tertiary period. Humanity’s
years on the Earth are only a brief moment among the billions of years during which the
Earth developed. But, also due to our intelligence, in the short period of time human has ruled
the earth.
Fossil
The animals and plants in the past history were trapped inside the earth. They were preserved in
one or other forms. The impressions left by these animals or plants in the soil or rocks are called
fossils. These are generally found in stones, rocks, hard soil, etc. The study of fossils is called
planetology.
The fossils can be identified on the following basis.
a. The impression of a whole or a part of any organ of dead organism remains hard in the
ground or stone.
b. The whole skeleton of some plants and animals are found in the rocks.
c. The morphology of hard parts like skeleton, teeth, bones, shoot, leaves, etc. of some
organisms are found in the ground, sand stones, etc.
d. It may be found in the form of molds and casts.
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Process of Fossil Formation
The fossil is formed by different processes which is called fossilization. Some of these processes
are:
a. Some parts of organs or entire body of an organism decay in the soil while some parts are
preserved after they are buried in the sand, mud etc. The impressions left by the body part
or organ remain in the rock, soil etc. The dead bodies of aquatic animals are more likely
to be preserved since there is a chance of formation of sedimentary rocks.
b. Because of volcano, earthquake, flooding, etc. in the earth, the animals and plants sink
into the earth’s ground,the delicate parts of these organisms decay in the soil, while other
parts remain trapped in the soil. Similarly, vacant spaces remain in places where the dead
bodies of organisms decay in the soil. The external figure of the organism is formed after
the vacant space is filled with other objects. Therefore, the body of the animal or plant
remain in hard objects in the form of impressions. The evolutionary trend of organisms
can be discovered after taking out these parts and studying them.
c. Organism are also fossilizing in the form of casts in sediments. The water inside the
sediments dissolves the hard parts, learning a hollow space in the sediments. The hollow
space is called mold, the space is then filled with minerals which hardens to form cast.
d. Replacement of minerals instead of organism body in sediment gets petrified. Fossilization
occurs in this way also.
Importance of Fossil
1. The study of fossil helps to discover the evolutionary trend of organisms.
2. The age of the rock and the life at that time can be known.
3. It supports the evolution of life.
4. They help to know about the past animal.
5. Fossils can be used as fuel like coal.
6. They help to make geological time scale.
Fossil Fuel
The most common fossil fuels are coal, mineral oil and gases. These are formed after millions of
years. Humans started these fuels from the origin of their life.
Coal
Coal is one of the fossil fuels. It lies underground in the form of thick layers. In some places they
form layers with stones and sedimentary rocks. There are different forms of coal. They are grey,
black and dark black coal.
Formation of Coal
In the carboniferous period, there were forests of coal plants (fern) in the swamp of the earth.
These plants were buried under the earth due to some natural processes like earthquake, landslide,
flood, etc. As time passes, the buried plants were covered by sediments of soil and sand along
Blooming Science Book 10 307
with water and were protected from decaying. The high temperature and pressure on the buried
plants by the sediments charge them into black residue contain carbon, hydrogen and oxygen
which is a coal. The process of formation of coal from plants inside the earth by the huge pressure
and temperature of earth is called carbonization.
S.N. Types of Colour Fossils Hardness Weathering Other Properties
Coal visible
burns with smoke,
1. Lignite Brown soft weathers loosely help
easily particles
2. Sub- black visible slightly weathers burns with less
bituminous hard easily smoke, waxy
visible does not burns with blue
weather smoke
3. Bituminous black under hard easily
hard brittle, burns
microscope does not without smoke
weather
black visible easily
4. Anthracite and under
shiny microscope
Out of them lignite is the worst and anthracite is the best type of coal.
Importance of Coal
Coal is an importance source of fuel energy. It is used at homes, factories, etc. Coal is very
commonly used in brick factories, iron factories, etc. It is also used for making coal tar, rubber
for tyre, etc.
Mineral Oil
The word mineral means 'rock' so, the oil trapped in between porous sedimentary rock is called
mineral oil. Petroleum, grease, lubricating substances, kerosene oil, etc are different forms of
mineral oil. The crude oil extracted from the earth contains different ingredients. They are refined
into different forms. About 90% to 95% of hydrocarbon is present in the mineral oil. In addition,
small amounts of oxygen, sulphur, nitrogen and other mineral substances are also present in it
as mixture.
308 Blooming Science Book 10
Formation of Mineral Oil
Sea plants and animals when died suddenly pressed under the bottom of sea and sedimentary
rock was formed above it due to geographical disorder. The substances trapped inside
went incomplete combustion. Their hard parts could not decay although their soft parts
decayed. These parts were again pressed by sedimentary rocks. Because of high pressure at
moderate temperature, scarcity of oxygen and by the action of bacteria the dead bodies were
converted into a dark liquid trapped in the pores of rocks which is called mineral oil. The
hydrocarbon compounds were formed as a result of geochemical reaction.
Crude oil is formed from the hydrocarbon compounds. It takes millions of years for the
formation of crude mineral oil. Some of petroleum products are:
Petroleum products Utility
Gas
Petroleum as a fuel gas
Gas oil and diesel oil
Kerosene as a solvent, for cleansing purpose
Lubricating oil, grease, Vaseline
Paraffin wax for ignition, diesel vehicles
Petroleum coke
as a fuel
for lubrication
for making candles, matchsticks
as a fuel
Importance of Mineral Oil
1. Mineral oil is used to run vehicles. It is also widely used in cooking fuel. Petroleum
products are used in making chemical fertilizes, insecticides, plastics, dyes, dynamites,
medicines, etc.
2. Mineral oil is used as fuel in different industries.
Blooming Science Book 10 309
A short account on geographical and biological history of the earth
Eons Eras Periods Epochs of Events in the history of life Other important events
Present cenozoic (Climates)
Quaternary Present
Holocene Human cultures Climatic zones and changes
1.8 my of season
0.5 my
Present Cenozoic Pleistocene man in stone age. human as user of Periodic continental
Tertiary 1.8 my fire and tools glaciers in north
Pliocene Cool and temperate
5.2 my Earliest man (2 my) climates away from equator
Miocene Rapid spread and development of Cooling of climate
24 my grazing mammals, angiosperms
Oligocene Earliest elephants, first modern Warm climates still widely
38 my mammal spread
Eocene Zoned climatic belts well
54 my First rhinoceros and camels established
Paleocene First primates and horses, spread of Development of climatic
65 my mammal, birds and insects belts
65 my 65 my
225 my Cretaceous Extinction of dinosaurs, first Birth of modern mountains
- flowering plant, spread of flowering Development of climatic
Mesozoic 570 my 145 my plants, marsupial mammal diversity.
Present Phanerozoic Jurassic First bird and mammals, gymnosperms
as dominating plants Culmination of worldwide
190 my - warm climate
Triassic
225 my Dinosaurs at their peak
Permian
280 my - The first dinosaurs (225 my) Worldwide tropical and
subtropical climate
Pennsylvanian
Mammal like reptiles Ice age in southern
325 my - hemisphere climates
Paleozoic Mississippian become varied
First reptiles,
345 my Uniform climates through
Devonian - Amphibians dominant on land out world.
395 my spread of coal plants Uniform climate
Rise of insects Spread of tropical seas
Silurian - Forest of coal plants
430 my
Ordovician First amphibians Broad distribution of
500 my - First forest, first insects uniform climates, Increased
Cambrian temperature
Age of fishes
570 my First air breathing animals
- - First land plants Slight climate cooling
- Trilobites at peak Wide spread flooding of
- First vertebrate (Fish) North America by seas,
Warm climate
Age of invertebrates
Marine shelled invertebrates
570 my common Climate become
Proterozoic progressively warmer
First abundant animal fossils
2500 my Marine invertebrates probably Glaciation -probably
Pre cambrian - common, few with shells (1200 my) worldwide.
Archeozoic
- Earliest plants [Marine algae] (3200
my)
Oldest rock (3500 my)
3500 my --
Azoic 4600my
4600 my
Source: Modern Biology Otto and Towle Holt, Rinehart and Winston publishers New York.
Let's Learn
1. Fossils are found in sedimentary rocks only. It is because the fossils are formed in rocks by
sedimentation of things over the dead bodies. The things which cover the dead bodies change
into sedimentary rocks in which the fossils are preserved. Similarly only sedimentary rocks
are not formed at high temperature otherwise the dead bodies could destroy.
310 Blooming Science Book 10
2. The Earth and the man were not originated at the same time. It is because the study of
fossils shows that the earth is originated about 4600 millions years ago but the human
beings were originated about 2 million years ago only. Some evidences also show that at
the time of the origin of earth, it did not have the atmosphere like the present time. Thus,
it also can be said that none of the organism was originated with the origin of the earth.
3. Mesozoic era is called the time of reptiles. It is because in this era dinosaurs like reptiles
were abundant. In the Triassic period of the era, dinosaurs were originated. They were at
the peak in the Jurassic period of the same era. In the Cretaceous period dinosaurs became
extinct because they could not adjust themselves in their surroundings.
4. Fossils are advantageous to us in many ways. It is because many of the fossils like coal
and mineral oil are used as fuel and by the study of fossils we can know about the history
of the earth and the organisms.
5. Use of fossil fuel is not so good because they are in limited amount in the earth and are
non-renewable source of energy when they are burnt as fuel they cause air pollution by
mixing some harmful gases and smoke in air.
Points to Remember
1. Earth science is the study of the nature, distribution, behavior and origin of the materials
of the earth and its atmosphere.
2. The related fields of science with earth science are: geography, geochemistry, geophysics,
paleontology, etc. It also includes astronomy, biology, chemistry and physics.
3. By the study of earth science we would know about the origin of the Earth, internal
structure of the Earth, formation of mountains, hills, lakes, rivers, causes of earthquake,
volcanoes, etc.
4. Earth science also deals with the appropriate spots for agriculture, cities, roads, mines,
water resources, etc.
5. The study of Earth science is known as geology.
6. There were great changes undergone in course of the formation of the Earth.
7. High peaks might have been below ocean a long time ago and vice-versa.
8. For the study of the origin of the Earth, it is required to study about the origin of the solar
system.
9. Planetesimal theory was propounded by George wotan in 1745 AD. According to this
theory, the Earth is formed from the hot clouds and dusts which came out from the sun due
to the sudden passage of a star nearby and condensing of the mass.
10. Nebular theory was propounded by Immanual Kant in 1755AD and elaborated and
explained by Laplace in 1796AD. According to this theory, the nebulae of the Milkyway
galaxy contracted and formed the sun and planets in course of the rotation and revolution.
11. One of the reasons that the earth is originated from the nebulae is that it is based on radio-
active elements.
12. The origin of the Earth is estimated 450 million years before. Radioactive elements such
as Uranium, Polonium and Carbon help us to estimate the age of the Earth.
13. The fossils are the impressions of the early living beings on a rocks.
Blooming Science Book 10 311
14. The early fossils tell us that the animals of early time were very primitive.
15. The life of the Earth is divided into four eras: Proterozoic era, Paleozoic era, Mesozoic era
and Cenozoic era.
16. Proterozoic era started 4 billion years ago. The animal life and plant life was in initial state
of development.
17. The Paleozoic era contains carboniferous periods also. This era ended 240 million years
before.
18. Some amphibians, reptiles and grasses were the remarkable development of this era.
19. The Mesozoic era ended 65 million years ago. The reptiles like dinosaur were the most
advanced animals in this era.
20. The Himalayas, the Andes were formed in the Cenozoic era. The origin of mammals and
human beings and seeded plants took place in this era.
21. The earth can be divided into different layers from the structural point of view: Crust,
Mantle, Outer core and Inner core.
Project Work
Make a table of different eras with the evolutionary trend and climatic condition in a chart
paper. Discuss it with your friends and keep in your classroom.
Exercise
1. Answer the following questions.
a. Enlist the hypotheses given about the origin of the earth and write a short note on
planetesimal hypothesis.
b. How was the solar system originated, according to the nebular hypothesis ?
c. How was the earth originated according to the tidal hypothesis ?
d. What is geological time scale ? What is the estimated age of the earth ?
e. Write in short about Precambrian era.
f. What do you mean by fossil? Define palentology and fossilization.
g. What are the main events of Jurassic period in the history of the earth? In which era were
the primates originated?
h. Write short notes on:
i. Palaeozoic era ii Cenozoic era
iii. Mesozoic era iv. Fossil
i. Write the differences between Mesozoic and Palaeozoic era on the basis of the
evolution of life in these different eras.
j. How are fossils formed ? Write in short how fossils are helpful to us.
k. How can we identify fossils ? What are moulds and casts ? Write the name of different
petroleum products. In which types of rocks are the fossils found ?
l. What is meant by epochs and periods ? Write the name of geological eras.
m. What is fossil-fuel? Why should we use it less?
312 Blooming Science Book 10
n. Make a list of the types of coal with their quality.
o. How was coal formed in the earth ?
p. Why is coal important to us ? Write any four uses of coal.
q. What is mineral oil ? Write a short note on the formation of mineral oil inside the earth.
r. Write the major events that occurred during Cenozoic era.
s. In which era were dinosaurs originated ? What are the periods of this era? Write
names only.
t. On what basis have scientists said human beings and the earth were not came into
existence at the same time ?
u. What are the periods of Mesozoic and Cenozoic era ? What are the chief animals
developed in those eras ?
22. Give reasons.
i. The first life must be originated in water.
ii. Coals and mineral oil are not formed at earth surface.
iii. Dinosaurs get extinct in Mesozoic era.
iv. Life was not possible in Precambrian era.
23. Differences between:
a. Coal and mineral oil
b. Mesozoic and cenozoic era
24. Choose the correct alternatives from the following options.
i. The time period of Mesozoic era is:
a. 225 MY – 65 MY b. 65 MY – Present
c. 570 MY – Present d. 570 MY – 225 MY
ii. The study of fossil is called:
a. Planetology b. Fossilization
c. Carbonisation d. All of them
iii. Which era is called the era of amphibians?
a. Mesozoic b. Cainozoic
c. Pre Cambrian d. Palaeozoic
e. All of the above
iv. In which period were dinosaurs evolved ?
a. Jurassic b. Cretaceous
c. Cambrian d. Triassic
v. The best type of coal is:
a. Lignite b. Anthracite
c. Bituminous d. All of the above
Blooming Science Book 10 313
Chapter Atmosphere and
Climate change
22
Learning Outcomes Estimated Periods: 5
On the completion of this unit, the students will be able to:
write about national and international efforts to reduce the impacts of climate change.
reconize different layers of atmosphere.
state the importance of ozone layer.
describe the effect of chlorofluorocarbon on ozone layer.
explain the green house effect in natural environment.
list out the importance and use of artificial green house.
tell the adverse effect of gases expelled by industrial pollution.
Climate Change
Terrestrial climate is dynamic. It does not remain same at the same place forever. After a regular
interval of time, it is found to have changed as in the past. Climate change is a natural event
which is caused by antropogenic and natural factors. If it is caused by natural activities like
mountain forming, volcanic eruption and continental drift, it takes a very long time. Due to it,
there are more chances of adaptation of organisms in that new environment which does not affect
their population negatively. But anthropogenic processes i.e. human activities like maximum use
of fossil fuel, deforestation, desertification, industrialization, etc. accelerate the climate change in
a short period. It causes the extinction of species and it is unfavorable to human as well. Global
warming is a result of anthropogenic factors.
Researches show that in past 100 years sea level has increased by 12.5cm and temperature
is increasing by 0.06°C per year. Scientists have estimated that by 2100 AD, the worldwide
temperature will increase by 1.8°C to 6°C and sea level will increase by 50 cm to 1m. The data
indicates a climate change.
Causes of Climate Change:
- Green house effect
- Excessive use of fossil fuels like coal, mineral oil, natural gases, etc.
- Natural phenomena's such as volcanic eruptions and earthquakes
- Depletion of ozone layer.
- Global warming
- Excessive use of harmful chemicals and non-degradable waste matters.
- Unsustainable development activities.
Effects of climate change.
- The frozen water on the poles of earth is melting.
314 Blooming Science Book 10
- Weather of all kinds is getting more extreme.
- The oceans are getting warmer, expanding and becoming acidic.
- Marine animals are suffering due to variation in temperature.
- Solar radiation is causing various kinds of skin and eye diseases like skin cancer, cataract etc.
- Many plants and animals are in the state of extinction due to the climatic change in their habitat.
- Acid rain is frequently occurring.
National efforts made to mitigate climate change
Some of the major efforts that have been made inside Nepal to reduce and adapt to climate
change are explained below.
a. Climate change policy, 2067
Climate change, also called global warming. It refers to the rise in average surface
temperatures on Earth. The primary cause of climate change is the burning of fossil fuels,
such as oil and coal, which emits greenhouse gases into the atmosphere primarily carbon
dioxide. Other human activities, such as agriculture and deforestation, also contribute to
the proliferation of greenhouse gases that cause climate change. It is essential to generate
awareness regarding ways to adapt to and reduce climate changes and its negative effects
on different sectors. It is also necessary to build the capacity of the people at various levels
regarding of climate changes. The climate changes policy 2067 was introduced in Nepal
with some objectives and policies.
b. National Communication Report
Nepal has submitted its first National Communication Report to the COP of the United
Nations Organizations protocol regarding the issue of the climate changes. This report
includes the need of study and research in various sectors like in industry, forest, health,
proper management of garbage, transportations, etc. In this report, adverse impacts of
climate changes in Nepal and ways for its adaptation, plans for capacity building to go
against climate changes and implementation of policies and ways to combat climate
change, have been mentioned. This report
c. Climate Change Adaptation Strategic Programme
Adapting to climate change means understanding what climate we are likely to experience
in the future, and creating proactive plans for how to take advantage of opportunities and
avoid and prepare for impacts. This is different than mitigation, which refers to our efforts
to limit climate change by reducing greenhouse gases. The climate change adaptation
program of Nepal has been taken a long-term program by dividing it into various sectors
like adaptation to risks introduces by climates, promotion of climate change adaptation
for vulnerable species, building a ‘capable community’ for climate change adaptation with
the active participation of the private sector, etc.
d. Local adaptation programme related to climate change
This program prepares and co-ordinates local and national level programs related to the
climate changes. It has been conducted at the community level in the rural areas. It selects
the process of climate adaptation and equi-adaptation on the basis of four theories they are
progressive, inclusive, capability and flexibility.
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e. National Adaptation Programme of Action (NAPA) to Climate Change
NAPA is a strategic tool to assess climatic vulnerability, and systematically respond to
climate change adaptation issues by developing appropriate adaptation measures. This
program was prepared by the Nepal government in September 2010 AD. The main
objective of this program is to evaluate the risk of climate changes. It has conducted 250
programs in the form of nine integrated programs.
International efforts made to mitigate climate change
The major cause of climate change is human activities and it becomes global issue of concern.
Some international efforts made to fight against climate change are:
a. United Nations Framework Convention on Climate Change(UNFCCC)
The UN family is in the forefront of the effort to save the planet. In 1992, its
“Earth Summit” produced the United Nations Framework Convention on Climate
Change(UNFCCC) as a first step in addressing the climate change problem. It has near-
universal membership. The 197 countries that have ratified the Convention are Parties to
the Convention. The ultimate aim of the Convention is to prevent “dangerous” human
interference with the climate system. The UNFCCC is a “Rio Convention”, one of three
adopted at the “Rio Earth Summit” in 1992. Nepal signed in this UNFCCC treaty in 1992
June 12. The parliament of Nepal adopted the treaty in 1994 AD.
b. United Nations Climate Change Conference
The United Nations Climate Change Conferences are yearly conferences held in the
framework of the United Nations Framework Convention on Climate Change (UNFCCC).
The first UN Climate Change Conference was held in 1995 in Berlin. The 24th conference
was held in 2017 in Germany. In 2011, Nepal prepared the climate change policy on the
basis of the UNFCCC and is acting accordingly. The 25th UN Climate change conference
was held on Poland in the month of December 2018.
c. Agenda 21
Agenda 21 is a comprehensive plan of action to be taken globally, nationally and locally
by organizations of the United Nation’s System, Government and Major Groups in every
area which human impacts on the environment.
Agenda 21, the Rio Declaration on Environment and Development and the statement
of principles for the sustainable management of forest were adopted by more than 278
governments at the United Nations Conference on Environment Development (UNCED)
held in Rio de Janerio, Brazil, 3 to 14 June 1992. The commission on sustainable
Development (CDS) was created in December 1992 to ensure effective follow-up of
UNCED, to monitor and report on implementation of the agreements at local national,
regional and international levels. It was agreed that a five year review of ‘Earth Summit’
program would be made in 1997 by the United Nations General Assembly meeting in
special session.
The full implementation of Agenda 21, programme for further implementation of Agenda
21 and the commitments to the Rio principles, were strongly reaffirmed at the world
316 Blooming Science Book 10
summit on Sustainable Development (WSSD) held in Johannesburg, South Africa from
26 August 3 September 2002.
d. Kyoto Protocol :
Source: http://unfccc.int/kyoto_protocol/items/2830.php
The Kyoto Protocol is an international agreement linked to the United Nations Framework
Convention on Climate Change, which commits its Parties by setting internationally
binding emission reduction targets.
Recognizing that developed countries are principally responsible for the current high
levels of GHG emissions in the atmosphere as a result of more than 150 years of industrial
activity, the Protocol places a heavier burden on developed nations under the principle of
"common but differentiated responsibilities."
The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and entered into force
on 16 February 2005. The detailed rules for the implementation of the Protocol were adopted
at COP 7 in Marrakesh, Morocco, in 2001, and are referred to as the "Marrakesh Accords." Its
first commitment period started in 2008 and ended in 2012. In Doha, Qatar, on 8 December
2012, the "Doha Amendment to the Kyoto Protocol" was adopted. The amendment includes:
i. New commitments for Annex I Parties to the Kyoto Protocol who agreed to take on
commitments in a second commitment period from 1 January 2013 to 31 December
2020;
ii. A revised list of greenhouse gases (GHG) to be reported on by Parties in the second
commitment period; and
iii. Amendments to several articles of the Kyoto Protocol which specifically referenced
issues pertaining to the first commitment period and which needed to be updated
for the second commitment period.
On 21 December 2012, the amendment was circulated by the Secretary-General of the
United Nations, acting in his capacity as Depositary, to all Parties to the Kyoto Protocol in
accordance with Articles 20 and 21 of the Protocol.
During the first commitment period, 37 industrialized countries and the European
Community committed to reduce GHG emissions to an average of five percent against
1990 levels. During the second commitment period, Parties committed to reduce GHG
emissions by at least 18 percent below 1990 levels in the eight-year period from 2013 to
2020; however, the composition of Parties in the second commitment period is different
from the first.
e. Measures to reduce Green house gases (GHG) on the basis of Kyoto Protocol :
Under the Protocol, countries must meet their targets primarily through national measures.
However, the Protocol also offers them an additional means to meet their targets by way
of three market-based mechanisms. The Kyoto mechanisms are:
i. International Emissions Trading (IET)
ii. Clean Development Mechanism (CDM)
iii. Joint Implementation (JI)
The mechanisms help to stimulate green investment and help Parties meet their emission
targets in a cost-effective way.
Blooming Science Book 10 317
Ways to minimize Climate Change
1. Enhancing use of renewable and perpetual natural resources.
2. Prohibiting high use of green house gases like CFCs which is responsible for depletion of
ozone layer.
3. Conducting development activities in a sustainable way.
4. Prohibiting use of nuclear weapons.
5. Reducing use of non-degradable matters.
6. Removing old vehicles and awaring the people for using public vehicles.
7. Afforestation programme should be conveyed.
Atmosphere
The earth is surrounded by the thick gaseous envelope called air. The envelope of air that
surrounds the earth all around is called atmosphere. It extends upto a height of 1600 km from the
earth surface. The atmosphere is a mixture of various gases and water vapour, the composition
and ratio of which vary with altitude. It mainly consists of nitrogen (78 percent) and oxygen (21
percent). The other gases like argon, carbon dioxide, hydrogen, helium, ozone etc make up only
one percent. Besides these gases, atmosphere contains variable amount of water vapours, dust,
smoke and other impurities. Among the many gases, carbon dioxide is the green house gas and it
is the raw material for photosynthesis. Without oxygen living organisms, both plants and animals
cannot survive. The earth’s gravitational force holds the atmosphere around it. About 99% of the
atmosphere lies below an altitude of 30km.
Atmosphere maintains the average temperature of the earth and also protects the earth from the
harmful ultra-violet rays coming from the sun. It prevents the earth from extra cooling due to
heat radiated by the earth.
The density of the atmosphere shows a sharp decrease with increasing altitude. In other words,
it is denser near the earth’s crust and becomes thinner and thinner as we go higher up. On the
basis of varying density, altitude and temperature conditions, the atmosphere is divided into five
distinct layers. They are troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Troposphere
It is the lowermost layers of atmosphere. The layer of atmosphere near the surface of the earth
in which living organisms live is called the troposphere. The average thickness of this layer is
about 16 kilometers. Its thickness varies between 8-10 km at the poles and 16 km at the equator.
The temperature falls in the troposphere by about 6.5oC for every kilometer rise in altitude. The
rate of temperature decrease slows down up to the tropopause. Most of the weather forming
phenomena occur in this layer. So, this layer is important for meteorologist.
The dust and smoke emitted from the industries and construction works affect this layer. This
layer consists of most of carbon dioxide, water vapour and dust particles. This layer receives heat
indirectly as the sun’s heat re-radiate from the earth’s surface. 95% of the air of the atmosphere
is found in this layer. All the atmosphere’s water vapour is available in this layer which therefore
enclosed essentially all the storms and precipitation of the earth.
The upper boundary of the troposphere is called tropopause.
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Staratosphere (Ozonosphere) 10000km
The layer of atmosphere above the troposphere is called Exosphere
stratosphere. It is extended from 16-50km above the
earth surface. The atmosphere is thin and the water is not 720km
disturbed in this layer. This layer is free from clouds and Thermosphere
other weather phenomena.
The temperature starts increasing up to the height of 50 km Mesosphere 80km
within stratosphere. The temperature changes from -55oC to Stratosphere 50km
-2oC in this layer. Troposphere 15km
Major component of this layer is ozone, hence this layer of
atmosphere is called ozonosphere. The ozone absorbs 99%
of the ultraviolet rays of the solar radiation. The increase of
temperature within stratosphere is due to the formation of
heat by a cycle of chemical changes in the ozone layer which
converts all the absorbed ultraviolet rays to heat. Fig: Layers of Atmosphere
The stratosphere contains very less water vapour, so cloud
formation and rain do not occur. Although cloud, cirrus may be formed at the lower level of this layer.
The air movement in this layer is almost horizontal. Almost all the jet planes fly in this layer to avoid
the bumpy air pockets of the troposphere.
The upper boundary of stratosphere is stratopause.
The stratosphere ends at the stratopause. The air of this layer is very thin and the oxygen
concentration is also less to form ozone.
Mesosphere
This layer starts from the stratopause. It extends nearly upto the height of 80 km from the
earth’s surface. The temperature decreases upwards and reaches upto -2 to -100oC at its upper
boundary, which is called mesopause. The mesopause is the region of minimum temperature in
the atmosphere. The air in this layer is thin.
It is the coldest layer of atmosphere because it has very less ozone to absorb the sun’s ray.
Mesosphere has strong wind blows. Trails of hot gases left by meteors in the mesosphere can be
seen from the earth surface.
Thermosphere (Ionosphere)
It is the fourth layer and lies above the mesopause. It extends nearly from about 80 km to 720 km
from the earth’s surface. The temperature in this layer increases with the increase in altitude.
The temperature varies from -100oC to 1500oC. In this layer the density of air is very low and
the gases present are in very small amount. The lower atmosphere contains nitrogen and oxygen
molecules and upper surface has hydrogen and helium gas. These molecules are broken down
into atoms by intense solar radiation and the atoms are further ionized producing electrically
charged particles called ions. Radio waves transmitted from the earth are reflected back to the
earth from this layer and thus helps in communication.
It is also known as ionosphere because of the ionization of the lower part of the thermosphere.
Blooming Science Book 10 319
Exosphere
The exosphere is the uppermost layer of the atmosphere. It extends from 720 km and gradually
merges with the outer space. Actually, it is the outer fringe of the earth’s atmosphere except that
of hydrogen and helium. Its temperature varies from 1200oC to 6000oC. Due to abundance of
helium, this region is also known as helium zone. The air is very rarefied and the particles present
in this layer are moving with very high speed and even earth’s gravity has no effect on them.
Ozone Layer
Ozone layer is present in troposphere and stratosphere. Ozone is a molecule of three oxygen
atoms occurring naturally in the atmosphere. Almost 90 percent of all ozone in the atmosphere
is in the stratosphere. It is pale blue gas. It absorbs about 99% of harmful ultra violet radiation.
This layer is regarded as a protective layer. So it forms protective shield thereby preventing
the harmful ultra violet radiation from the sun reaching the earth. The ultraviolet radiation is
absorbed by the ozone layer so, the temperature of the stratosphere is high. This ozone layer
plays an important role in maintaining balance of temperature and weather.
Ozone is naturally formed when ultraviolet radiation strikes the stratosphere. These UV
radiations split-up oxygen molecule into individual oxygen atoms. Each oxygen atom combines
with molecular oxygen to form ozone.
O2 UV O + O (atomic oxygen) (Nascent = Newly born)
O2 + O UV O3
Ozone layer absorbs the ultraviolet rays of wave length lesser than 340mm. They break into oxygen
gas and nascent oxygen. Oxygen molecule is formed by the combination of two nascent oxygen atoms.
O3 UV rays O2 + O (atomic oxygen)
O + O UV rays O2
Ozone is also formed in the lower atmosphere due to artificial activities, especially due to catalytic
reaction of nitrogen oxides and hydrocarbons related industries and automobiles.
NO2 NO + O
Atomic oxygen reacts with molecular oxygen to form ozone.
O2 + O O3
Depletion of Ozone Layer
Mainly chemicals released by automobiles, industries, fossil fuels burning etc. are responsible for
ozone depletion. Chlorofluorocarbons (CFCs) is the most responsible compound for ozone layer
depletion in the atmosphere. Methyl chloroforms, carbon tetrachloride and methyl bromides are
other ozone depleting gases. These substances are called ozone depleting substances. Over the
past 10 to 15 years, there has been a large and unexpected loss of ozone in the stratosphere
specially in Antarctica region.
Chlorofluoracarbon is a chemical compound containing carbon, hydrogen, chlorine and fluorine
atoms. It is an industrial chemical. Chlorofluorocarbon gas was invented by Thomas Midgley 1930
A.D. CFCs are used in aerosols, foams, refrigerators, air conditioners, solvents, fire extinguishers
etc. Since 1955 A.D. their rate of production has increased progressively and used cooling gas in
refrigerators because it is cheaper than ammonia gas which is also used as cooling gas.
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CFC is an important green house gas too. It can absorb much more radiation than CO2. Therefore
it is contributing much more in greenhouse effect as well as in ozone layer depletion. It is also
responsible for global warming.
It has been clear that the ozone concentration of the earth’s atmosphere is thinning out largely
due to increased use of CFCs by humans. CFCs are used in refrigerators, aerosols spray cans, air
conditioners, plastics and engines of high altitude planes. These CFCs move slowly upward to
the stratosphere. Here, they are decomposed by powerful UV rays, releasing the chlorine atoms
(nascent chlorine). The nascent chlorine reacts with ozone molecule (O3), remove the extra atom of
oxygen which makes ozone. Thus, it destroys the ozone layer. It is estimated that a single chlorine
atom can destroy more than 100,000 ozone molecules. It is illustrated by the following equation.
CFCl2 UV rays CF Cl + Cl2 (atomic oxygen)
Cl + O3 UV rays ClO +O2
2ClO UV rays 2Cl + O2
CL + CFCl2 UV rays CFCl3 (again)
Now a huge amount of CFCs are being used and released to atmosphere as pollutant. The presence
of CFCs in atmosphere was detected in 1974 A.D. CFCs have adverse effect on the ozone layer.
Ozone Hole: An ozone hole is the region of space in the stratosphere where the amount of ozone
(O3) content has been reduced drastically. A large number of such holes have been found in the
stratosphere. For example, a large ozone hole was reported over Antarctica where ozone content
dropped by 30 percentage from its normal value.
When the ozone holes are created, the high frequency ultraviolet radiations coming from the
outer space directly enter into the stratosphere and cause many adverse effect on the living
organisms. A hypothetical ozone hole is illustrated in the figure.
In 1985’s the existence of a hole in ozone layer over Antarctic was discovered. It is more exactly
a drastic thinning of the ozone layer. In 1989 AD, the existence of a second hole over the Arctic
region has been confirmed.
Effects of Ozone Layer Depletion
The depletion of ozone layer allows more of the ultraviolet rays on the surface of the earth. The
depletion of ozone layer has been taken seriously. Some of the effects of ozone layer depletion
are as follows:
1. Thinning of ozone layer will let through more UV rays which damage plants and animals.
2. It causes skin cancer, stoppage of tissue growth. The UV absorbed by cornea and lens can
lead to develop cataracts and photokeratitis.
3. Ozone causes the global warming of the earth’s that threatens increased melting of polar
ice caps by which flooding of coastal region occurs.
4. It causes mutation in animals and effects the fertility of animals.
Blooming Science Book 10 321
Protection of ozone layer depletion
1. By banning the production and use of CFCs.
2. By finding the alternatives of CFCs.
3. By bringing awareness of ozone depletion in people.
4. By replacing fossil fuels with alternative sources of energy.
5. By reducing the use of nitrogenous fertilizers.
6. Filtre for green house gases in vehicles should be used. It controls their mixing in atmosphere.
Green House Effect
The earth is surrounded by its atmosphere. The atmosphere contains some such gases which
have capacity of absorbing the heat reflected from the earth's surface. The main gases having
this property are carbon dioxide, nitrous oxide, methane and ozone. They are called greenhouse
gases. The greenhouse gases are extended up to the height of 100 kilometers from the earth's
surface.
We know that the source of heat on the earth is the sun. From the sun, energy comes in the form
of light. When the solar energy strikes the earth's atmosphere, about 25% of it is reflected back
to the atmospheric components like ozone layer. Only about 50% of the total solar energy is the
form of visible light incidents on the earth's surface. About 85% of the energy arrived on the
earth's surface is absorbed by soil, water, plants, rocks, snow and sand of deserts and the rest 15%
is returned back into the atmosphere. The green house gases absorb heat and block it from going
again into space. It is called green house effect.
Thus, greenhouse effect is a process by which thermal radiation from a planetary surface is
absorbed by atmospheric greenhouse gases and re-radiated in all directions.
Greenhouse effect makes all living beings able to survive on the earth. It helps to maintain a
suitable temperature on the earth. But some of our activities are interrupting the natural process
due to over population, industrialization, deforestation and urbanization.
Greenhouse effect makes all living beings able to survive on the earth. It helps to maintain a
suitable temperature on the earth. But some of our activities are interrupting the natural process
due to over population, industrialization, deforestation and urbanization.
All the above events support the increment of the amount of greenhouse gases in the atmosphere
which leads to over greenhouse effect which harms us in different ways.
The main causes of increasing greenhouse gases in the atmosphere are given below:
1. Volcanic eruption is a natural process which increases carbon dioxide in the atmosphere.
2. Jungle fire releases carbon dioxide gas in atmosphere.
3. Deforestation reduces the use of carbon dioxide by plants in the process of photosynthesis
which increases its concentration in the atmosphere.
4. Different types of vehicles and machineries which use fossil fuel release carbon dioxide
nitrous oxide, etc. in atmosphere.
5. Water vapour is also a greenhouse gas which is formed by the effect of the heat of the sun
on the surface water.
6. Due to urbanization, industrialization and over population, the use of fossil fuel is
increasing which forms greenhouse gases in the atmosphere.
7. The process of decaying sewage, dead plants and animals release methane in the atmosphere.
322 Blooming Science Book 10
Impacts of greenhouse effect:
1. It causes global warming.
2. It causes climate change.
3. Some greenhouse gases may cause acid rain.
4. It decreases forest and wildlife.
5. It affects water cycle and cultivation system.
6. It causes the ice of the Himalayan regions and polar regions to melt which increases sea level.
7. It may cause skin and eye diseases.
8. It supports the spreading and growth of harmful insects.
Activity-1
In your opinion, what should we do and we should not do to minimize the emission of green
houses in the atmosphere? Make a list.
The Earth is a Natural Green House
Earth’s atmosphere acts like the
glass of a greenhouse. Different Some heat energy
gases such as nitrogen, oxygen, escapes into open space
carbon dioxide, methane, nitrous
oxide etc. are present in the
atmosphere. Nitrogen and oxygen SUN Some heat energy is
do not trap sun’s radiation. radiated back by the
Carbon-dioxide gas and methane greenhouse gases.
are the greenhouse gases. They
trap the sun’s radiation. Heat that
is normally re-radiated back into Trapping of heat energy by greenhouse gases
space by the earth is absorbed
(Greenhouse effect)
by these gases and heat the troposphere. Greenhouse effect received its name because the earth’s
atmosphere acts much like the glass of the greenhouse. The sunlight enters a greenhouse through the
glass and heats the interior. The roof and walls block the escape of the heat.
Greenhouse effect is warming of the earth’s surface that occurs due to the trapping of the sun’s heat
by the earth’s atmosphere. This effect raises the temperature of the earth and also changes weather
and climate over green house effect is not good for the living organism. Without this effect, the
average surface temperature of the earth would be less than the present normal temperature.
In the passed 100 year the earth’s temperature is increased by 0.74°. In this way from 1977 AD
to 1994 AD the temperature of the earth is increased at the rate of 0.06°C per year in average. It
is causing global warming. It is found that the temperature of the polar region is increasing more
than that of the equatorial region. Similarly temperature of high peaks of mountain is increasing
by more than in Terai and mid mountainous regions. It is reducing the water resources of river
by melting the snow faster. The following precautions should be taken to face the adverse effects
of green house effects.
1. Our dependence on fossil fuel energy should be reduced by using alternative energy
sources. It helps to produce less green house gases.
2. Reforestation should be conducted as mission all over the world as plants absorb CO2
elements from the atmosphere.
Blooming Science Book 10 323
Artificial Greenhouse
Greenhouse is a building in which plants can be grown throughout the year. Its roof and walls
are made of green glass or plastic. So greenhouses are sometimes called glasshouses. It provides
heat, light and moisture essential for the growth of the plants.
Sun
Incident heat Transparent glasses
from the sun
Heat reflected by the
surface of green house
Plant
Fig: A Green House (Artificial)
A green house is a form of controlled environment for the agriculture because the light, moisture,
temperature and other essentials for the plant growth is regulated there. The roof of green house
is made slanted as to allow more solar radiation.
The sun’s heat passes easily through the glass and retains much of the heat inside. The glass
keeps the greenhouse warm by trapping heat from the sun. The temperature inside the greenhouse
is more than outside. Different ornamental plants and vegetables such as cucumber, lettuce,
tomatoes are grown in greenhouses. These plants can be grown out of their normal growing
seasons in greenhouses. In other words, summer plants can be grown in winter.
Disadvantages of the exessive green house effect are:
1. Global warming is caused by the green house effect. It influences forests directly. The
plants found at tropical regions are also seen in the temperate region gradually. The global
warming may cause the melting of snow at polar region. It may increase sea level by
which many islands may be disappeared in ocean.
2. Agriculture system is badly affected by the over green house effect.
3. Water cycle is also affected by the over green house effect.
4. Due to the change in temperature on the earth, many diseases of skin and eye will be caused.
5. It is causing adverse effects on ecosystem.
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Global Warming
Different vehicles and factories emit harmful gases like sulphurdioxide, carbonmonoxide and
chlorofluro carbon that make a layer which permits the ultraviolet ray from the sun penetrate into
the earth but they (rays) don’t escape from the earth. Due to this, the temperature of the earth
increases and animals and plants are severely affected. This is called global warming.
Industrial Gases
There are many industries which play vital role for air pollution. Many toxic gases, lead, heavy
metals, complex organic compounds are released as the by-products of industrial processing.
Sulphur dioxide, carbon dioxide, carbon monoxide and nitrogen oxide are released from different
industries. They are the major air pollutants.
The main fuel used in industries is petroleum. In many industries petroleum is used as raw
materials also. The petroleum forms CO2, CO and SO2. They also produce other toxic gases,
mercury, cadmium and arsenic. Cement industries form SO2, NO, carbon monoxide and dust
particles. Brick industries form SO2, NO2, carbon, hydrocarbons and dust particles. Likewise
sugar industries, distilleries, textiles, leather industries, matches industries, soap industries, paint
industries, polythene industries etc. also liberate many harmful gases. All of the gases mentioned
above are called industrial gases. They mix in air as pollutants and cause air pollution.
Sulphur dioxide is released artificially due to human activities such as melting of sulphide-
containing ores, combustion of sulphur-containing fuels such as coal and oil, petroleum refining.
In the atmosphere, SO2 does not remain in the gaseous state for long time, but very soon it reacts
with oxygen to form sulphur trioxide and then with water to form sulphuric acid.
2SO2 + O2 2SO3
SO3 + H2O H2SO4
So formed sulphuric acid produces acid rain. The acid rain increases the acidity of streams,
destroying the aquatic life. The acid rain also erodes the building materials as limestone (marble),
the slate are used in roofing and deterioration of statues.
Effects of Industrial Gases
The major effects of the gases and materials left by industries are:
a. Acid Rain
The rainfall with its pH lesser than 7 is called acid rain. Due to industrialization and
urbanization gases like carbon dioxide, sulphur dioxide and nitrogen oxide are released
in the atmosphere. When they combine with water vapour in the atmosphere, they form
different types of acids like carbonic acid, nitric acid, sulphuric acid, etc. When such acids
come on the earth's surface with rain water, it is called acid rain.
Examples are:
H2O+CO2 → H2CO3 (Carbonic acid)
H2O+NO2 → H1NO3 (Nitric acid)
H2O+SO2 → H2SO3 (Sulphurous acid)
Blooming Science Book 10 325
Causes of Acid Rain
The main causes of acid rain are as given below:
1. Industrialization is the one of the main causes of acid rain which emits the gases
that can from acids in the atmosphere.
2. Different types of vehicles which consume fossil fuels also support acid it degrades
the quality of soil by making it acidic. In such soil a good yield is not found.
Effects of Acid Rain
1. It erodes metallic and rocky monuments, temples and other heritages.
2. It reduces forest.
3. It imbalances land and water ecosystems.
b. Many of the gases left by industries are green house gases and they cause global warming.
c. These gases form photochemical smog which causes eye itching and negative effects
on plants’ growth. The smog reduces the transparency of the atmosphere and it creates a
problem to pilots in landing of planes.
d. Some of the gases left by industries also cause ozone layer depletion.
e. The materials given off by industries show an adverse effect on the human health in
following ways:
i. Dust causes diseases of respiratory system.
ii. Carbon monoxide reduces the efficiency of haemoglobin.
iii. Oxides of nitrogen cause lung diseases.
iv. Sulphur dioxide causes diseases of respiratory system, headache etc.
Let's Learn
1. Green house effect is advantageous because it maintains the suitable temperature of the earth
at days and nights. In the presence of suitable temperature only the living things can survive.
2. Over green house effect is disadvantageous. It may affect the water cycle system badly. It
may spread many types of diseases and increases harmful insects. It reduces crop yielding
and changes the climatic pattern.
3. There is warm inside a greenhouse. It is because the glass used in the construction of green
house allows passing short waves only through it. When the short waves of the sun strike
on the earth surface, they change into infrared radiation or long waves and they cannot
escape out easily through the glass. It makes warm inside the glass house.
4. The atmosphere makes it possible for the living thing to survive on the earth. It is because
the atmosphere provides the suitable temperature and it contains many essential things for
life. Some such things are nitrogen, oxygen, carbon dioxide and water vapour. Similarly
it has ozonosphere, which protects the living things from the harmful effects of ultraviolet
rays of the sun.
5. Troposphere is influenced at the maximum by the human activities. It is because the
troposphere is the lowermost layer of the atmosphere in which we live. We exchange
nitrogen, oxygen, carbon and water like biogeochemical from the nature.
6. Temperature decreases with altitude in troposphere. It is because the sun rays enter in the
326 Blooming Science Book 10
atmosphere in the form of short waves. They change in to long waves after striking on the
body or the earth. The heat reflected by the earth surface makes the air warm. Due to this
reason the troposphere is heated from lower surface to its upper surface.
7. Temperature increases with altitude in stratosphere. It is because the layer of ozonosphere
found in it, absorbs, the solar radiation at the upper surface which makes the upper surface
warmer than lower surface.
8. Oxides of nitrogen also cause ozone layer depletion. It is because, in the presence of
Ultraviolet rays, they react with ozone and form O2 and NO2 . NO2 again attacks on ozone
to form N2O3 and O2. The form of a chain the chemical reaction continues and it causes
ozone layer depletion. It is illustrated by the following equations.
NO + O3 UV rays NO2 + O2
2NO2 + O3 UV rays N2O3 + 2O2 etc
9. HCFs must be used instead of CFCs because it doesn't deplete ozone layer as it has no
chlorine.
Points to Remember
1. Greenhouse effect is a process by which thermal radiation from a planetary surface is
absorbed by atmospheric greenhouse gases and re-radiated in all directions.
2. Climate change is a natural event which is caused by antropogenic and natural factors.
3. The rainfall with its pH lesser than 7 is called acid rain. Due to industrialization and
urbanization gases like carbon dioxide, sulphure dioxide and nitrogen oxide are released
in the atmosphere.
4. The temperature of the earth increases and animals and plants are severely affected. This
is called global warming.
5. Environmental conservation can be defined as all those activities which are conducted
with the aim of preserving the various components of the environment in good state for
our future generation.
6. The process of cleaning our environment is called environmental sanitation.
7. To reduce the pollution of the environment, we should use 3Rs formula, the 3R indicate
reduce, reuse and recycle.
8. In green houses the temperature is changed after the entry of solar radiation which is
stored there.
9. Chlorofluorocarbon (CFC), sulphur dioxide, carbon dioxide, carbon monoxide, nitrous
oxide and methane are mainly responsible for ozone layer depletion.
10. Green house effect is caused by increased CO2 and other gases present in the atmosphere.
These gases make the earth warm. But excess of green house gases may increase the
global temperature which is called global warming.
11. The air pollutants like the oxides of sulphur, oxides of nitrogen and halogens are released
into the atmosphere where they react with water vapour to form acids. These acids mix
with rain and fall as acid rain.
12. The earth’s atmosphere is divided into five layers according to difference in temperature
beginning from the earth’s surface.
13. Troposphere is the lowest part of the atmosphere where living beings live. It extends up to
an altitude of 16 km above the earth’s surface.
14. Stratosphere is the layer above troposphere. It extends up to 50 km above the earth’s
surface. Ozone is the major component of this layer.
Blooming Science Book 10 327
15. Mesosphere extends up to 80 km above the earth’s surface. It is the coldest region of
atmosphere. Wind blows at a very high speed in this layer.
16. Thermosphere extends from an altitude of about 80 km to 720 km.
17. Ozone is the special form of oxygen formed in the stratosphere by the influence of
ultraviolet rays on oxygen gas.
18. Exosphere is the uppermost layer of the atmosphere. It extends beyond 720 km and
gradually merges with the outer space.
19. Ozone layer begins from the upper layer of troposphere. It absorbs harmful radiations
coming from the sun.
Project Work
Make an artificial green house by using polythene sheets and bamboo / wooden sticks in
winter season. Measure the temperature of outside environment and inside the construction.
Find out the difference and discuss with your friends to conclude the reason of difference of
temperature outside and inside.
Exercise
1. What is called green house effect?
2. What are the major causes of increasing green house gases in the atmosphere?
3. Write any 5 impacts of green house effect.
4. What is called climate change?
5. Write any 4 causes of climate change.
6. What are the major effects of climate change?
7. What are the main causes of acid rain?
8. What is environmental sanitation? What do you mean by 3Rs concept?
9. What are the national efforts made to stop climate change?
10. List some international efforts made to reduce climate change.
11. List some methods to conserve the environment.
12. In artificial green house summer vegetables can be grown even in winter, why?
13. What is an acid rain? How does it affect us?
14. Green house effect is both advantageous and disadvantageous to us. Justify your answer.
15. What is atmosphere? State the importance of the atmosphere.
16. What are the various layers of atmosphere? Describe each layer in short.
17. What is the function of ozone in the atmosphere?
19. What are the effects of depletion of ozone layer in aquatic animals and the global
temperature?
20. Distinguish between troposphere and stratosphere.
328 Blooming Science Book 10
21. Answer in short:
a. Name the layer of the atmosphere which reflects radio waves.
b. Name the layer of the atmosphere which lies closest to the earth’s surface.
22. Consequences like skin burn and skin cancer were observed when sunbath is taken on
earth’s surface. Answer the following questions on the basis of it:
a. What is the cause of it?
b. What happens to the environment at this condition?
c. What is to be done to be safe from the above condition?
23. What are the two effects of pollution caused by industrial gases?
24. Sketch the diagram showing different layers of atmosphere.
25. Give reasons-
a. We should conserve ozone layer.
b. The use of CFCs must be reduced.
c. Troposphere is affected badly by human activities.
d. In stratosphere, temperature increases with altitudes.
e. Thermosphere is important for communication.
f. Troposphere is important for meteorologist.
g. Long journey plane fly at lower level of stratosphere.
h. The roof of green house is slanted.
26. Choose the correct alternatives from the following options.
i. Which layer is mostly affected by human activities?
a. Mesosphere b. Thermosphere
b. Stratosphere d. Troposphere
ii. The hottest layer of atmosphere is:
a. Exosphere b. Thermosphere
c. Ozone d. All of them
iii. What is the full form of CFCs?
a. Chlorofluorocarbon b. Carbon Fluoride Carbon
c. Chloride Fluoride Carbon d. All of the above
iv. Kyoto protocol was adopted on:
a. 1998 AD b. 1990 AD
c. 1997 AD d. None of them
v. The main cause of acid rain is:
a. Oxide of carbon b. Oxide of nitrogen
c. Oxide of sulphur d. All of the above
Blooming Science Book 10 329
Chapter The Universe
23
Lesson Objectives Estimated Periods: 4+1
On the completion of this unit, the students will be able to:
describe the shape and structure of solar system with diagram.
define light year and astronomical unit.
explain eight planets with their moons.
tell about galaxies, comets, meteors etc.
describe constellations with diagram.
analyze sign of zodiac with scientific facts.
differentiate between natural and artificial satellites.
Introduction
The universe is commonly defined as the totality of everything that exists, including all matter
and energy, the planets, stars, galaxies and the contents of the intergalactic space. The words
or terms cosmos, the celestial sphere, world and nature are used in place of universe. Scientific
observations of earlier stages in the development of the universe, which can be seen at great
distances, suggest that the universe has been governed by the same physical laws throughout
most of its extent and history. There are various multiverse theories, in which physicists have
suggested that our universe is one among many universes that exist.
All the aggregate of all existing things or the whole creation embracing all celestial bodies
(Heavenly bodies) and all of the space is called the universe.
Solar System
The sun with other heavenly bodies such as eight planets, satellites, three currently known dwarf
planets, asteroids, comets, meteors, (interplanetary dust) dust particles scattered between the
planets etc. which revolve around the sun form a solar system. The sun is the centre of the solar
system. The planets and all other members of the solar system revolve around the sun in closed
orbits. The sun holds them together by its great gravitational pull.
Units of Measuring Distance in the Universe
The universe is so vast that it is not convenient to measure the distance in metre or in kilometer.
Hence, astronomical unit, light year and parsec are used to measure the distance in the universe.
Astronomical unit: It is defined as the distance between the sun and the earth and
its value is about 1.5 × 1011m. This unit is suitable for measuring the distance of the
planets and satellites in solar system. 1'' arc
1AU = 1.5 × 1011m
Light year: It is defined as the distance travelled by light in Earth Earth's orbit
one year. Its value is about 9.5 × 1015m. 1AU Sun
330 Blooming Science Book 10
Note: Velocity of light = about 3 × 108m/s
[1 year = about 365.25 days, 1 day = 24 hr, 1 hour = 60 min and 1 minute = 60 seconds.]
The distance covered by light in one year = 365.25 × 24 × 60 × 60 × 3 × 105m
= 9.46 × 1015m or about 9.5 × 1015m
∴ 1 light year = 9.5 × 1012km = 63240 AU
Parsec: The term parsec comes from the words parallax and second. It is defined as
the distance at which the mean radius of the earth’s orbit subtends an angle of one
second of arc. It is equal to 3.26 light years.
1 Parsec = 3.26 light year = about 3.1 × 1016m = 206265 AU
Some distances in the universe are mentioned below
Light year Parsec
1. Proxima centauri 4.3 1.31
2. Sirius 8.6 2.63
3. Vega 26.5 8.12
4. Length of Milky Way 105 3.06 × 104
5. Thickness of milky Way 8 × 104 2.45 × 104
6. Distance between the sun and the galactic centre 2.5× 104 7.6 × 103
7. Distance between the Milky Way and the Andromeda 2 × 106 6.1 × 105
The Sun
The sun is a star around which the earth and other planets revolve. It is the largest body in our solar
system with a diameter of about 13,82,400 km. The volume of the sun is about 12,99,370 times the
volume of the earth. Still it is a medium-sized star of average brightness in the Milky way galaxy. It
appears to be larger and brighter in the sky because it is nearer to the earth. It is at distance of 1.5 ×
108 km from the earth. Light with the velocity of 3 × 108 m/s takes nearly 8 minutes and 20 seconds
to reach the earth.
Sun emits visible light, infrared ray, ultraviolet rays, x-rays, radio waves and other electromagnetic
radiations. Streams of gaseous charged particles named plasma are continuously emitted in the
form of solar wind from its surface. The velocity of solar wind is about 500 kilometers per
second.
The sun revolves around the centre of its galaxy and also rotates in its own axis. The sun appears to
move from east to west in the sky. It happens because the earth rotates on its axis from west to east.
The centre of galaxy is called galactic centre and time taken by sun to revolve round the galactic
centre is called cosmic year. It is 2.5 × 104 light year far from the centre of milky way galaxy.
It takes 200-300 million years to make one revolution. Table given below summarizes some of the
information about the sun.
Statistics of the Sun
Distance from the earth 1.5 × 108 km
Apparent diameter 1.29 × 109 m
Volume 12,99,370 times that of the earth
Blooming Science Book 10 331
Mass 2 × 1030 kg (329,390 times that of the earth)
Density 1.42 gm/cubic centimeter
Temperature (at the surface) 5,500o Celsius (5800 k)
Temperature (at centre) 15,000,000o Celsius
Solar constant 1358 w/m2
Pressure at centre 2 × 1012 Pa
The Planets
The planets are dark, solid or gaseous bodies that revolve round the sun in closed elliptical paths
called orbits. Planets have no light of their own. Most of them appear to shine only because they
reflect light that they receive from the sun. Since the planets are much nearer than the stars, they
appear to be big. They revolve round the sun from west to east. So the relative positions of the
planets keep changing day by day.
The International Astronomical Union (IAU), the official scientific body for astronomical
nomenclature, currently defines “planet” as a celestial body that, within the Solar System
1. is in orbit around the sun,
2. has sufficient mass for its gravitational strength to give it a spherical shape.
3. shapes should be round (spherical)
4. is in orbit around a star or stellar remnants.
5. One's orbit must not cross the orbit of others.
Under the IAU’s definition, our solar system is considered to have eight planets. Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto is very small and fails to fulfil to fulfil
the last statement as it crosses the orbit of Neptune. So, it is kept in the group of dwarf planet.
There are eight planets including the earth. These planets in the order of increasing distances
from the sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Out of eight
planets of the solar system, five planets, Mercury, Venus, Mars, Jupiter and Saturn can be seen
from the earth without the use of telescope.
Venus
Sun
Mercury Earth Mars Jupiter Saturn Uranus Neptune
Records in the Solar System
1. The largest planet Jupiter
2. Planet nearest to Sun Mercury
3. Planet nearest to Earth Venus
332 Blooming Science Book 10
4. The brightest planet Venus
5. Planet with maximum satellites Jupiter
6. Heaviest planet Jupiter
7. The green planet Earth
8. The red planet Mars
9. Earth’s sister Venus
The planets revolves around the sun in the same direction; anti-clockwise as seen from over the
sun’s north pole. The period of one revolution of the planet’s orbit is known as its year. A planet’s
year depends on its distance from the sun; the farther a planet is from the sun, not only the longer
the distance is must travel, but also the slower its speed, as it is less affected by the sun’s gravity.
All the planets also rotate around axes at their centres. The period of one rotation of a planet is
known as its day. Most planets rotate as they revolve in a counter-clockwise direction. Venus is
the only planet that rotates clockwise.
Planets are grouped into inner or terrestrial and outer planets. Inner planets are Mercury, Venus,
Earth and Mars which are nearer to the Sun and separated from the rest of planets by asteroid
belt. These planets are smaller and denser than the more distant great planets. They are composed
mostly of rocks and have hard surfaces. They receive a substantial share of energy of the sun.
They have atmosphere consists chiefly of nitrogen and carbon dioxide. But the earth has a
significant amount of oxygen (20%) in its atmosphere.
The outer planets are Jupiter, Saturn, Uranus and Neptune. These lie beyond the asteroid belt and
are at great distance from the sun. These planets have low densities which are about the same
as water although Saturn could float on water. These planets are composed mostly of gases and
do not have solid surfaces. The atmosphere of these planets contain mostly of H2, He, CH4, and
NH3. They have long revolving periods. These planets receive a very small amount of the sun’s
energy so have low temperature.
The planets Jupiter, Saturn, Uranus and Neptune, which have diameters between 3.8 and 11.2
times that of the earth and masses, are called the giant planets. All having low densities are
probably composed largely of hydrogen. Their visible surfaces are thought to be clouds of
ammonia or methane. Jupiter, Saturn and Uranus have ring systems.
Despite the fundamental similarities they differ greatly in size, orbits, rotation period, revolution
period and other physical characteristics which is reflected in table given below.
Comparative Data of Solar System
Planets Distance Diameter Revolution Rotation Average Atmos- Mass No. of Density
from the (km) time Earth time surface phere compared Moon gm/cm3
sun (in day (d) or temp oC with the
106 km) Earth year O2, CO2, 01
H2O earth 0 0.97
Mercury 57.6 4880 (y) 59d -173 to taken as 1 11
243d 420 N2, O2,
Venus 108 12,104 88d 480 CO2, H2O 0.055
Earth 150 12,756 225d 24h 22 0.82
365.25d 1
Blooming Science Book 10 333
Mars 225.6 6720 687d 24h -50 to O2H, C2OO2, 0.107 2 0.73
12y 37m 40
Jupiter 768 140,800 29.5y
84y 9h 55m -143 H2, He, 318 62 0.25
Saturn 1600 113,600 164y CH4, NH3
Uranus 2870 51,200 10h -180 H2, He, 95.16 53 0.13
Neptune 4480 48,200 14m NH3, CH4
17h -210 CH4, H2, 14.54 27 0.23
14m He, NH3
16h -225 CH4 17.15 13 0.30
Source: For number of satellites IAU, WGPSN
Description of the Planets
1. Mercury (Budha): It is the nearest planet to the sun i.e. only 57.6 million km away from the
sun. Its two-third surface always faces the sun. It revolves around the sun once every 88 days.
However, it rotates slowly on its axis, about once every 59 earth days. This combination of
fast revolution and slow rotation makes a day on the mercury to last for 170 earth days.
During day, the surface temperature is about 420oC and at night, it drops to -173oC. This is
the largest temperature change on any planet in the solar system. Because Mercury does not
have an atmosphere, heat is not conducted from the hot sunlight surface to these so called
“cold traps”. The surface of Mercury is very similar to our moon with many craters. It has
no satellite. It shows phases like that of the moon.
2. Venus (Shukra): Sometimes called the “Earth’s twin”, the planet Venus is similar in
mass and size to the earth. So it is the earth’s closest planet. It is brighter than any other
planets or stars seen in the sky at night. So it is called brightest planet. It has a thick
cloudy atmosphere and its surface temperature is about 400oC. The atmosphere is mostly
made of carbon dioxide. Dense yellow clouds of sulphuric acid cover it. It completes one
revolution around the sun in 224 earth days. It is only a planet which revolve in clockwise
directions. It is the planet with the longest day: a day on Venus is 243 earth days. It has
no satellite. It shows phase like that of the moon. It can be seen in the western sky in the
evening after sunset and in the eastern sky in the morning before sunrise. So, it is called
as morning and evening star.
3. Earth (Prithvi): It is the third planet from the sun and is the largest of the four inner planets.
The average temperature of the earth’s surface is about 15 to 20oC. It is the only planet having
life on it. The conditions that makes life possible on the earth are; presence of plenty of
water in the liquid forms, sufficient oxygen in the atmosphere, and moderate temperature i.e.
neither too hot nor too cold. Other planets of the solar system do not have these conditions.
Thus, life is not possible on them. The earth has only one satellite.
Conditions required for supporting life on the planets:
a) Planets should have sufficient oxygen in the atmosphere.
b) Should have water in liquid form.
c) Temperature should be neither too high nor too low.
d) Should have a protective layer (like ozone) around.
334 Blooming Science Book 10
The earth rotates on its axis. It spines completely around every 23 hours, 50 minutes, and
4.03 seconds. The rotation makes the sun to appear to move from east to west. The earth
revolves around the sun in 365 days, 6 hours and 9 minutes and 9.54 seconds. As the earth
moves around the sun, the night sky changes slowly. Some groups of stars are visible in
the night sky and other groups disappear.
4. Mars (Mangal): It is the fourth planet from the sun. It is the only planet whose surface
can be seen in detail from the earth with the help of telescope. It glows with a reddish
light in the night sky. It has two satellites: Diemos and Phobos. It takes 687 days or 1.88
earth years to revolve once around the sun. Its diameter is about 6,744 km. It is aout 266.4
million km away from the sun. Mars is like the earth in some ways. Its day is about the
same length as the earth’s day. It has summer and winter seasons. Its temperature during
the day times is similar to that of the earth’s temperature but the night is low. It has thin
atmosphere, so cannot form the protective layer to check the entry of harmful radiation on
it. It contains more carbon dioxide and less oxygen. The space craft that landed on Mars
in 1976A.D found no sign of life. But the features that resemble dry rivers beds on the
surface led to believe that large quantities of water once flowed on its surface. The water
may be there in frozen state in the planet’s polar caps or beneath the crust of this planet.
Polar caps seem to change in shape with the change in seasons at present. Nix olympia is
an extinct volcanic mountain in Mars which height is 3 times of Mount Everest.
The rocks on the surface of Mars contain limonite, a compound of iron due to which it
looks red and hence called red planet.
5. Jupiter (Brihaspati): It is the largest planet in the solar system. It has the strongest
gravitational attraction at its surface. It has a diameter of 140,800 km. In terms of order,
Jupiter is the fifth planet from the sun. It revolves round the sun in 12 earth years. It spins
faster than any other planets. It is the planet with the shortest day: a day on Jupiter is 9
hours 55 minutes. This rapid rotation cause the planets to bulge at its equator and flattened
at its poles. It is always surrounded by dense clouds, so its surface is not clearly seen. It
is believed that the clouds are formed of frozen methane and ammonia. A red spot can be
seen on its clouds. Which is formed due to hurricane in the atmosphere of Jupiter. It is
about 40,000 km long and 32,000 km wide.
Jupiter has 62 satellites, four of them being very large while the other very small. These
four large satellites are Europa, IO, Callisto and Ganymede (largest satellite in solar system).
Its escape velocity is 61 km/sec.
6. Saturn (Sani): It is the second largest planet after Jupiter. It
has a set of seven thin rings around it and are separated by dark
gaps. The rings consists of many individual pieces of mixture
of ice and dust, ranging in size from a few centimeters to a few
meters across. It is at the distance of 1600 million km away
from the sun. It takes 29.5 earth years to revolve round the sun
and completes a rotation once every 10 hours and 14 minutes.
Its diameter is 1,13,600 km. Its surface temperature is -180ºC. It has the lowest density of
all the planets, only seven tenths (0.7 gm/cm3) that of water. It can float on water. It has
more number of satellites about 53. Titan is its largest satellite. It is the only satellite in the
solar system with a thick atmosphere. Its atmosphere consists mostly of nitrogen.
Blooming Science Book 10 335
7. Uranus (Arun): It was the first planet to be discovered with the help of a telescope. It is the
seventh planet from the sun. It has its axis tilted at an angle of 98º from the perpendicular
position so that it is almost in level with its orbit around the sun. It is at the distance of
about 2870 million km from the sun. Its diameter is 51,200 km. It takes 84 years to revolve
once round the sun and 10 hours and 49 minutes to rotate once in its axis. Its atmosphere
consists of methane and hydrogen. Its surface temperature is -210ºC. It has 27 satellites.
8. Neputne (Varun): It is at the distance of about 4480 million km from the sun. Its diameter
is 48,000 km. It takes 165 years to revolve around the sun and 15 hours and 48 minutes
to rotate in its axis. Its atmosphere consists of hydrogen and methane. It is the only planet
in the solar system that travels east to west. It has 13 satellites and Triton is the biggest
among them. Its surface temperature is - 220ºC.
Activity-1
Draw a labelled diagram of solar system in a chart paper and keep it in your classroom.
Smaller Solar System Bodies
Asteroids: Asteroids (Greek asteroids: star-like, which is how they appear in a telescope) are
more properly called planetoids or minor planets, because, like planets, they move in orbits
around the sun in the asteroid belt between the paths of Mars and Jupiter. Asteroids are relatively
small planetary bodies in the wide gap between the orbit of Mars and Jupiter, that revolve around
the sun in their respective orbits. They do not have fixed shape. Also they have unusual orbits to
circle around the sun. Juno, vesta, eras, pallas, etc. are some examples of asteroids. Now ceres is
consider as dwarf planet so pallas is the largest asteroid.
Mars Mercury Jupiter Saturn
Sun Venus Neptune
Earth
Uranus
Solar system showing asteroid belt
Comets (Tailed star)
A comet (Greek; kometers; long haired) is a collection of gases, dust and ice which appear as a
bright ball of light in the sky with a long glowing tail. They are believed to be formed from left
over particles of the gas cloud that formed the solar system. Like the planets, they revolve around
the sun in elliptical orbits. But the orbits of most comets are tremendously elongated, with one
end near the sun and the far reaches of space at the other. For example, Halley’s comet appears
336 Blooming Science Book 10
within 87 million kms of the sun, then races away.
A comet is a frozen chunk of gas, dust and ice, which when approaches the sun, it begins to
resemble a fuzzy star with long shiny tail.
Orbit of the Comet
Nucleus
Earth Sun
Coma
Comet Orbit of the earth
A typical comet consists of three main parts; the nucleus, the coma and the tail. The nucleus (or
head) consists of crumbly rock particles trapped inside a frozen liquid. When the comet is some
distance away from the sun, it appears only as the nucleus. But as it approaches near the sun, its
outer icy part melts and boils away into vapour. Along with the dust particles, the evaporating
layers form a hazy cloud called the coma around the nucleus. The nucleus and coma together
form the head of the comet. The solar radiation sweeps away some of its gases and dust into a
long glowing tail that may be as much as 800 million kms long pointing away from the sun.
Therefore, as the comet approaches the sun, its tail follows the head. As the comet travels from
the sun, its tail leads and the head follow (Its tail gets shorter). When the comet moves far away
from the sun, it cools and returns to the frozen condition.
A comet is a non-luminous body, which appears bright by reflecting the light of sun. Sometimes
comet does not return back because they may collide with heavenly body and finish up (eg. shoe
make Levi) or completely evaporates when approaching to sun.
Edmund Halley: 1656-1742AD was the English Scientist. He became
famous for his research on comets. He proved that the comets seen in
1531, 1607 and in 1628AD were the same comet. He predicted that it will
be seen in 1759AD again and it happened so. So, it was named Comet
Halley. This comet has been seen in 1835, 1910 and 1986AD.
The period of revolution of comets round the sun is variable. For
example, Halley’s comet has a period of about 76 years. It has been
seen in 1986AD. Comets like the Shoemaker-Levy appeared in 1992
but crashed on Jupiter in 1994. Shoemaker-Levy was named after its
discovery Carolyn Shoemaker and David Levy. Table given below shows
some famous comets.
Some Famous Comets
Name First observed Revolution period (Earth years)
Halley’s comet 240 B.C. 76
Temple-Tuttle 1366 33
Blooming Science Book 10 337
Enke 1786 3.33
Schwasman Washman 1927 15
Bennett 1969 15
Shoemaker Levy 1993AD Collided in 1994 with Jupiter
Hyakutake comet 1996 20000
Each time the comets come near to the sun, they lose some of their ice, dust and gases and end
up as Asteroids. Some of these particles come within the gravitational field of the earth and burn
and destroyed completely in atmosphere.
Meteors and Meteorites
Meteors (Falling or Shooting Star)
A meteor is a bright streak of light seen for a short duration of time in the sky on a clear night.
So, it is also called shooting star or falling star because it looks like a star falling from one
direction to the other in the sky. Very big and bright meteor is also called fire ball. A meteor is
indeed small piece of solid matter consisting of stones and metal like iron and nickel that enters
the earth’s atmosphere from space. When these bodies are in space, they are called meteoroids.
As they enter the atmosphere at high speeds, air resistance cause them to heat up and emit light.
Most of them break up and burn completely in air before reaching the earth’s surface that is,
they disappear in atmosphere which is called meteor. It is believed that about 200 million visible
meteors enter the earth’s atmosphere every day.
Meteorite
The unburnt masses of the meteors that reach the Fig: Crater formed by meteorite
earth’s surface are called meteorites. So meteorite (in Arizona, USA)
is an extra terrestrial object from the space, which
reaches the Earth’s surface without being completely
burned up. It is a mass of metallic or stony material
or both. Meteorites range from dust to 60 tones.
Meteorites are of three types: (i) Stony meteorites, (ii)
Iron meteorites, and (iii) Stony iron meteorites.
1. Stony meteorites - These meteorites contain
more silica and less iron and magnesium.
2. Iron Meteorites - These meteorites contain more iron and negligible amount of silica.
Most of the meteorites that fall on the earth are of this type.
3. Stony iron meteorites - These meteorites contain both the silicon and iron in equal amount.
The big meteorites often form craters on the surface of the earth where they have fallen. There are
several craters on the earth that were caused by meteorites. One of the largest crater is in Arizona
desert in the USA. It is known as Barringer Crater. It spans about 1,275 meters in diameter and 175
meters deep. The largest meteorite known is the 54 metric tons. Hoba meterorite which fall on the
earth in 1920AD in Namibia.
Meteorites have been found on the moon and Mars also.
338 Blooming Science Book 10
Differences between a Star and a Shooting Star
S.N Star S.N Shooting Star (Meteor)
1. It is made up of gases like hydrogen. 1. It is made up of rock and metals.
2. It has light of its own (luminous). 2. It does not have light of its own.
3. It does not burn due to friction. The 3. It burns due to friction with
energy is produced due to nuclear fusion. atmosphere.
4. It is very big. 4. It is very small.
Differences between a meteor and a meteorite
Meteors Meteorites
1. They burn in earth’s atmosphere and 1. They burn in earth’s atmosphere but
finish. reach to the earth’s surface.
2. They are small. 2. They are big.
Satellites
A satellite‑ is a solid heavenly body that revolves around a planet.
The Mercury and Venus have no satellite. The six planets of the solar
system have a total of 173 known satellites. The satellites have no
light of their own. They shine because they reflect the light of the sun.
Earth has one satellite. The satellite of the earth is called the moon.
Moon is the natural satellite of the earth. It is about 384,400 km away
from the earth. Lots of findings about the moon have been done. In July 20, 1969A.D, two American
astronauts Neil Armstrong and Edwin Aldrin landed on the moon while Michael Collins circled the
moon in the ‘Mother rocket’. The former USSR launched unmanned rocket ‘Luna’ in 1959A.D.
Luna I went close to the moon. Luna II landed on the moon. Luna III orbited the moon and took
photographs of the rear, far side of the moon, the side that is never seen from the earth. The moon
revolves round the earth. The moon completes its one resolution around the earth is 27.23 days
which is called as sidereal month. The time taken to form two consecutive new moons or full
moon is called synodic month. It is 29.5 days. The satellites of each planet is given below in the
table.
Satellites in the Solar System
S.N Planets No. of Satellites Name of the Satellites
1. Mercury - -
2. Venus - -
3. Earth 1 Moon
4. Mars 2 Phobos and Deimos
5. Jupiter 62 Europa, IO, Callisto, Ganymede
6. Saturn 53 Titan, Dione, Tethys, Mimas, Encenadus
7. Uranus 27 Miranda, Ariel, Umbrial, Titania, Oberon
8. Neptune 13 Triton, Nereid
Total 158
Blooming Science Book 10 339
Artificial Satellite and Their Uses: The man made objects placed in orbits in outer space are called
artificial satellites. The satellites which keep revolving around the earth is called artificial earth
satellites or rockets. These comes to occupy a special orbit around the earth. It is a geo-stationary
orbit. The satellite is placed 3600 kms from the earth and orbits the earth in one day, period for the
own rotation round. So they appear stationary in the sky. The power needed for satellite to work
comes from solar cells that convert sunlight into electricity. This means that a satellite is always
above the same place on the earth.
Artificial satellites have many uses, such as:
1. Satellites are used for communication purposes like telephone, radio, television,
communication satellites receive radio signals and bring them down to another satellite
on the earth, making world-wise T.V., telephone, E-mail, Internet etc. services possible.
2. Weather satellites send picture of the earth’s weather, making weather forecasting easy
and accurate. Earth satellites are used for collection of data on the conditions in outer
space and observe heavenly bodies in space.
3. Remote sensing satellites can be used for detecting coal, oil and ores, ground water and
forest surveys.
4. To establish space research laboratory on the moon.
5. To establish sky labs to explore other planets in the space.
6. It is used for the collection of more information about other planets and outer space.
A natural satellite like moon cannot be used for communication purposes. It is because
a) It is far from the earth for receiving the signals.
b) Its period of revolution around the earth is not same as that of the period of rotation
of earth around its axis.
Galaxies
There are uncountable stars scattered in the space. These stars occur in clusters and each cluster
contains billions of stars. The spaces between the stars are filled by gas and dust particles. Thus,
galaxy is a giant assemble of billions of stars, interstellar gas and dust particles forming their
own cluster in the universe all held together by gravity. Typical galaxies contains ten million to
one trillion (107 to 1012) stars. Most galaxies are several thousand to several hundred thousand
light years in diameter and are usually separated from one another by distance on the order of
millions of light years. All these stars revolve around a common centre of galaxy. The period
of revolution around the center may extend up to hundreds of millions of years. Galaxies come
in many shapes and sizes ranging from dwarf galaxies of a few hundred millions stars to giant
galaxies of hundreds of billions of stars. There are more than hundred billions of galaxies in the
universe. The average number of stars in a galaxy is 1010.
Galaxies vary enormously in size. Some galaxies may have diameters of about 5,000 light years.
Giant galaxies can have diameters of 1,000,000 light years.
Galaxies are classified on the basis of their shape. Individual galaxies come into three main
types: Elliptical, Spiral and Irregular.
1. Elliptical Galaxies: These galaxies range in shape from round to flatten. They have a central
340 Blooming Science Book 10
bulge. Stars are arranged in the form of an ellipsoid around the bulge. The luminosity of the
galaxy is the highest at the center bulge and decreases outwards. It consists of very old stars.
These galaxies are numerous. Eg. Maffei I, M 59, M 49, M 87, M 89, etc.
2. Spiral Galaxies: These galaxies are highly active and are brighter than other galaxies.
About 70% of the galaxies are spiral. They consist of a bright core in the center with spiral
arms radiating from it. The arms rotate around this bulge. These galaxies are rich in gases
and dust. They give off many kinds of radiations such as gamma rays, X-rays, UV rays,
radio waves, visible light etc. Stars are being formed in these galaxies at a furious pace
from the hot gases and dust that they contain. Andromeda and the Milky Way are the spiral
galaxies. Andromeda is seen in the northern hemisphere.
Overhead view Side view
(Note: The sun’s size is very exaggerated. In reality the sun would be just a tiny speck!)
The Milky Way is the name of the galaxy in which Milky way
our earth, with all the other members of the solar
system are located. In other word it is our home
galaxy (also known as galaxy, with capital G). It
was first studied extensively by Harlow Saphley in
1917AD. It is a galaxy of about 100,000 millions
or more stars and huge clouds of gases as well as
dust. Each of these clouds along with the stars in it
is called a nebula. Because of the dust and the gases,
the light of the stars appears to be faint.
All the members of Milky Way galaxy are revolving around its galactic center. The sun
revolves around the galactic centre at a speed of about 250 km/s. Even at this tremendous
speed, it takes about 200-250 million years to make one complete revolution around its
galactic centre. The time taken by the sun to revolve once around its galactic center is
called one cosmic year.
3. Irregular Galaxies: Galaxies which cannot be classified as elliptical or spiral type
are called irregular galaxies. Their shape cannot be fitted into any shape pattern. Such
irregular galaxies constitute only 10%. These galaxies do not rotate about a central core.
Great Mazarin is an irregular galaxy. It is less brighter than spiral galaxy.
Generally these galaxies do not occur in isolation. Our own galaxy exists is a cluster of
about 20 galaxies known as the local group. Andromeda is the sister companion of the
Milky Way in this local group.
Blooming Science Book 10 341
Constellations
A constellation is any one of the 88 areas into which the sky or the celestial sphere is divided
along with all stars in it. The term constellation is also used to denote a group of stars visibly
related to each other in a particular pattern or configuration. These patterns resemble some known
objects and animals figures.
The patterns of the constellations are fixed throughout the year. But due to the revolution of the
earth around the sun, some constellations are seen only during certain seasons. Pleides and Orion
are seen during winter. Similarly different constellations can be seen from northern and southern
hemispheres at the same time.
The ancient people named the constellations observed in the Northern Hemisphere after the
names of the Greek heroes, gods, animals and the objects, which they seemed to resemble. Ursa
Major (Great bear) or Saptarishi, Ursa Minor, Orion (the hunter), Leo, Pisces, Andromeda,
Cassiopeia, Perseus etc. are some of the common constellations named according to fairy tail.
Between 1400’s and 1700’s, navigators exploring the Southern Hemisphere observed many
constellations and named them after the scientific instruments, animals, etc. For example,
Telescopium named after scientific instrument, telescope, Musca named after housefly.
The modern definition of constellation is, however, different. Astronomers have divided the
sky into different regions called constellations and named 88 constellations. The names of the
constellations have been derived from the groups of bright star contained in them. For example,
the region of the sky which contains the group Ursa major is now called the Ursa major (containing
the Big Dipper). Thus, a constellation is a particular region of the night sky which includes a
prominent group of stars.
Ursa Major: It is also known as the Great bear. It is a group of seven stars and resembles pan
with handle, so called dipper. This ways called the great bear because, it resembles bear along
with some less bright stars in the vicinity. This constellation is clearly visible in the northern sky
during summer (April to June).
Polaris
Ursa Minor
(a) Ursa Major or Great Bear (b) Orion or Hunter
342 Blooming Science Book 10
Ursa minor: It is also know as little bear. It is a group of 7 stars. Out of seven stars, four stars
form the bowl of the little dipper and three stars form the handle of the dipper. This constellation
can be seen in northern hemisphere during rainy season (June to August). The stars are closer
here then Ursa Major, at the end polaris can be seen.
Orion: It is also a group of seven stars seen in the southern sky. It is visible from most places on
the earth at one time or another during the year. It contains a well-known star pattern that has the
form of a hunter. It is seen during winter.
Lion: It is a group of bright stars outlining the form of a lion.
Constellations used in Astrology are called as the sign of zodiacs which are 12 in number. They
are:
1. Aries (Ram) 2. Taurus (Bull) 3. Gemini (Twins) 4. Cancer (Crab)
5. Leo (Lion) 6. Virgo (Virgin) 7. Libra (Scales) 8. Scorpio (Scorpion)
9. Sagittarius (Archer) 10. Capricorn (Goat) 11. Aquarius (Water-carrier) 12. Pisces (Fishes)
Myths related to zodiacs:
The following are the myths related to zodiac.
1. The constellations form patterns clearly resembling people animals or object.
2. Constellation is used to predict the future which does not have scientific proof.
3. Bad and good future cannot be forecasted by using zodiac sign.
4. Using the rings according to the zodiac sign has no scientific evidences.
5. People compare the characters of a person with the zodiac sign’s characters, which is
wrong.
There are some aspects of Astrology that can't be contested. The reality is, Astrology is both
antiquated and modern; another reality is that Astrology is a language of symbols.
When we work in the realm of Astrology, we utilize an orderly, detailed, insightful and illustrative
terminology.
Astrology speak isn't capricious, it isn't whimsical it pertains to the universe, mythological
legends, the Solar system, numerical interconnection uniting the celestial body, to aspects of our
natures, our individual lives, and historic events.
The Race to the Finish
There are many varieties of this story. Some say that the Jade Emperor called a race of animals
on his birthday to create the Chinese zodiac. Others say that it was in fact, the Buddha who did.
Nevertheless, both stories are essentially the same, excluding some minor details.
According to myths, the twelve animals of the Chinese zodiac were selected through a race. This
race is meant to create a time measurement for the people. There could only be twelve winners
and in order to win, the animals had to cross a rapid current river and reach the finish line on the
shore.
Originally, there was a cat and a rat, who hated each other with a passion. It’s hard to believe that
they were once friends. These two were the worst swimmers in the animal kingdom, but they
Blooming Science Book 10 343
were both smart. They discovered that the fastest way to the river is to hop on top of the ox. The
generous ox agreed to carry them across the river. However, the rat was so eager to win that he
pushed the cat into the water; thus the cat never forgave the rat, and wasn't included in the race.
Other variations of the story say that the rat just never told the cat about the race and did not even
compete at all.
Afterwards the ox and the rat made it to shore. The rat jumped in front of the ox and came first
in the race. The ox came in second and the tiger finished in third.
Importance of study of constellations
1. People use the constellations to estimate the time at night.
2. Some constellations are seen only during certain seasons. So they help us to know the
seasons.
3. Navigators use the patterns of the constellations to locate their positions and to find the
trial they want to go.
The following table presents differences between the galaxy and the constellation:
Galaxy Constellation
1. A galaxy is a collection of a large number 1. A constellation is a collection of some
of stars. number of stars staying in a pattern.
2. A galaxy does not have a known pattern. 2. A constellation has a known pattern.
3. There are about 1011 galaxies in the universe. 3. There are only 88 constellations known so
far.
Let's Learn
1. Pluto is not considered as a planet because it crosses inside the orbit of Neptune and
remains their for a long period. So, it is called dwarf planet.
2. Asteroids are called minor planets because they revolve around the sun in the same way
the planets revolve. Most of the asteroids are found in between the orbits of the planets
and they are smaller than major planets. Thus, they are called minor planets.
Points to Remember
1. There are numerous galaxies in the universe. There are about 106 to 1013 stars in each
galaxy.
2. One light year is equal to 9.46 × 1012 km.
3. The solar system is in Milky Way galaxy. There are about 1010 stars in this galaxy. There
are 1011 galaxies.
4. A constellation is a collection of few stars staying in a pattern. There are only 88
constellations known so far.
5. Sun is a medium sized star. It revolves around its galactic centre.
6. Solar system consists of eight planets, satellites, dwarf planets, asteroids, meteorites,
comets and interplanetary dust.
7. Pluto is a dwarf planet. Ceres in the asteroid belt is also a dwarf planet.
344 Blooming Science Book 10
8. The planets do not twinkle. They shine due to reflected light of the sun.
9. The period of one revolution of a planet orbit is its year.
10. A day is the length of time that is taken by a planet to rotate on its axis. A day on earth
takes 24 hours.
11. A day on Venus is longer than its year; a day on Venus takes 243 earth day and a year takes
only 224.7 earth day.
12. A day on Jupiter is only 9.8 earth hours.
13. The largest planet is Jupiter. It is followed by Saturn, Uranus, Neptune, Earth, Venus,
Mars and Mercury.
14. The outer, gaseous planets are much less dense than the inner, rocky planets. The earth is the
densest planet. Saturn is the least dense planet; it would float on water.
15. Most planets, including the Earth, rotate as they revolve, in a counter-clockwise direction.
Venus, alone among the planets, rotates clockwise. If it were possible to see the sun from the
surface of Venus, it would rise in the west and set in the east.
16. The planets closest to the sun move around their orbits faster than those farther away.
17. A belt of asteroids (minor planets made of rock and metals) lies between Mars and Jupiter.
18. Meteor is a burning object that resembles a falling star.
19. Meteorites are of three types; stony, iron and stony iron.
20. As a comet approaches the sun, tail is formed due to solar heat and wind.
Project Work
Organize some observation programmes at night with clear sky. You can observe the
craters of the moon, venus or any other planet if an astronomical telescope is available. If
telescope is not available you can identify and observe the constellation like ' Sapta Rishi'
(ursha major) in the northern sky with the help of your teacher or elders of your family.
Exercise
1. Define light year. Show by calculation. 1 light year = 9.46 × 1012 km
2. The distance between the sun and the earth is 8 minutes 20 seconds. Convert this distance
into meter. (Speed of light = 3 × 108 m/s) (Ans: 15 × 108 m)
3. Which unit is used for measuring the distance within the solar system? Define it.
4. What is a galaxy? In which galaxy does the solar system lie? What is the shape of that galaxy?
5. How far is the sun from the galactic center of the Milky Way?
6. How many planets does our solar system have? Name any four different heavenly bodies,
other than planets, that are found in our solar system.
7. Classify galaxy. What is the average number of stars in each galaxy?
8. A comet is not actually a star. Give two evidences in favour of this statement.
9. What are comets? Name the comet that is seen at regular intervals of 76 years? When was
it last seen?
10. Why does a comet develop a tail when it comes nearer to the sun?
11. What is a constellation? How many constellations are there? Name two constellations.
Blooming Science Book 10 345
Write two advantages of studying about constellations. Mention some myths related to
zodiac sign.
12. Why are meteors called shooting stars? How does a shooting star differ from a star? Is it
a real star?
13. Distinguish between:
a. Meteors and Meteorites b. Galaxy and constellation
c. Outer planets and inner planets d. Shooting star and star
e. Asteroids and planets f. Light year and astronomical unit
g. Stars and planets h. Comet and meteor
14. How far is the nearest star from the earth? (Express your answer in light year)
15. What can be estimated about the mean surface temperature of the planets as their distance
increase from the sun?
16. Why do some stars look much brighter in a clear sky at night?
17. Mention the following:
a. Planet nearest to the sun.
b. The planet which has maximum number of satellites.
c. The largest planet of the solar system.
d. The planet having a unique system of ring.
e. Two planets, which are nearly, twin in size.
f. The planet without a satellite.
18. Can Mars support life? Justify your answer with two evidences.
19. Why does the sun appear to move from east to west?
20. What are artificial satellites? Mention any three reasons of lunching artificial satellites into
the space.
21. Give reason:
a. The surface temperature of the Mercury reaches very high (about 420oC) at day and
very cold at night (–170°C).
b. The meteors disappear in the atmosphere.
c. Life is not possible on Mercury.
d. The tail of a comet seems longer when it is nearer to the sun and it seems shorter
when it goes far away.
e. Meteors cannot be observed from the moon surface.
f. The sun is a star but the Earth is a planet.
g. Tail of comet does not always remain in the existence.
346 Blooming Science Book 10
h. Mars is red in colour.
(Hint: Due to presence of red coloured mineral limonite)
i. Water, oxygen, carbon dioxide are present on Venus, even there life is not possible.
(Hint: Due to presence of very high temperature i.e., 460oC).
j. Some planets look brighter than stars.
(Hint: Planets are close to the sun and reflect more light. Stars are far away and less
light comes to the earth)
k. Comet is seen at a gap of long period of time.
22. Answer the following questions on the basis of the data given in the table below.
Name of the planet Revolving time about is orbit Temperature
A 87.97 earth days -173oC to 420oC
B 365.25 earth days 22oC
C 84 earth year -210oC
a. Which planet lies farthest from the sun?
b. Why is there vast difference in maximum and minimum temperature in planet A?
c. What is the reason for the lowest temperature at planet C?
d. In which planet is there possibility of life?
23. Study the table given below and identify A, B, C, D, E and F.
A The planet is red in colour and has two white polar cape.
B Although it does not have light of its own, but it is the brightest object in the sky.
C An ice ball that orbits the sun and looks like a broom when approaches the sun.
D Third planet from the sun with the average temperature of 15°C to 20°C.
E Largest satellite in the solar system with a thick atmosphere.
F A group of objects of the solar system that have failed to assemble into a planet.
24. Write short notes on:
a. The Milky Way b. Galactic centre
25. Show the differences between: c. Light year and cosmic year
a. Star and constellation
b. Comet and asteroid
26. Identity the star, planet, satellite, asteroid, comet, galaxy, dwarf planet and constellation
from the following:
i. Milky Way ii. Big dipper iii. Proxima Centaury
iv. Enke V. Ceres vi. Cassiopeia
vii. Vesta viii. Halley ix. Pluto
x. Sun xi. Phobos xii. Jupiter
xiii. Ganymede xiv. Andormeda
Blooming Science Book 10 347
27. Choose the correct alternatives from the following options.
i. The brightest planet in the solar system is:
a. Earth b. Mercury
c. Venus d. Mars
ii. Which one is called as shooting star?
a. Comet b. Meteor
c. Meteorite d. All of them
iii. The heavenly bodies lie in between mars and Jupiter is:
a. Asteroids b. Comet
c. Meteorites d. None of them
iv. Which comet is seen in interval of 76 years?
a. Temple-Tutle b. Bennett
c. Enke d. Halley’s
v. The constellation seen during rainy season is:
a. Ursa Major b. Ursa Minor
c. Orion d. None of them
Activity for Practice
1. During the clear sky at night, observe the sky (use telescope if you have).
a. Among the planets, Venus, Jupiter and Mars will be easy to distinguish. Find out at
what time these planets are visible.
b. Milky Way galaxy can be seen during November/December. Find out it.
c. Meteor shower: you can see in the sky near the north pole a falling star or a meteor
shower. It is necessary to watch for some time. Sometimes, 2-4 meteors shower
may be seen in same time.
2. Make large chart of the solar family. Apply colours to the planets that match them. Also
show the satellites. Attach a brief statistics about the planets below the chart.
348 Blooming Science Book 10
Class X Examination Specification Grid - 2074
Compulsory Science (Theory)
Time: 2.15 hrs.
Full Marks: 75
Pass Marks: 30
Area Chapter K U A HA Remarks
Physics 5×1=5 4×2=8 2×3=6 1×4=4 23 mark
1. Force
Chemistry 2. Pressure 4×1=4 4×2=8 2×3=6 1×4=4 22 mark
3. Energy
Biology 4. Heat 5×1=5 4×2=8 2×3=6 1×4=4 23 mark
Astronomy 5. Light
6. Electricity and Magnetism 1×1=1 1×2=2 × 1×4=4 7
and 15 13 6 4 38
Geology 7. Classification of Elements 15 26 18 16 75
8. Chemical Reaction
9. Acid, Base and Salt
10. Some Gases
11. Metal
12. Carbon and its Compounds
13. Materials used in Daily Life
14. Invertebrates
15. Human Nervous and Glandular Systems
16. Blood Circulatory System in Human Body
17. Chromosomes and Sex Determination
18. Reproduction
19. Heredity and Genetics
20. Environmental Pollution and its Management
21. History of the Earth
22. Atmosphere and Climate Change
23. The Universe
Total questions
Total marks
Note: K=Knowledge type questions U=Understanding type question
A= Application type questions HA= Higher ability type questions
Specification Grid (Practical)
Time: 45 min.
Full Marks: 25
Pass Marks: 8
Area Spotting Practical record Material Mini project Viva/voce Total
construction work
Marks 5 6 4 25
Time allocation 15 min 6 4 5 min 1 hr 20 min
60 min 10 min
The students will be evaluated in theory and practical separately.
Blooming Science Book 10 349
Model Question
ljifo M lj1fg k0" ff{ª\s M &%
pTtL0ffª{ \s M #)
sIff M !) ;do M @ 306f !% ldg]6
15 × 1 = 15
Group 'A'
1. a. u'?Tjfsif0{ f cr/ cª\s (G) nfO{ kl/eflift ug'x{ f;] \ .
Define Universal Gravitation Constant 'G'.
b. kf:snsf] lgod nV] g'xf;] \ / o;df cfwfl/t sg' } bO' { pks/0fx¿sf] gfd pNn]v ug'x{ f;] \ .
State Pascal's law and name any two instruments based on it.
c. phf{sf] ;f| t] slt ks| f/sf xG' 5g\ < pbfx/0f ;lxt gfd nV] gx' f;] \ .
What are the various types of energy sources? Name them with an example.
d. cb/' b[li6 eg]sf] s] xf] <
What is short sightedness?
e. 1 ol' g6 ljb\ot' sf] kl/efiff lbg'xf];\ .
Define 1 unit electricity.
f. cfwl' gs k]l/ofl] 8s lgod n]Vg'xf;] \ .
State Modern Periodic law.
g. ;o+ f]hg kl| tljm| of sn] fO{ elgG5 <
What is meant by combination reaction?
h. c0f';q' ;lxt sg' } bO' { cf6] f Iff/x¿sf] gfd nV] g'xf];\ .
Name any two bases with molecular formula.
i. aS;fO6 wfpaf6 s'grflx wft' lgsfNg ;lsG5 <
Which Metal can be extracted from bauxite ore?
j. dfO6f]l;; sf]if ljefhg egs] f] xf] <
What is Mitosis cell division?
k. xdf{g] eg]sf] s] xf] <
What is hormone ?
l. ln+u lgwf{/0fsf] kl/efiff lbgx' f];\ .
Define sex determination.
m. dlN6kn lkmhgaf6 k|hgg\ ug]{ bO' { cf6] f hLjsf] gfd n]Vgx' f;] \ .
Name two organisms which are reproduced by the methods of multiple fission.
350 Blooming Science Book 10
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