Oasis School Science and Technology 8 New

Oasis School Science and Technology - 8 297 Activity 4 To demonstrate that temporary hardness can be removed by boiling water • Take a beaker and put some water into it. • Add one spoon of calcium bicarbonate or magnesium bicarbonate into the water and stir with a glass rod. • Now, add a few drops of shampoo or solution of soap into the beaker and observe whether lather is formed or not. • The water does not produce lather. It proves that the water is hard. • Now, boil the water in the beaker and allow it to cool. • Again, add a few drops of shampoo or solution of soap and stir with a glass rod. Observe whetherlatheris formed or not. The water produces lather with soap after boiling. It proves that temporary hardness of water can be removed by boiling. Alloy The homogeneous mixture of two or more metals or metals and non-metals is called alloy. The molten mass of two or more metals or non-metals when mixed completely, forms homogenous mixture. On cooling this mixture, we get a solid mass which is called alloy. The alloy which is formed by mixing a metal and mercury is called amalgam. The melting point of alloy is always lower than its component metals. But it has greater hardness and more brittleness. Properties of alloys i. Alloys are generally harder and stronger than their components. ii. They have metallic properties like malleability and ductility. iii. They are good conductors of heat and electricity. iv. They are more brittle than their components. v. They have generally low melting point than that of their components. Some alloys and their components S.N. Alloys Components 1. Brass Copper (70%) and Zinc (30%) 2. Bronze Copper (88%) and Tin (12%) 3. Bell metal Copper (80%) and Tin (20%) 4. Artificial gold (rolled gold) Copper (90%) and Aluminium (10%) 5. Stainless steel Iron (89.4%), Chromium (10%), Manganese (0.35%) and Carbon (0.25%) 6. Duralumin Copper, manganese and magnesium

298 Oasis School Science and Technology - 8 Brass Bronze Bell metal Rolled gold Steel Fig: Some examples of alloys Activity 5 • Take a few iron nails or a piece of iron. Keep it in a moist place and observe it after 3-4 days. What do you observe? You can see a reddish-brown layer on the surface of the iron nails. The formation of reddish-brown scales or powder on the surface of iron when it comes in contact with moist air is called rusting. As a result of rusting, weight of metal increases. To protect iron from rusting, we apply several methods like painting, forming alloys, galvanizing, etc. 4Fe + xH2 O + 3O2 2Fe2 O3 . xH2 O (Rust) Uses of brass Brass is an alloy of copper and zinc. It is used to make various objects because of its goldlike appearance, low melting point, durability and conductivity. Some of its uses are: i. It is mostly used to make musical instruments such as trumpet, gong bell and hand-bells. ii. It is used to make plates, cups, spoons and glasses. It's wise to use these because of their antimicrobial property. iii. It is used to make idols, flower vases, wands and ornaments. iv. Locks, gears, valves and bearings are usually made from brass because it is tensile. v. Brass is used for making decorative items such as statues, hourglass and watches. Fig: Some uses of brass

Oasis School Science and Technology - 8 299 Uses of bronze Bronze is an alloy of copper and tin. It is used to make various objects because it is wearresistance and hard. Some of its uses are: i. It is used in the construction of sculptures. ii. Some musical instruments, medals and bearings are made from bronze. iii. Bronze is used for clips, electrical connectors and springs. iv. In architecture, it is found in hardware, doors, entrances, fountains, handrails and column cladding. v. Modern safety tools such as hammers, mallets, and wrenches are also made of bronze. vi. Bronze is used for making statues and weapons. medals bronze sculptures bronze hammers electrical connectors Gong bell Fig: Uses of bronze Activity 6 What materials in our surroundings are made of brass and bronze? Make a list. Uses of steel Steel is an alloy of iron and carbon. Various forms of steel are found based on the addition of other elements. It is used in many ways. i. Steel is used for making cabinets and shelving units. ii. The cutlery and utensils we use every day are mainly manufactured from stainless steel. iii. Doors, engines, suspension and interiors of vehicles consist largely of steel. iv. Stainless steel is used to make bathroom accessories such as taps, bathroom hooks, toothbrush holders etc. v. Steel is used to make railing on the roof and ladders in houses. vi. Most surgical tools are made from stainless steel. Fact File An alloy is a mixture of multiple elements with at least one metal.

300 Oasis School Science and Technology - 8 Steel cabinets Steel utensils Steel surgical tools Fig: Uses of steel Reasonable Facts Brass is used for making decorative items. Brass is used for making decorative items because it has a beautiful gold-like colour. Reasonable Thinking Skill R T S 1. Soap scum is produced while washing clothes in winter in the hilly region. Soap scum is produced while washing clothes in winter in the hilly region because most water is hard water in the hilly region. Soap does not work properly in hard water. It forms scum. 2. Alloy is preferred to make utensils rather than the original metal. Alloy is preferred to make utensils rather than original metal because it has a low melting point than the original metal. It will be easy to mould them. 3. Utensils of brass are preferred to feed food to children. Utensils of brass are preferred to feed food to children because these tools are antibacterial. They kill bacteria. So, when kids eat food with brass utensils, they won’t be infected. 4. People are more attracted to use detergent than soap. People are more attracted to use detergent than soap because: i. Soap does not work in hard water but detergent does. ii. Detergents have more cleaning properties than soap. iii. Detergent is cheaper than soap. 5. What is the purpose of the permutit process? The purpose of the permutit process is to convert hard waterinto soft waterin laundries. It is usually used for washing clothes. 6. Differentiate between soft water and hard water. The differences between soft water and hard water are:

Oasis School Science and Technology - 8 301 SN Soft water SN Hard water 1 The soft water does not contain bicarbonates, chlorides or sulphides of calcium and magnesium. 1 The hard water contains bicarbonates, chlorides or sulphides of calcium and magnesium. 2 The soft water produces more lather and less soap scum. 2 The hard water produces less lather and more soap scum. 7. Differentiate between brass and steel. The differences between brass and steel are: SN Brass SN Steel 1 Brass is an alloy of copper and zinc. 1 Steel is an alloy of iron and carbon. 2 Brass is yellow. 2 Steel is silver or grey. 8. What is the importance of soft water? The software is very important because: i. It will not damage the metallic water pipes. ii. It is good for hair and skin. iii. It is easy to wash clothes in it. Exercises 1. Multiple choice questions a. Which of the following causes the temporary hardness of water? i. calcium carbonate ii. calcium sulphate iii. calcium bicarbonate iii. calcium chloride b. Which of the following causes permanent hardness of water? i. calcium carbonate ii. calcium sulphate iii. calcium bicarbonate iii. calcium oxide c. Which chemical substance is used in Clark’s method? i. sodium carbonate ii. sodium chloride iii. sodium zeolite iv. sodium bicarbonate d. In which process of converting hard water into soft water, sodium zeolite is used? i. clark’s method ii. boiling method iii. adding washing soda iv. permutit process e. What is the mixture of copper and tin? i. bronze ii. brass iii. steel iv. amalgam 2. Define the following terms with required examples. a. Soft water b. Hard water

302 Oasis School Science and Technology - 8 c. Temporary hard water d. Permanent hard water e. Alloy f. Amalgam g. Brass h. Bronze i. Steel 3. Very short questions a. What is present in hard water? b. What compound is known as a universal solvent? c. Name two salts that cause temporary hardness of the water. d. What chemical species is most used for converting hard water into soft for washing clothes? e. Write the molecular formula of sodium zeolite. f. What is the homogenous mixture of multiple metals called? g. What is used to make brass? 4. Give reasons. a. Water is called the universal solvent. b. Soft water is used to wash clothes. c. Soap does not work in hard water. d. Boiling water can remove temporary hardness. e. Adding lime water can remove temporary hardness. f. Detergent is added in permanent hard water. g. Permutit method is used in huge laundries. h. Alloys are preferred to make utensils than the original metals. i. Steel is used to making taps, utensils, sockets etc. 5. Differentiate between a. Soft water and hard water b. Temporary hard water and permanent hard water c. Clark’s method and permutit method d. Brass and bronze 6. Short questions a. How is the hardness of water removed by boiling? b. How is the hardness of water removed by Clark’s method? c. How does adding washing soda remove the hardness of water? d. How does adding sodium zeolite remove the hardness of water? e. Discuss the physical properties of the alloy. f. Make a list of a few salts that cause permanent hardness of the water. 7. Long questions a. Write any four physical properties of water. b. Mention the properties and uses of hard water. c. Mention the properties and uses of soft water. d. What is brass? Write down its uses. e. What is bronze? Mention the uses of bronze. f. What is steel? What are the uses of steel.

Oasis School Science and Technology - 8 303 11 EARTH AND SPACE UNIT

304 Oasis School Science and Technology - 8 UNIT 11.1 EARTH IN UNIVERSE AND MINERALS Estimated teaching periods Theory 4 Practical 2  Introduction to the universe  Big Bang Theory  Introduction to comet and asteroids  Introduction and examples of constellations, galaxy, meteors and meteorites  Introduction to minerals  Types of minerals (metallic and nonmetallic minerals)  Characteristics and uses of minerals  Important metallic minerals found in different locations of Nepal The Sequence of Curriculum Issued by CDC Georges Lemaitre is well known for the Big Bang theory. He was born in Belgium on 17th July 1894 and died on 20th June 1966. He was a cosmologist, astrophysicist and mathematician. He was the first to realize that the universe is expanding which was later confirmed by Edwin Hubble. He first derived Hubble’s law and Hubble constant which is now called Hubble-Lemaitre law. He proposed the Big Bang theory of the origin of the universe calling it the hypothesis of the primaeval atom. He was honoured with Francqui Prize and Eddington medal. He was educated at the Catholic University of Louvain, St Edmund’s House Cambridge and the Massachusetts Institute of Technology. About the Scientist Georges Lemaitre Key terms and terminologies 1. Universe : The universe is all of space-time and everything that exists therein including all planets, satellites, stars, galaxies, constellations, comets, dust particles, matter, energy, etc. 2. Astronomy : The branch of science in which we study about the universe is called astronomy. 3. Asteroids : The rock and metal objects which are present in between the orbits of Mars and Jupiter that revolve around the sun are called asteroids. 4. Asteroid belt : The region in-between Mars and Jupiter where millions of asteroids are found is called asteroid belt. 5. Planets : Those heavenly bodies which revolve around the sun are called planets. 6. Kupier belt : Kupier belt is a region that contains asteroids, dwarf planets,

Oasis School Science and Technology - 8 305 comets, etc. and lies behind the orbit of Neptune. 7. Trojans : Some celestial objects that revolve around the sun by intersecting the orbit of major planets are called Trojans. 8. Near-earth asteroids : The asteroids which are close to earth and intersect the earth's orbit are called near-earth asteroids. 9. Endocomets : The comets that are present and formed inside the solar system are called endocomets. 10. Exocomets : The comets that are formed outside the solar system are called exocomets. 11. Extinct comets : The comets that lose gas particles completely and leav the rocky core which start revolving around the sun as an asteroid are called extinct comets. 12. Zodiac : The 12 constellations that lie in the solar path are called zodiac constellations. 13. Comet : The huge chunk of ice that revolves around the sun is called a comet. 14. Coma : The clouds of evaporating ice around the head of the comet is called a coma. 15. Nucleus : The central part of the coma is called the nucleus of the comet. 16. Meteoroids : The falling bodies in space smaller than asteroids are called meteoroids. 17. Meteors : The pieces of stone or metal which enter the earth’s atmosphere are called meteors. 18. Meteorites : The meteors that hit the earth are called meteorites. 19. Meteor shower : Meteor shower is an event when multiple meteors fall from the sky at the same time. 20. Galaxy : A galaxy is a vast system of stars, dust particles and gases isolated from a similar system in space. 21. Spiral galaxies : Galaxies which are spiral in shape are called spiral galaxies. 22. Elliptical galaxies : The galaxies which are oval in shape are called elliptical galaxies. 23. Irregular galaxies : Galaxies that do not have a regular shape are called irregular galaxies. 24. Big bang theory : According to this theory, all the matter in the universe was originally concentrated in a lump called primeval atom. After its explosion, the universe is formed. 25. Constellation : The group of stars in the sky which has a fixed shape is called a constellation. 26. Minerals : Minerals are useful substances that are found in the crust of the earth. 27. Metallic minerals : The minerals that contain a significant amount of metals are called metallic minerals. 28. Non-metallic minerals : The minerals that do not contain a significant amount of metals are called non-metallic minerals. 29. Energy minerals : The minerals that can be used as fuel are called energy minerals.

306 Oasis School Science and Technology - 8 Introduction The universe is all of space-time and everything that exists therein including all planets, satellites, stars, galaxies, constellations, comets, dust particles, matter, energy, etc. In short, the vast surrounding space is called the universe. Universe is infinite. The part of universe that is visible to us through telescope is called observable universe. The sun is one of the stars among billions of stars in the universe. The earth on which we live is only a tiny speck of the universe. Billions of stars in the universe are not distributed uniformly. They occur in the form of clusters or group of stars called galaxies. Our solar system is located in the Milky Way galaxy. This galaxy consists of more than one billion stars. Among them, the sun is a medium sized star. The width of the universe is about 100,000 light years. The solar system is located about 30,000 light years away from the centre of the Milky Way galaxy. 1 Light year is the total distance travelled by a light in vacuum in a year. It's magnitude is 9.46 x 1015 m. Different studies about the universe were carried out with the help of powerful telescopes. The branch of science in which we study about the universe is called astronomy. To know about the universe, it is important to discuss the heavenly objects, like galaxies, stars, the sun, planets, satellites, comets, etc. Asteroids The rock and metal objects which are present in between the orbits of Mars and Jupiter that revolve around the sun are called asteroids or minor planets. There may be as many as 100000 asteroids in the solar system. Usually diameter of an asteroid ranges from 1 km to 1000 km. The region in-between Mars and Jupiter where millions of asteroids are found is called asteroid belt. The biggest asteroid is Ceres which has a diameter of about 940 km whereas the smallest asteroid is as small as a pebble. Examples of other asteroids are Juno, Vesta, Pallas, Eros (16.8 km Fact File Scientists estimate there are about 1022 stars in the universe. Fig. Universe Fact File In 1994 AD, Alexander Wolszcan discovered that there were three planets that revolve around a pulsar. fig: asteroids

Oasis School Science and Technology - 8 307 diameter), etc. Beyond the solar system, behind the orbits of Neptune, numerous rocks formed during the origin of solar system still exists. It also contains asteroids, comets and dwarf planets. This region is called Kupier belt. Some celestial objects revolve around the sun by intersecting the orbit of major planets. These are called Trojans. For example, Pluto. The asteroids which are close to earth and intersect the earth's orbit are called near-earth asteroids. They are threat to us. They can sometimes come toward the earth. Activity 1 Make a 3 D model of near-earth asteroids. Differences between Planets and Asteroids S.N. Planets S.N. Asteroids 1. Those heavenly bodies which revolve around the sun are called planets. 1. Those heavenly bodies which revolve around the sun mainly in between Mars and Jupiter are called asteroids. 2. They are bigger than asteroids. 2. They are smaller than planets. Comets When we observe the sky at night, we can see a tailed structure revolving around the sun. They revolve in a highly elliptical orbit where sun is never at the centre. A broom shaped shining object made of ice with a bright head is called a comet. The comets that are present and formed inside the solar system are called endocomet. The comets that are formed outside the solar system are called exocomet. Exocomet can also revolve around the sun nearyby Kupier belt. It is made of gases, dust and ice. The head is made up of ice. The clouds made of evaporating ice around the head of the comet is called coma and the central part of the coma is called the nucleus of the comet. Sometimes the normal path of the comet is disturbed by the star, and it starts moving towards the sun. As the comet approaches the sun, it develops a long glowing tail and becomes visible to us. A comet becomes visible only when it approaches the sun as the ice and gaseous particles get evaporated due to heating of the sun. The thus formed gas and particles of ice flow to the opposite direction of the sun due to the solar wind and form a long tail. So, comets are also called tailed stars. Actually a comet has two tails. They are dust tail and ion tail. Dust tail is made from dust. It is thicker and white. The ion tail is thinner and bright. It is formed from charged gas ions. The rays of the sun make its gas glow, which spread, out to form a tail millions of kilometres long. Comets have no light of their own. They reflect the light from the sun. Comets revolve around the sun in long elliptical orbits. Different comets have different Fact File Ceres is also classified as dwarf planet.

308 Oasis School Science and Technology - 8 periods of revolution. Some comets can complete revolution with in two years and some can take longer than 2.5 lakh years. Halley’s Comet is seen after every 76 years. It was last seen in 1986 AD. This comet was studied in detail by a scientist named Edmund Halley. So, it was named after his name. Sun Comet The comet's tail develops as it gets closer to the sun A comet spends most of its time in the outer solar system Fig. Comet revolving around the sun S.N. Name of Comets First Observed Revolution (years) 1 Halley’s Comet 240 BC 76 2 Temple- Tuttle 1366 AD 33 3 Enke 1786 AD 3.3 4 Schwasman- Washman 1927 AD 15 5 Bennet 1969 AD 1678 6 Shoemaker Levy 1992 AD unknown 7 Hyakutake 1996 AD 70,000 When the comets approach the sun, they lose some ice, gas and dust each time. Ultimately they convert into small fragments like asteroids. Some of the fragments enter the earth's atmosphere and with other heavenly bodies and get crumbled into pieces. As a result, some comets disappear forever. For example, Shoemaker levy comet can never be seen again because it collide with Jupiter in 1994. Some comets lose gas particles completely and leaves the rocky core. The rocky cores starts revolving around the sun as a asteroid. They are called extinct comet. It is believed that a comet with rocky core that hit the earth wiped out dinosaurs 65 million years ago from the earth during Cretaceous period of mesozoic era. Activity 2 Make a 3 D model of solar system and show comets and asteroids.

Oasis School Science and Technology - 8 309 Reasonable Facts The comet develops a tail when it comes nearer to the sun. When a comet approaches the sun, some of its frozen matter begins to evaporate into gases due to the heat of the sun. These gases rush out by rapid vaporization in the form of jets, carrying solid particles with them. In this way, a long tail of a comet is formed due to the motion of the comet and effect of the solar wind. Reasonable Facts A comet is seen only after a long period. Comets are seen in the sky when they approach the sun. Comets take many years to complete one revolution around the sun. For example: Halley's comet completes one revolution around the sun after 76 years. So a comet is seen only after a long period due to its very long elliptical orbit. Reasonable Facts A comet break into pieces on coming close to the planet Jupiter. When a comet comes close to the Jupiter, the parts of the comet that are nearer to the Jupiter experience much greater gravitational pull of the Jupiter than other parts of the comet. This large difference in the gravitational pull of the Jupiter, on different parts of the comet, breaks the comet into pieces. For example, in 1994, the comet called "Shoemaker Levy' broke into many pieces when it came too closer to Jupiter. Meteoroids Meteoroids are rocks that are smaller than the asteroids that float in solar system. They were probably formed during the formation of solar systems. They keep floating in space or inside solar system. Sometimes they enter the gravitational field of planets and change into meteors. Meteors (Falling stars or Shooting stars) The pieces of stone or metal which enter the earth’s atmosphere are called meteors. Almost 200 meteors fall toward earth each day. These are seen as streaks of light in the sky at night, which disappear within a few seconds. Some meteors are formed from the dust particles left behind by the comets, and others are pieces of asteroids which have collided. When the heavenly body enters the earth’s atmosphere with high speed, friction is developed between the body and air. Due to the friction, heat is produced in it, and a burning object is seen in the atmosphere in the form of a streak of light. A meteor lasts for a very short time because the small rock pieces burn and vaporize completely due to the excessive heat produced by atmospheric friction. Sometimes the big meteors do not burn completely Fact File Meteor shower is an event when multiple meteors fall from the sky at a same time.

310 Oasis School Science and Technology - 8 and may reach the surface of the earth. This object is called a meteorite. A large number of meteors fall near the North Pole and South Pole of the earth. A meteor shower can be seen in the polar regions. An extremely large and bright meteor is called fire ball. Depending on the composition of the material, the meteorites can be classified into the following three groups: i. Stony meteorites: They are meteorites having more amount of silicon than iron and magnesium. ii. Iron meteorites: They are meteorites having more amount of iron and negligible amount of silicon. iii. Stony iron meteorites: They are meteorites having almost equal amounts of silicon and iron. Reasonable Facts A meteor is finished before reaching the earth's surface. A burning stone resembling a falling star is called a meteor. When a meteor comes towards the earth's surface at a great speed, it burns completely due to the friction between the meteor and atmospheric gases. Therefore, a meteor is finished before reaching the earth's surface. About fifty thousand years ago, a meteorite fell in Arizona of USA, and a deep crater was formed, which is shown in the given figure. The crater was 1275 m wide and 175 m deep. This can be seen nowadays. Here, the main stone entered deep into the earth’s surface, but many broken pieces were scattered around the crater. It is, said that meteors start to burn at a height of 7km to 120 km. They have a speed of 70 km per second. The meteorites found on a earth are mostly iron type. The mass of meteorites found so far ranges from 100 grams to 20000 kilograms. Differences between Comets and Meteors S.N. Comets S.N. Meteors 1. Broom-shaped shining objects with a bright head made up of ice are called comets. 1. The pieces of stone or metal which enter the earth’s atmosphere are called meteors. 2. They have a long glowing tail-like structure. 2. They have streaks of light falling down towards the earth surface. Fig: meteor shower Fig. Crater in Arizona, USA Fig. Meteorite hoba

Oasis School Science and Technology - 8 311 Galaxy Space contains billions of stars. They have different clusters or groups. This cluster of billions of stars is called a galaxy. Thus, a galaxy is a vast system of stars, dust particles and gases isolated from a similar system in space. There are about 100 billion to 200 billion galaxies in observable universe based on the observation of New Horizons satellite. There are about 1011 galaxies in the universe. The diameter of a galaxy is about 1000 light years to 10 lakh light years. Types of Galaxies On the basis of shape, there are three types of galaxies. They are: a. Spiral galaxies: Galaxies which are spiral in shape are called spiral galaxies. Examples: Milky-way galaxy, Andromeda galaxy, etc. Our solar system is located in one corner of the Milky-way galaxy. This galaxy consists of 1011 stars. This galaxy has a disk-like structure at its middle which tapers towards its sides. It has a black hole has its nucleus surrounded by six arms. A dusty cloud is found between the stars of this galaxy. The mass of Milky-way galaxy is about 1.33 × 1011 times more than that of the sun. Activity 3 Visit planetarium with your guardian and explore milky way galaxy. b. Elliptical galaxies: The galaxies which are oval in shape are called elliptical-shaped galaxies. These galaxies contain a little amount of interstellar matter. The stars found in these galaxies are very old. Their peripheral part is dim and the central part emits bright light. c. Irregular galaxies: Galaxies that do not have a regular shape are called irregular galaxies. They have bright stars at the central part. These galaxies are less brighter than elliptical galaxies. The distance between the galaxies can be found with the help of electromagnetic radiation coming from them. Scientists say that the galaxies are moving apart at a very high speed. This signifies that space is expanding. Fig. Spiral galaxy (Milkway galaxy)

312 Oasis School Science and Technology - 8 Fig. Elliptical galaxy Fig. Irregular galaxy Activity 4 Make a 3D model of each type of galaxy. Big Bang Theory The theory of Big Bang is proposed by George Lemaitre in 1927. According to this theory, all the matter in the universe was originally concentrated in a lump called a primeval atom. About 13.8 billions years ago, this super dense and extremely hot body having neutrons and protons exploded with a big bang, and the matter started flying in all directions through space, leading to the formation of galaxies of the stars and other heavenly bodies. Now, we are nearly 13.8 billion years after the Big-Bang explosion, and it is believed that the universe is expanding continuously and will continue in the future as well. Edwin Powell Hubble's observation has confirmed through his red-shift experiment that the universe is expanding and accelerating. Constellation We have seen thousands of stars in a clear night sky. Some of them are in a group or pattern. The group of stars in the sky which resemble an animal or any other shape is called a constellation. Our ancestors named those stars or constellation after the object which they seemed to resemble. Till now 88 constellations are known. That means 88 groups of stars have got names. Each constellation has been given a name signifying an animal, a human being or some other objects to which it appears to resemble. Some of the famous constellations are: 1. Ursa Major 2. Ursa Minor 3. Aries 4. Orion 5. Taurus 6. Gemini 7. Cancer 8. Leo 9. Virgo Fig. Big Bang Explosion Fact File In 1970 Stephen Hawking supported the theory of creation of universe through the mathematical singularity, the big bang. He published this thing in his book 'a brief history of time: from the big bang to black holes' in 1988.

Oasis School Science and Technology - 8 313 10. Libra 11. Scorpio 12. Sagittarius 13. Capricorn 14. Pisces 15. Aquarius 16. Draco 17. Cepheus 18. Cassiopeia 19. Perseus 20. Hydra (biggest) 21. Crux (smallest) Cassiopeia Ursa Major Ursa Minor Cepheus Fig. Some constellations From 1400 AD to 1700 AD, sailors gave names of scientific material, animal, etc. to the constellations seen on their ways to the southern hemisphere, e.g., Tucana, Musca, Telescopian, etc. The constellations seen in a particular season are not visible in another season due to the revolution ofthe earth around the sun.We can see different constellations from the north and south hemisphere of the earth. The 12 constellations that lie in the solar path are called zodiac constellations. They are Aries, Tauras, Gemini, cancer, leo, Virgo, Libra, Scorpio, Saggittarius, Capricon, Aquarius and Pisces. Fig: Zodiac constellation Fig: Constellation in northern sky Activity 5 Use cardboards to make a the symbols of zodiac constellations. Also write their names in english and Nepali culture.

314 Oasis School Science and Technology - 8 Differences between Galaxy and Constellation S.N. Galaxy S.N. Constellation 1. It is a collection of billions of stars. 1. It is a collections of limited number of stars. 2. It has no regular pattern. 2. It has a regular pattern. 3. There are about 1011 galaxies in the universe. 3. There are 88 constellations named so far. Differences between Meteors and Stars S.N. Meteors S.N. Stars 1. They are made up of stone, iron or both. 1. They are made of gases mainly hydrogen and helium. 2. They are non-luminous bodies. 2. They are luminous bodies. Minerals Minerals are useful substances that are found in the crust of the earth. They are metallic or non-metallic solids found naturally in the earth's crust. The chemical compound which are inorganic, solid and has a definite chemical composition is called mineral. Some of them are metallic and rest are non-metallic. Some minerals are even fossils. All the minerals are unique. Types of Minerals a. Metallic minerals The minerals that contain significant amount of metals are called metallic minerals. However, the minerals from which metals can be obtained profitably are called ores. Ores contain less amount of impurities and higher amount of metals. Metallic minerals are the compounds of metals. For example: iron oxide, aluminium oxide, copper pyrites, limestone, dolomite, etc. Haematite, magnetite, limonite, etc. are ores of iron, bauxite is an ore of aluminium and copper pyrites is an ore of copper similarly, argentite is an ore of silver. From these ores we can obtain metals easily and profitably. Some metallic minerals are ferrous which has more iron concentration, non-ferrous minerals which has no iron concentration or precious minerals such as gold, silver and platinum. Fig: metallic minerals Fact File Coal is also a mineral even though it was made from plant parts.

Oasis School Science and Technology - 8 315 Reasonable Facts Bauxite is called metallic mineral. Bauxite is called metallic mineral because it contains maximum concentration of aluminium. b. Non-metallic minerals The minerals that do not contain significant amount of metals are called non-metallic minerals. Most of the non-metallic minerals are metallic compounds while some are nonmetallic compounds. Non-metallic minerals cannot be used to extract metals. They are mostly used for manufacturing cement, fertilizers, pesticides, gems and other decorative items. Examples of nonmetallic minerals are granite, slate, sulphur, silica, feldspar, quartz, obsidian, etc. Some non-metallic minerals such as sapphire, topaz, emerald etc. are gemstones. c. Energy minerals The minerals that can be used as fuel are called energy minerals. It could be petroleum. They are actually fossil minerals. They are carbon compounds preserved underground since ancient times. It is used to power vehicles and industries. Uranium is also an energy mineral which is used in nuclear power plant. Characteristics of minerals Minerals have their own distinct characteristics. Most minerals can be characterized and classified by their unique physical properties such as hardness, lustre, colour, streak, specific gravity, cleavage, fracture, and tenacity. i. Hardness Minerals can resist being scratched. Some minerals such as talc and gypsum are soft. They are scratched easily. Some minerals such as quartz, topaz and diamond are hard. They cannot be scratched easily. ii. Lustre The property of minerals to reflect light is called lustre. Metallic minerals such as gold, silver and galena have metallic lustre. Minerals such as Kaolin and limonite are earthy. They do not have lustre. iii. Colour Minerals are available in various colours. Gold is yellow, copper is red, feldspar is pink and haematite the ore of iron is reddish. Fig: non-metallic minerals Fact File The silicate minerals compose more than 90% of earth’s crust.

316 Oasis School Science and Technology - 8 iv. Streak Streak is the colour seen when the mineral is powdered. Minerals can make a streak when rubbed on a streak plate. The yellow streak means gold. Black streak means chalcopyrite, the ore of copper. v. Specific gravity Specific gravity is the ratio of the mass of minerals to the mass of the same volume of water. The specific gravity of water is 1, aluminium is 2.7 and gold is 19.32. vi. Tenacity The property of minerals to resist breakage is called tenacity. Quartz, feldspar, calcite and dolomite are brittle minerals. They break easily. Gold and silver are malleable and ductile. They can be hammered into a sheet and drawn into wires. Talc is sectile. It can be carved by knife. Biotite mica is elastic. It can regain its shape if we stop bending it. Gypsum is plastic. It does not regain its shape when we stop bending it. vii. Other characteristics of minerals Some minerals are transparent or translucent or opaque, magnetic or non-magnetic, crystalline or amorphous,regular shape orirregular shape, salty or bitter ortasteless and break along smooth plane (cleavage) or not. Reasonable Facts Minerals are inorganic substances. Minerals are inorganic substances because they are made of non-living materials only. Activity 6 Observe your surrounding and see if you find any minerals. Note its name. Uses of minerals Minerals are heavily used in construction of infrastructure, manufacture of tools and weapons and making utensils. They are also used to make medicine and fertilizer. Appropriate use of minerals can bring prosperity to the country. Gold is used to make ornaments Iron is used to make pipes and rods Silica is used to make glasses Fig: use of minerals

Oasis School Science and Technology - 8 317 Major uses of minerals are listed below : i. Minerals like gold, silver, platinum and diamond are used to make ornaments. ii. Minerals such as copper and aluminium are used to make electrical wires. iii. Minerals such as iron, copper and aluminium are used in construction of buildings, utensils and furniture respectively. iv. Aluminium is used to make the body of vehicles, cans, foils and cosmetics. v. Iron is used to make agriculture tools, machines and wedges. vi. Fossil minerals such as coal, petrol, natural gases and kerosene are used as a source of fuel for kitchens, vehicles and factories. vii. Limestone, clay and gypsum are used to make cement. viii. Limestone, silica and different other minerals are used to make glasses. ix. Kaolin is used to make ceramics. x. Fertilisers, fungicides and pesticides are manufactured from petrochemicals. xi. Slate, marble, granite and stones are used for roofing, flooring and making walls. xii. Fluorides are used in toothpaste. Reasonable Facts Gold is used to make ornaments. Gold is used to make ornaments because it is shiny, malleable and rust-free. Activity 7 Observe the various minerals used in your house. Important minerals found in Nepal Minerals are metallic or non-metallic solids found naturally in the earth's crust. Different types of minerals are found in different parts of our country. More than 60 different types of minerals are discovered in Nepal. Hilly region contains 83% of minerals found in Nepal. Minerals like limestone, magnesite, lead, zinc, copper, iron, marble, etc. are found in Nepal. It is estimated that about 7 crore tons of limestone, which is used in making cement, can be obtained in Udaypur and Sindhuli. Limestone can also be Fact File A rock is a combination of multiple minerals. Fact File Nepal has 21 types of metallic minerals, 23 types of insulator and fertilizer type mineral, 6 types of gem stones types minerals, 9 types of minerals that can be used for construction, 4 types of fossil minerals.

318 Oasis School Science and Technology - 8 found in Surkhet and Chobhar of Kathmandu. About 1 crore 53 lakh tons of limestone can be obtained from Chobhar. About 80 lakh tons of limestone is located in Bhaise and about 1 crore tons of limestone is located in Okhre of Makawanpur district. Limestone is used in cement factories. Agricultural lime and chemical lime can also be produced from limestone. It is estimated that ores of iron are found in Lalitpur, Ramechhap, Rolpa, Tanahu and Chitwan. However, iron has not been extracted so far from those places. About 10 lakh tons of iron is supposed to be present at Phulchoki in Laliptur. It is also estimated that 1 lakh 40 thousand tons of copper is present at Kalitar in Makawanpur and about 1 lakh 74 thousand tons of copper at Wapsa in Solukhumbu. Similarly, it is estimated that there is a presence of 78 thousand tons of lead and zinc is in Ganesh Himal of Rasuwa, 28 lakh tons of lead and zinc in Lawang and Khairang of Dhading. It is also estimated that there is a presence of 30 crore cubic metres of natural gas in Kathmandu valley. Proper extraction and utilization of these minerals will be helpful in the economic development of our country. Reasonable Thinking Skill R T S 1. Differentiate between metallic minerals and non-metallic minerals. The differences between metallic minerals and non-metallic minerals are: SN Metallic minerals SN Non-metallic minerals 1 The minerals that contain a higher concentration of metals are called metallic minerals. 1 The minerals that contain very less or no concentration of metals are called non-metallic minerals. 2 It can be used to extract metals. 2 It cannot be used to extract metals. 3 They are usually denser. 3 They are usually less dense. 2. Wise use of minerals can bring prosperity to the country. Wise use of minerals can bring prosperity to the country in the following ways: i. Minerals can be used as raw materials for industries. ii. Mining, transporting and processing minerals can create jobs. iii. Many people can earn a livelihood. iv. Raw minerals or finished products can be used within the country or sold abroad. 3. All ores are minerals but all minerals are not ores. All ores are minerals because all of them contain useful elements or compounds for us. But not all minerals are ores because most of them cannot be used to extract useful substances on a profitable scale.

Oasis School Science and Technology - 8 319 4. Recycling minerals is very important. Recycling minerals is very important because minerals are non-renewable. We must recycle minerals so that these mines can last for the future generation. 5. Discuss the importance of minerals. The importance of minerals are: i. Minerals are used for extracting metals that are used for making utensils. ii. Minerals such as sand, conglomerate and mica are used for construction. iii. Some minerals are used as ornaments. iv. Minerals are absorbed by plants which are very important for our body. 7. Haematite is called a metallic mineral. Haematite is called a metallic mineral because it contains a very high concentration of iron metal. 6. Comets are called tailed stars. Comets are called tailed stars because since they are made of ice, they evaporate as they approach the sun and form a very long tail. 7. How do comets terminate? The comets terminate if they are completely melted by the sun or collide with planets. 8. Meteorites are dangerous to us. Meteorites are dangerous for us because they hit the earth. The collision can bring devastating earthquakes, fire and tsunamis and destroy the continents. 9. Differentiate between comet and asteroid. The differences between comets and asteroids are: SN Comet SN Asteroid 1 The comet is a chunk of ice that revolves around the sun. 1 The asteroid is an irregular rock that revolves around the sun. 2 Comets are made of frozen gases and dust. 2 Asteroids are made of rock and metal. 10. Most meteors do not hit the earth. Most meteors do not hit the earth because as they enter the earth, they have to penetrate the atmosphere. Due to the friction between meteors and the atmosphere, they start to burn and finish.

320 Oasis School Science and Technology - 8 Exercises 1. Choose the best answer from the given alternatives. a. Which heavenly object is called a tailed star? i. asteroids ii. comets iii. meteor iv. satellites b. Which heavenly object is called a shooting star? i. asteroids ii. comets iii. meteor iv. satellites c. What is a meteor that hit the earth called? i. meteoroid ii. meteorite iii. meteor shower iv. fireball d. What is a group of billions of stars called? i. galaxy ii. universe iii. constellation iv. stellar nursery e. What type of mineral is argentite? i. metallic mineral ii. non-metallic mineral iii. fuel minerals iv. useful minerals 2. Define the following terms with required examples. a. Universe b. Astronomy c. Kuiper belt d. Planets e. Asteroid belt f. Coma g. Exocomet h. Meteoroids i. Near-earth asteroid j. Endocomet k. Non-metallic minerals l. Big bang theory 3. Very short questions a. What is a very huge and bright meteor called? b. Give any two examples of spiral galaxies. c. What are the constituents of iron meteorite? d. What is rock floating in space that could enter the earth’s gravitational field called? e. What is the average velocity of a meteor? f. Write the names of the smallest and largest constellations. g. What are extinct comets? 4. Give reasons. a. Asteroids are called minor planets. b. Comets are called tailed stars. c. Meteors are called shooting stars.

Oasis School Science and Technology - 8 321 d. Tail of the comet grows longer near the sun. e. Comet and asteroids are not a star. f. Some comets never return. g. Jupiter saves the earth from comets and meteoroids. h. Meteorites are a threat to humans. i. We should recycle minerals. j. Argentite is called a metallic mineral but gypsum is non-metallic. k. Wise use of minerals can bring prosperity to the country. 5. Differentiate between : a. Meteors and meteorites b. Asteroids and comets c. Iron meteorite and stone meteorite d. Spiral galaxies and elliptical galaxies e. Galaxy and constellation f. Metallic and non-metallic minerals 6. Short questions. a. Mention the conditions in which a comet will be terminated. b. Clarify the concept of the big bang theory. c. What is the importance of constellations for astronomers? d. What is a zodiac constellation? e. Mention any four properties of the mineral. f. Minerals have a very important role in the development of the country. 7. Long questions. a. Write a short note on the milky galaxy. b. Describe the structure of the comet. c. Describe various types of meteorites. d. What is a galaxy? Describe its types with two examples of each. e. Write down the importance of observation of constellations in our daily life. f. What is a mineral? Describe its types with suitable examples. g. What are minerals used for? Write any four important uses of minerals in our society. h. Write a short essay on ‘important minerals found in Nepal.’

322 Oasis School Science and Technology - 8 Key terms and terminologies 1. Planetesimal hypothesis : According to this hypothesis, the earth along with other planets and satellites was formed when a comet revolving around the universe struck the sun millions of years ago. 2. Nebular hypothesis : According to this hypothesis, the whole of our solar system, including other heavenly bodies, was in the form of a nebula, which condensed, formed eddy current, rotated and formed huge core. The core changed into star and the detached outer ring solidified into planets and satellites. 3. Tidal hypothesis : According to the hypothesis given by Jeans and Jeffrey in 1917 AD, a big star orbiting around the sun finally approached it. A large mass of gas was ejected from the sun due to the tidal effect. In the course of cooling, the tidal matter fragmented into small pieces forming planets, satellites, etc. As a result, the solar system was formed. 4. Geological time scale : The time scale that represents any event that has happened on the earth from its origin to the current time is called the UNIT 11.2 EVOLUTION OF LIFE ON THE EARTH Estimated teaching periods Theory 2 Practical 1  Introduction to the history of the earth  Some hypotheses about origin of the earth  (George wofan hypothesis, Nebular hypothesis, Tidal hypothesis and Dust and cloud hypothesis)  Some important facts about the earth  Geological time scale, introduction of four era  Evolution of life The Sequence of Curriculum Issued by CDC George Buffon is well known for his old planetesimal hypothesis. He was born in France on 7th September 1707 and died on 16th April 1788. He was a French naturalist, mathematician, cosmologist and encyclopaedist. He was the first naturalist to recognize ecological succession, geological history and animal evolution. He also proposed that earth, along with other planets and satellites was formed when a comet moving around the universe stroke the sun millions of years ago. About the Scientist George Buffon

Oasis School Science and Technology - 8 323 geological time scale. 5. Eon : Eons are the primary and largest periods of geological time scale. 6. Epoch : Epoch is the smallest period of geological time scale. 7. Era : The further division of eon is era. 8. Precambrian era : The duration from the origin of the earth to the phanerozoic eon is called the Precambrian era. 9. Palaeozoic era : The duration from 570 million years to 250 million years when the first fish and first land plants evolved is called the Palaeozoic era. 10. Mesozoic era : The duration from 250 million years ago to 65 million years ago when various reptiles dominated the earth is called the Mesozoic era. 11. Cenozoic era : The duration from 65 million years ago onward when various mammals including us evolved is called the Cenozoic era. 12. Evolution of life : The process in which primitive living things slowly but gradually modify, adapt and change into newer species after millions of years is called evolution of life. Introduction The earth is one of the members of the solar system. It originated along with other planets, but only on the earth’s surface is the climatic condition suitable for the survival of living organisms. The branch of science in which we study about the earth is called geology. The question about the origin of the earth remains unsolved. Many scientists have put forward their own opinions regarding the origin of the earth. But no universal theory of the origin of the solar system has been proposed yet. Some of the hypotheses regarding the origin of the earth and solar system are discussed below: 1. Planetesimal hypothesis or George Wofan's hypothesis A French scientist, George Wofan, put forward a hypothesis in 1749 AD. According to this hypothesis, the earth along with other planets and satellites were formed when a comet revolving around the universe struck the sun millions of years ago. Features of planetesimal hypothesis i. The planets were very hot in the beginning but cooled down later as they went far from sun. ii. All the celestial objects in solar system must have come out of sun because there total mass does not sum up to even 1 % of solar mass. Fact File Planetisimal hypothesis is modified into new planetisimal hypothesis where a star passed near by the sun, created a bulge, which changed into planets.

324 Oasis School Science and Technology - 8 2. Nebular hypothesis or Kant Laplace nebular hypothesis A German philosopher, Immanuel Kant, in 1755 AD put forward another hypothesis which is called nebular hypothesis. It was modified by a French mathematician Laplace in 1796 AD. According to this hypothesis, the whole of our solar system, including other heavenly bodies, was in the form of a nebula, i.e., an extremely large mass of gas and dust. The nebula began to contract due to its own gravity. During this process, an outer ring was detached from the central core, which started to revolve around the central core. The masses began to collide with one another and broke into small masses due to the effect of gravitation. These small masses began to revolve around the central mass. This central mass became the sun, and other revolving bodies became planets and satellites, including the earth. Features of nebular hypothesis i. Planets were cold to begin with. Some of them might have melted in early stage due to collision with meteorites. ii. Since the planets and dwarf planets were formed from ejected materials of rotating nebula, all of them revolve around the sun from same plane. 3. Tidal hypothesis or Jeans and Jeffery’s hypothesis According to the hypothesis given by Jeans and Jeffrey in 1917 AD, a big star orbiting round the sun finally approached it. A large mass of gas was ejected from the sun due to the tidal effect. In the course of cooling, the tidal matter fragmented into small pieces forming planets, satellites, etc. As a result, the solar system was formed. Features of tidal hypothesis i. The tide was tapered on both ends. So planets near the sun and the planets far away from the sun are small. And the planets in the middle regions are bigger. ii. Mars was supposed to be bigger than the earth but it is smaller. It may be smaller than the earth because its certain part broke off from it. 4. Binary hypothesis The binary hypothesis is proposed by Thomas Chrowder Chamberlin and Forest Ray Moulton. According to hypothesis ' our solar system had two stars which were rotating each

Oasis School Science and Technology - 8 325 other. There was another star far bigger than the sun. That star suddenly flew very close to the sun and ejected tides. The tides formed in the sun at that moment break from sun, cooled down and changed into planets and satellites. However, there is no sign that the sun ever had a binary star. Geological Time Scale The time scale that represents any event that has happened on the earth from its origin to the current time is called the geological time scale. On the basis of existence of living beings, the geological history is divided into four parts. They are eon, era, period and epoch. Eon is the longest duration of time, i.e., billions of years, in the geological history which is divided into eras. The entire geological history has been divided into four eons. They are Hadean eon (4.5 to 4 billion years ago), Archean eon (4 to 2.5 billion year ago), Proterozoic eon (2500 to 541 million years ago) and Phanerozoic eon (541 million years ago to recent). Some geologists also classify geological time scales into two eons. They are Cryptozoic eon (4.6 billion years ago to 570 million years ago) and phanerozoic eon (570 million years ago onward). They divide cryptozoic eon into Archeozoic era, proterozoic era and eozoic era. Sometimes cryptozoic eon is also called azoic era or precambrian era. Phanerozoic eon is divided into three eras. They are Paleozoic era, Mesozoic era and Cenozoic era. In this unit, we will study about four geological eras. A geological era is a division of an eon in which important changes took place. The entire geological history is divided into four geological eras. They are as follows: 1. Precambrian era (4.5 billion years ago to 570 million years ago) 2. Palaeozoic era (57 million years ago to 250 million years ago) 3. Mesozoic era (250 million years ago to 65 million years age) 4. Cenozoic era (65 million years ago to recent) 1. Precambrian era The duration of this era was 4.5 billion years to 570 million years ago. In this era, the origin of the earth took place. There was no existence of living beings before 3.8 billion years ago. Rocks like gneiss and granite were formed in this era. Bacteria evolved about 3.8 years ago and algae came into existence about 3.2. billion years ago. There is evidence of the dominance of invertebrates at the end of this era. 2. Palaeozoic era The duration of this era was in between Fact File The largest unit of the geological time scale is the eon whereas the smallest one is the epoch. Fact File Precambrian era is as long as first 3 eon (Hadean eon, archean eon and proterozoic eon). The phanerozoic eon is divide into Palaeozoic era, Mesozoic era and Cenozoic era. Fact File Palaeozoic era is called age of pisces.

326 Oasis School Science and Technology - 8 570 million years ago to 250 million years ago. This era has been divided into six periods. They are the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. The main events of this era are as follows: i. Sedimentary rocks were formed in this era. ii. Change in weather and atmosphere took place. iii. Fossils of different types of animals and plants were formed. iv. Aquatic and terrestrial invertebrates and vertebrates were formed in cambrian period. For example: winged insects, fishes, amphibians, trilobites, molluscs, snails, scorpion, frog and first reptiles. v. Different types of green plants like bryophytes and pteridophytes were formed. For example, fern and lycopodium. Reasonable Facts The end periods of Palaeozoic era are called age of amphibians. The end periods of Palaeozoic era are called age of amphibians because multiple species of amphibians evolved and lived on coastal areas in that era. 3. Mesozoic era The duration of this era was in between 250 million years ago to 65 million years ago. In the Mesozoic era, a large number of reptiles evolved on the land and sea. Therefore, Mesozoic era is also called the golden era of reptiles. This era is divided into three periods. They are the Triassic period, Jurassic period and Cretaceous period. The main events of the Mesozoic era area as follows. i. Different types of hills and mountains were formed in the Mesozoic era. ii. Climatic condition was suitable to sustain aquatic, terrestrial and aerial animals like dinosaurs, tortoises, toothed birds, etc. iii. Evolution, development and extinction of dinosaurs and other huge reptiles took place. iv. Coniferous plants such as ginkgo, ephedra, cycas and pines were developed in this era. It is also called age of conifers. v. Mammals began to evolve at the end of this era. Fig. Dinosaurs Fact File Multiple species of dinosaurs evolved in Triassic period, become dominant in Jurassic period and become extinct in Cretaceous period. Most dinosaurs went extinct due to meteor shower, natural disasters, forest fire and air pollution. Dust and smoke covered the sky and made air poisonous for many years which killed almost all dinosaurs.

Oasis School Science and Technology - 8 327 4. Cenozoic era The duration of this era is in between 65 million years ago to the present. It is also known as recent era or era of human beings or age of mammals or age of angiosperm. This era has been divided into seven periods. They are the Paleocene period, Eocene period, Oligocene period, Miocene period, Pliocene period, Pleistocene period and Holocene or recent period. The main events of this era are given below: i. Evolution of early human beings took place in this era in Miocene epoch 6 million years ago. New species humans that walked in two feet evolved 4 million years ago. Modern humans and Homo sapiens also called cromagnons evolved 56,800 years ago. Human ancestors lived through stone age, bronze age, iron age and lastly the agriculture and animal husbandry since last 11,700 years ago. ii. Breaking and expansion of rocks, volcanic eruptions, etc. took place in this era. iii. The climatic condition was changing with decreasing temperature. As a result, mountain peaks were covered with ice. iv. Neanderthal man, toothed animals, gymnosperms and angiosperms evolved. Reasonable Facts Humans evolved later than the dinosaurs. Humans evolved later than the dinosaurs because the environment was not suitable for humans but was better for the evolution of dinosaurs. Reasonable Facts Origin of earth and human beings did not occur at the same time. The study of the radioactivity of rocks and fossils of human beings present on the earth provides evidence that the origin of the earth and human beings did not occur at the same time. Reasonable Facts Why is the Mesozoic era called the golden age of reptiles? In the Mesozoic era, there was the dominance of various types of large reptiles like dinosaurs, turtles, etc. on land and marine water. Therefore, the mesozoic era is also called the golden age of reptiles. Reasonable Facts Living beings evolved after millions of years of the formation of the earth, why? The earth evolved about 4.5 billion years ago. At the time of evolution of the earth, it was very hot and there was no suitable environment for the evolution and survial of living organisms. So there were no life at the time of the evolution of the earth.

328 Oasis School Science and Technology - 8 Evolution of Life About 600 million years ago, there was no favourable environment for the evolution of organisms on the earth. After continuous change in the climatic condition, it became favourable to support/sustain life. Hydrogen, nitrogen and oxygen combined in a suitable way to form biomolecules which evolved into simple prokaryotes. Continuous evolution gave rise to eukaryotes. During the course of evolution, various kinds of organisms evolved, developed and became extinct. The organisms which became extinct from the earth left some evidences called fossils on the sedimentary rocks. Afterthe complete study and analysis of these fossils, scientists discovered the process of evolution of life on earth. In the Precambrian era, there were no or very less fossils in sedimentary rocks, which indicates that evolution of life did not take in early stage but evolution started gradually over time. In this era, evolution of unicellular organisms and development of multicellular organisms took place. In the Palaeozoic era, rainfall occurred after various change in water, land and weather, which created a favourable condition for the evolution and development of organisms. In the Palaeozoic era, different types of aquatic as well as terrestrial animals evolved. Fishes, amphibians and some primitive reptiles evolved and well developed in this era. In the Mesozoic era, several types of reptiles like dinosaurs, toothed birds evolved, developed and became extinct also. So, the Mesozoic era is also called the age of reptiles or the age of dinosaurs. In the Cenozoic era, primitive humans evolved. Many mammals like the cat, rat, dog, elephant, crocodile, bat, etc. evolved and developed. A brief description of the geological history and evolution of life is summarized in the given table. This description is based on the book "The ICC's Geologic Time Scale, 2012". Geological history and evolution of life Era Duration Evolution of life Precambrian 4.5 billion years ago to 57 crore years ago Origin of the earth Evolution of unicellular organisms and development of multicellular organisms Palaeozoic 57 crore years ago to 24 crore years ago Development of a few marine organisms Development of vertebrates in marine water Evolution of life on land, green vegetation and development of fishes Evolution of winged insects, development of fishes and plants Evolution of amphibians and reptiles, development of fern plants Extinction of many invertebrates and vertebrates, development of reptiles

Oasis School Science and Technology - 8 329 Mesozoic 24 crore years ago to 6 crore 50 lakh years ago Evolution of dinosaur, reptiles and coniferous plants Dominance of reptiles, well developed dinosaurs, birds and other organisms Evolution of flowering plants and different insects, extinction of dinosaurs and other large reptiles Cenozoic 6 crore 50 lakh years ago to the present Evolution of first mammal and horse Development of various mammals like elephant, whale, etc. and development of owl Evolution of sharp-toothed cats and monkeys Development of grasses Evolution of human beings Development of Stone Age human beings and giant hairy elephants, i.e., mammoths Development of modern human beings and other mammals, dominance of human beings Some facts about the earth • The Earth is estimated to be around 4.5 billion years old. • The Earth is the third planet from the Sun and the only known planet to support life. • It has a diameter of approximately 12,742 kilometers and a mass of 5.97 x 1024 kg. • The Earth has an atmosphere that consists mainly of nitrogen (78%) and oxygen (21%). • The Earth rotates on its axis once every 24 hours, which causes day and night. • It takes approximately 365.25 days for the Earth to orbit around the Sun. • The highest point on Earth is Mount Everest, which stands at 8,848 meters above sea level. • The lowest point on Earth is the Challenger Deep, located in the Mariana Trench in the Pacific Ocean, which is 10,924 meters deep. • The Earth has a natural satellite, the Moon.

330 Oasis School Science and Technology - 8 Reasonable Thinking Skill R T S 1. Why was the planetesimal hypothesis discarded? The planetesimal hypothesis was discarded because a comet, which is made of ice, would probably melt before hitting the sun. 2. How did the solar system come to be according to Kant and Laplace? According to the Kant and Laplace hypothesis, the solar system was formed from a very huge nebula that condensed and rotated the core. The core condensed into a protostar and then into the sun. The outer ring separated from the core and condensed into multiple planets and satellites. 3. How do we come to know about ancient lives that once lived on the earth? We learn about the ancient lives that once lived on the earth by observing the fossils that are found in multiple layers of sedimentary rocks. 4. Palaeozoic era is called the age of fishes. The Palaeozoic era is called the age of fishes because multiple species of fishes evolved and dominant in the ocean in this era. 5. Mesozoic era is called the golden age of reptiles. The Mesozoic era is called the golden age of reptiles because multiple species of reptiles including dinosaurs evolved and roamed all over the earth during the Mesozoic era. 6. Cenozoic era is called the age of mammals. The Cenozoic era is called the age of mammals because multiple species of mammals including humans evolved in the Cenozoic era. 7. How do we know that the first life came in water? We know that first life came in water through the study of fossils. The oldest fossils ever found belong to aquatic animals which means the first life originated in waters. 8. When did the following species evolve? Cats, monkeys, archaeopteryx, dunkleosteus fish i. Cats evolved in the Cenozoic era. ii. Monkeys evolved in the Cenozoic era. iii. Archaeopteryx evolved in the Mesozoic era. iv. Dunkleosteus fish evolved in the Palaeozoic era.

Oasis School Science and Technology - 8 331 Exercises 1. Choose the best answer from the given alternatives. a. Who proposed the planetesimal hypothesis? i. George Wofan’s hypothesis ii. Immanuel Kant iii. James Jeans iv. Harold Jeffrey b. Which age is called the ages of reptiles? i. Precambrian era ii. Palaeozoic era iii. Mesozoic era iv. Cenozoic era c. Who proposed the Tidal hypothesis? i. George Wofan ii. Immanuel Kant iii. Jeans and Jeffrey iv. Laplace d. What is the estimated age of the earth? i. 13.8 billion years ii. 4.5 billion years iii. 2 million years iv. 10,000 years e. In which era human beings were evolved? i. Precambrian era ii. Palaeozoic era iii. Mesozoic era iv. Cenozoic era 2. Define the following terms with required examples. a. Planetesimal hypothesis b. Nebular hypothesis c. Tidal hypothesis d. Geological time scale e. Eon f. Era g. Precambrian era h. Palaeozoic era i. Mesozoic era j. Cenozoic era 3. Very short questions a. Which era is called the era of creepers? b. Name the era in which whales evolved. c. Name the era in which fish, winged insects, ferns, coal forests, modern humans, flowering plants and dinosaurs evolved. d. What is the largest unit of geological history? e. Into how many eras is the evolution of organisms on the earth divided? f. What is the duration of the Mesozoic era, Palaeozoic era, Cenozoic era and Precambrian era? 4. Give reasons. a. Palaeozoic era is called the age of Pisces.

332 Oasis School Science and Technology - 8 b. Mesozoic era is called the age of creepers. c. Cenozoic era is called the age of mammals. d. Origin of earth and living beings did not occur at the same time. e. First life originated in water. f. Fossils are very important to understand the evolution of life. g. Humans evolved later than the dinosaurs. h. Fossils are not found in igneous rock. 5. Differentiate between : a. Planetesimal hypothesis and nebular hypothesis b. Precambrian era and Palaeozoic era c. Cenozoic era and Mesozoic era 6. Short questions. a. How is the solar system formed based on the Planetesimal hypothesis? b. Write a short note on binary star hypothesis of origin of solar system. c. What is a geological time scale? Enlist its four eras. d. Write a short note on the Precambrian era. e. Enlist the main incidents that happened in the Palaeozoic era. f. What are the main events that occurred in the Mesozoic era? g. Enlist the main events of the Cenozoic era. h. How is it known that there were dinosaurs on the earth in ancient times? In which era were they dominant? 7. Long questions a. Describe the formation of the solar system based on the Kant-Laplace Nebula hypothesis. b. Clarify Jeans and Jeffreys tidal hypothesis of the origin of the solar system. c. Write a short essay on the evolution of life. d. Explain the evolution process that occurred in the Mesozoic and Cenozoic eras. Also, mention their differences.