One mark questions with answers

Q1. What do you mean by the differentiation of the earth?

Ans1. Formation of the layered structure of earth under the action of gravity is called differentiation of earth.

Q2. What is the name given to the region between the crust and the core of the earth?

Ans2. Mantle.

Q3. What does the mantle of the earth consist of?

Ans3. The region between the crust (Lithosphere) and the core of the earth is called Mantle. It goes from the base of the lithosphere to a depth of about 2900 km. It is made up mainly of Iron and Magnesium Silicates.

Q4. What is Magma? Give one cause for the volcanic eruptions.

Ans4. The material consisting of molten rocks and hot gases in the upper part of the mantle is called Magma.
Development of huge pressure inside the earth leads to volcanic eruptions.

Q5. Where do earthquakes occur frequently?

Ans5. Earthquakes occur near the faults in the rock formation or at place rocks at the joints interlock into one another.


Two mark questions with answers

Q1. What is meant by Differentiation? Name three major layers of earth.

Ans1. Differentiation : The reorganisation of molten primitive earth into three layers having different densities under the action of gravity is called differentiation of earth.
Different layers of the earth :
(i) The outermost layer, called crust.
(ii) The underlying layer, called mantle.
(iii) The central zone, called core.

Q2. How were the oceans formed?

Ans2. The gases liberated from the cooling molten rocks mainly consisted of carbon dioxide, nitrogen and water. These gases went up into the atmosphere, got condensed into clouds, and poured down as rain to fill up the low-laying areas. Thus, the oceans were formed.

Q3. State four conditions needed for the origin and flourishing of life on a planet.

Ans3. (i) Sufficient water.
(ii) Elements such as carbon, nitrogen, hydrogen and oxygen.
(iii) Moderate temperature.
(iv) Protective ozone layer to protect life from the harmful radiations coming from the outer atmosphere.

Q4. Give the importance of Lithosphere.

Ans4. Lithosphere mainly consists of rocky material of low density, minerals, coal, oil and natural gas. It is also the source of underground water on earth, and thus supports life on earth.


Three mark questions with answers

Q1. How is lithosphere constantly recycled?

Ans1. When the supporting plates of lithosphere crash into one another producing mountains, volcanoes and earthquakes, then a part of it falls down into magma in the mantle of earth. After melting this material becomes a part of magma. This magma comes out from the vents on the earth's surface and gets solidified in the form of rocks. In this way, the material removed from lithosphere during various processes is regenerated into the lithosphere after some time. This is recycling of lithosphere.

Q2. What makes the earth a special planet in the solar system?

Ans2. The land, seas and atmosphere of earth support a large variety of living organisms. It is the presence of life on earth which makes it a unique planet in the solar system. The life supporting environment on the earth developed because of its distance from the sun, its mass and its gravitational field.

Q3. Explain why there are no surface records of the records of the first 800 million years of the earth's existence?

Ans3. The solar system is believed to be about 4500 million years old. The rocks brought back from the moon were found to be about 4000 million years old. The oldest rock on earth is only 3700 million years old. This means that the first organisation of the earth would have taken place when it melted within 800 million years of its formation. So, there are no surface records of the first 800 million years of the earth's existence.

Q4. Why does Iron in the inner core of the earth remain in solid form despite high temperature?

Ans4. Inside the core, the pressure is extremely high. Increase of pressure causes an increase in the melting point of Iron. Therefore, even if the temperature is much above the normal melting point, Iron in the inner core remains in solid state.


Five mark questions with answers

Q1. Describe the evolution of life on earth.

Ans1. After the first organisation of the earth system when it melted within 800 million years of its formation, an atmosphere and water bodies were formed on the earth. The atmosphere at that stage contained mainly gases like carbon dioxide, nitrogen and hydrogen. The great rains, which formed the oceans on earth were accompanied by thunderstorms which produced violent electric discharges called lightning. The spark produced by lightning fused the chemical elements present in the atmosphere and oceans into complex molecules. These complex organic molecules became the building blocks of life. The complex molecules of carbon, hydrogen and nitrogen were washed down into oceans with rain water to form the first living organisms. These first revolutionary living organisms on the earth were blue green algae, which originated in oceans. The blue-green algae could utilise the sunlight energy to carry out the process of photosynthesis. The blue-green algae combined the carbon dioxide of sea and water in the presence of sun-light energy to form carbohydrate molecules for food and released oxygen gas during this process. As the atmosphere gradually got enriched with oxygen gas, more advanced forms of life evolved and could easily spread on land also.

Q2. What is "Green House Effect"? Explain it with the help of an example.

Ans2. The carbon dioxide gas in the atmosphere performs a major role called Green House Effect. The heating up of the earth's atmosphere due to the trapping of infra-red rays by carbon dioxide layer in the atmosphere is called green-house effect. The green house effect can be explained as follows : The sun-light consists of three parts. ultra-violet radiation, visible light and infra-red rays. The Ozone layer absorbs U.V. radiations from sun-light allows the visible light and infra-red rays to pass through it and reach the earth. Since the sun is very hot, the infra-red rays emitted by it are of short wave-length which easily pass through the carbon dioxide layer in the atmosphere. These infra red rays have heating effect due to which they heat the earth surface and the objects on it. Some of the infra-red rays are reflected back by the earth and its objects. But these reflected infra-red rays are of longer wavelength. Now, the carbon dioxide molecules present in the atmosphere have the ability to absorb the longer wavelength infra-red rays reflected from the earth. So, the blanket of carbon dioxide gas in the atmosphere traps the infra-red heat rays, causing the atmosphere to get heated up. This heating up of earth's atmosphere due to the trapping up of infra-red rays by carbon dioxide is called green house effect. An example of the green house effect from every-day life is that a car parked in sun-shine with its windows closed is found to be very hot inside. It is produced by the glass panes of the car windows. The glass panes of car windows trap the infra-red rays reflected from inside the car which results in the rise in temperature inside the car.

Q3. Describe the evolution of the atmosphere.

Ans3. The evolution of atmosphere is described below :

(i) When the primitive earth melted during differentiation, the Iron and some other heavy elements like Nickel, sank towards the outer layer called mantle which consisted of partially molten rocks. The lightest materials present in primitive earth were expelled as gases and these gases formed the first atmosphere of earth.

(ii) As the molten earth cooled, the outer surface of mantle solidified to form crust. The primitive crust was repeatedly punctured by meteorites falling from outer space. Since the atmosphere at that stage was very thin, it could not slow down the falling meteorites. So, the meteorites continued to fall on the earth with great force and formed vents in the crust of earth. Then molten rocks from the mantle rushed to the earth's surface through these vents. They released more gases into the atmosphere. At this stage, the atmosphere contained mainly gases like carbon dioxide, nitrogen and water vapour. The early atmosphere did not contain oxygen gas in it.

(iii) Around 2 billion years ago, the first living organisms like blue-green algae started doing photosynthesis and released oxygen gas into the atmosphere. This way, oxygen became the second most abundant gas in atmosphere, after nitrogen.

(iv) Some of the oxygen was converted into Ozone by the action of sun-rays. This Ozone formed a protective layer in atmosphere around the earth which cut off harmful ultra-violet radiations coming from the sun.

(v) The oceans removed excess of carbon dioxide from the atmosphere by dissolving it in ocean water. The reduction of carbon dioxide in the atmosphere reduced the temperature of atmosphere by reducing the green-house effect. Thus, about 0.6 billion years ago, our atmosphere had evolved fully which was quite comfortable for life.

Q4. What would have happened if the earth had more mass or less mass than its present mass?

Ans. (Try yourself).

Q5. Explain the structure of different layers of earth.

Ans. (Try yourself).

Q6. What is "Pangea"? Draw sketches to illustrate your answer.

Ans. (Try yourself).