Earth as a Planet

At the Bedford level canal area a famous experiment was carried out. How many poles were used and at what distance apart?

1. 3 poles, 5km
2. 2 poles, 10km
3. 4 poles, 5km
4. 3 poles, 10km

Answer

3 poles, 5 km

Reason — The Bedford Level experiment used 3 poles of equal height spaced 5 km apart along a straight canal.

You are inside a hot air balloon floating at 500 m above the ground. What would you say about the view of the earth's surface as you see it?

1. square
2. rectangular
3. circular
4. triangular

Answer

circular

Reason — As the balloon floats at 500 m above the ground, the earth's surface appears circular. This is possible only because the earth is spherical in shape.

Assertion (A): With increase in altitude the circular horizon of the earth's surface also widens.

Reason (R): The earth's surface is flat.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is true but R is false.

Explanation — With increase in altitude the circular horizon also widens. Had the earth's surface been flat the horizon would have been the same irrespective of altitude.

At what angle can the Pole Star be seen at Macapa, Brazil? [Hint: It lies on the equator]

1. 60°
2. 90°
3. 45°
4. 0°

Answer

0°

Explanation — Macapa, Brazil lies on the Equator where the altitude of the Pole Star is 0°. Because the Pole Star aligns with the Earth's rotational axis, its angle of elevation decreases from 90° at the North Pole down to 0° at the Equator, making it visible exactly on the horizon at Macapa.

Assertion (A): The pole star lies in line with the axis of the earth with its angle decreasing towards the Equator.

Reason (R): The earth is spherical in shape.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — The Pole star can be seen at 90° at the North pole and at 0° at the Equator. As the pole star lies in line with the axis of the earth, its angle decreases when one moves towards the Equator because of Earth's spherical shape.

In 1522 Magellan's ship Victoria returned to Spain. What did this voyage prove?

1. The earth is spherical
2. The earth is flat
3. The earth is rectangular
4. The earth is triangular

Answer

The earth is spherical

Explanation — Magellan's ship Victoria completed a round-the-world voyage in 1522 and returned to the same place from where it had started (Spain). This proved beyond doubt that the earth's surface is round (spherical).

Ancient cultures took earth for a disk, but very soon the observation of stars and planets revealed that earth resembles a sphere. After the late 1700s measurements showed that earth is slightly flattened at the poles. What is the actual shape of the earth?

1. Sphere
2. Oblate
3. Oval
4. Oblate Spheroid

Answer

Oblate Spheroid

Reason — The earth is not a perfect sphere. It bulges at the Equator and is flattened at the Poles due to the centrifugal force of its rotation at great speed. Hence, the actual shape of the earth is an oblate spheroid.

Given below are pairs of statements. Select the statements which prove the spherical shape of the earth.

1. If there were no buildings in the way, we would be able to see another city that is hundreds of miles away.

2. The boat would stay in view no matter how far out to sea it went.

3. A ship slowly starts to disappear from view as it gets farther away.

4. If we were to place two identical sticks in the ground in two different places, the length of their shadows differs.

5. During a lunar eclipse, the sun projects Earth's shadow onto the moon and the shadow is round.

6. 1, 2, 3

7. 2, 3, 5

8. 3, 4, 5

9. 1, 4, 5

Answer

3, 4, 5

Reason — Statements 3, 4 and 5 prove the spherical shape of the earth — a ship gradually disappears from view as it moves away (curved surface), the shadows of two identical sticks differ in length at different places, and during a lunar eclipse the earth casts a round shadow on the moon. Statements 1 and 2 would be true only if the earth were flat.

Which gas dominates the atmosphere of Venus?

1. Oxygen
2. Carbon dioxide
3. Nitrogen
4. Helium

Answer

Carbon dioxide

Reason — The atmosphere of Venus is mainly composed of carbon dioxide, which produces a greenhouse effect on its surface. This keeps the temperature of Venus very high and makes it hotter than Mercury.

Earth happens to orbit the sun within the so-called "Goldilocks zone," where temperatures are just right to maintain liquid water on our planet's surface. Water covers roughly 71% of Earth's surface, with most of that water located in our planet's ............... .

1. Ice-caps
2. Glaciers
3. Oceans
4. Rivers

Answer

Oceans

Reason — Earth is a watery planet with about 70 per cent of its surface covered by water, and most of this water is located in the oceans. Hence, the earth appears blue from space.

Assertion (A): Water on earth drastically tones down day and night temperature variation.

Reason (R): Water can absorb enormous amount of heat without causing much change in its temperature.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — Water has a high specific heat capacity, meaning it can absorb or release a large amount of heat energy with minimal change to its own temperature. This characteristic allows Earth's oceans and water bodies to act as thermal buffers, absorbing heat during the day and releasing it at night, which drastically tones down global temperature extremes.

Name the gas that absorbs the harmful ultraviolet rays of the sun.

1. Ozone
2. Oxygen
3. Carbon dioxide
4. Nitrogen

Answer

Ozone

Reason — Ozone present in the earth's atmosphere absorbs the harmful ultraviolet rays of the sun, thus protecting life on earth.

Assertion (A): The earth is the only planet known to support life.

Reason (R): The earth is a terrestrial planet like Mercury and Venus.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true but R does not explain A.

Explanation — Earth supports life mainly because of its liquid water, protective atmosphere, and moderate temperature range. Merely being a terrestrial (rocky) planet, like Mercury and Venus, is not enough, those planets lack the life-supporting conditions that Earth has.

Assertion (A): Earth is a watery planet that supports life.

Reason (R): Distribution of water is responsible for moderating the surface condition of the earth.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — Earth is a watery planet with 71 per cent of the earth's surface being covered by water. Distribution of water moderates the climate and surface condition of the earth, creating ideal conditions for Earth to support life.

Earth has a very hospitable temperature and mix of chemicals that have made life abundant here. Most notably, earth is unique in that most of our planet is covered in liquid water, since the temperature allows liquid water to exist for extended periods of time. Besides liquid water and temperature identify the other features of our planet that make it great for sustaining life?

1. Presence of an atmosphere
2. Solid crust
3. Distance from the sun
4. All of the above.

Answer

All of the above.

Reason — Besides liquid water and temperature, the presence of an atmosphere, a solid crust and an optimum distance from the sun together make the earth suitable for sustaining life. Hence, all of the above features are correct.

............... is a self-regulating and self-sustaining unit of the biosphere?

1. Ecosystem
2. Food cycle
3. Biome
4. Ecology

Answer

Ecosystem

Reason — The self-regulating and self-sustaining structural and functional unit of the biosphere is called the ecosystem. It depends upon the sun for its energy.

Name the cycle through which solar energy moves from non-living to living organisms and back.

1. Carbon cycle
2. Nitrogen cycle
3. Nutrition cycle
4. Energy cycle

Answer

Nutrition cycle

Reason — The nutrition cycle represents the relationship between living and non-living things. Through it, solar energy passes from non-living matter to the producers, then to the consumers and decomposers, and finally back to the environment.

Your teacher is holding a piece of coal and says it contains the basic raw material for life. What does coal comprise?

1. Nitrogen
2. Carbon
3. Oxygen
4. solar energy

Answer

Carbon

Reason — Carbon is the basic raw material of all life, and all living things contain carbon. Coal is a fossil fuel formed from plants and animals buried in the soil, and hence it comprises carbon.

Name the genius Indian mathematician astronomer from the ancient world who was the first proponent of the round shape of the earth.

1. Pythagoras
2. Aryabhatta
3. Brahmagupta
4. Bhaskara

Answer

Aryabhatta

Reason — Aryabhatta, the 5th century Indian mathematician and astronomer, was the first to state that the earth is spherical in shape and rotates on its axis.

You are standing at a beach looking towards the horizon. You hear the horn of a ship. Which part of the ship will you see first?

1. Hull
2. Deck
3. Mast
4. All of them.

Answer

Mast

Reason — While watching an approaching ship from the seashore, we first see only its mast, then the deck, then the funnel, and finally the hull. This happens only because the earth's surface is curved (spherical).

What is the thickness of the Biosphere?

1. 20 km
2. 19 km
3. 15 km
4. 25 km

Answer

15 km

Reason — The biosphere is a thin layer of approximately 15 km, extending from the deepest ocean trench to the highest mountain peak.

How can you prove that the earth is a sphere by looking at the horizon?

Answer

From a high vantage point, the Earth’s horizon always looks circular. As you climb higher, this circular horizon widens and reveals more of the surface. If the Earth were flat, the horizon would stay exactly the same no matter how high you go. This expanding circular view proves the Earth is a sphere.

Briefly describe the shape of the earth. What is the specific name given to it?

Answer

The earth is said to be spherical, but it is not a perfect sphere. The diameter at the equator is greater than the diameter at the poles. The bulge at the equator and compression at the poles gives earth the shape of an oblate spheroid or 'Geoid'.

What is the earth's mean temperature? State its one advantage.

Answer

The mean temperature of the earth is 17 degrees Celsius. This temperature is ideal for life to exist.

Why is the earth called a watery planet?

Answer

Earth is called a watery planet because 71% of the earth's surface is covered by water.

What is 'biosphere'?

Answer

Biosphere is the life zone of the earth. It is that part of the earth's terrestrial system including air, land and water, in which life develops and where life processes in turn get transformed.

Name the conditions necessary for life on earth.

Answer

The conditions necessary for life on earth are as follows:

1. Optimum distance from the sun
2. Ideal temperature of 17 degrees Celsius
3. Presence of Atmosphere
4. Presence of water
5. Presence of lithosphere and biosphere
6. Life-giving cycles operate in nature

Give any two features of the earth that make it a 'Unique Planet'.

Answer

Two features of the earth that make it a 'Unique Planet' are as follows:

1. Presence of Atmosphere
2. Presence of water

What would happen if the average temperature of the earth increased by half a degree?

Answer

If the average temperature of the earth increased by half a degree, it would directly affect the climatic conditions and the ecosystem of the Earth. Species who cannot adapt to these changes would perish.

Trace the cyclical movement of carbon in the three realms of the earth.

Answer

Cyclical Movement of Carbon in the three realms of the Earth

1. Carbon is present in the atmosphere as carbon dioxide (CO₂).

2. Plants absorb CO₂ from the atmosphere during photosynthesis, and convert it into organic matter.

3. When animals eat plants, carbon enters their bodies.

4. Both plants and animals release CO₂ back into the atmosphere during respiration.

5. When plants and animals die and decay, some of the carbon gets stored in the lithosphere as fossil fuels (like coal and petroleum).

6. When these fossil fuels are burnt, CO₂ is released back into the atmosphere.

7. Oceans in the hydrosphere absorb CO₂ from the air. Some marine organisms also use it to form shells.

8. When these organisms die, carbon settles to the ocean floor and becomes part of the marine sediments (lithosphere).

How does the sighting of a ship from the seashore prove that the earth is round in shape?

Answer

While standing at the seashore, watching an approaching ship, we first see only its mast. Then, as it comes closer, we can see the deck in the middle, then its funnel, and finally the hull comes into full view. This can only happen when the earth's surface is curved. Thus, it is proved that the earth is round in shape.

Use a 1m long table to replicate the Bedford Level Experiment. Briefly mention how did you carry out the experiment to prove the shape of the earth.

Answer

Fix three equal-length rods upright on the 1 m table, spacing them about 30 cm apart. Slip a 1 cm-thick folded foil under the centre rod so it stands a little higher, mimicking Earth's curvature. Now crouch at one end and line up your eye with the tops of the two outer rods. The middle rod rises above this line of sight, exactly what the Bedford Level experiment showed, demonstrating that Earth is spherical in shape.

Give a geographical reason for each of the following:
(i) The sunrise and sunset occur at different times at different places.
(ii) The earth is not a perfect sphere.
(iii) Venus is hotter than Mercury.

Answer

(i) The sunrise and sunset occur at different times at different places because the earth rotates from west to east and therefore, people in the east can see the sun earlier than those in the west.

(ii) The earth is not a perfect sphere because the diameter of the earth varies at the equator and at the poles. This difference is due to the centrifugal force of the earth's rotation at a great speed which forms a bulge at the equator and a compression at the poles.

(iii) Venus is hotter than Mercury because Venus is mainly composed of carbon dioxide which produces Greenhouse effect on the surface of Venus. Thus, the temperature on its surface remains very high.

Draw a well labelled diagram to show that the horizon of the earth is circular in shape.

Answer

Describe the role of atmosphere in making earth a habitable planet.

Answer

The atmosphere of the earth is composed of gases like nitrogen (78%), oxygen (21%), carbon dioxide, helium and argon (less than 1%). Atmosphere plays a major role in making earth a habitable planet as-

1. The atmosphere receives heat from the sun by solar radiation and loses heat by earth's radiation. In this way, a balance is maintained.

2. The earth's atmosphere is made up of life-supporting gases like nitrogen, oxygen and carbon dioxide.

3. Ozone present in the earth's atmosphere absorbs harmful ultraviolet rays of the sun.

4. The atmosphere also prevents loss of heat from the earth's surface and helps to keep earth warm.

Describe the role of water in making earth a habitable planet.

Answer

Earth is a watery planet with 70% of the earth's surface being covered by water. Water plays a major role in making earth a habitable planet as-

1. Distribution of water is responsible for moderating the climate and surface condition of the earth.

2. Water bodies like lakes, ponds, rivers etc. are important parts of the ecosystems and biosphere.

3. Water moves in a continuous hydrological cycle. There is a proper balance between evaporation, condensation and precipitation without which life would not be possible.

4. Water bodies help to maintain the temperature of the earth's surface. They rapidly absorb enormous amount of heat during the day, and keep the earth fairly cool. At night, they release the heat absorbed during the day, which along with other atmospheric effects, keep most of the surface from freezing at night.

Describe the role of temperature in making earth a habitable planet.

Answer

Temperature plays a major role in making earth a habitable planet as the earth is the third planet from the sun. It has an average temperature of 17 degrees Celsius which is suitable for life to exist. Other planets of the solar system are either too hot or too cold to support life.

Describe the role of distance from the sun in making earth a habitable planet.

Answer

Distance from the sun plays a major role in making earth a habitable planet as-

1. The earth is at an optimum distance from the sun. Hence, it is neither too hot nor too cold.

2. The distance between the earth and the sun makes life possible on earth. If it was closer to the sun, any life present would get burnt from too much heat of the sun. If it was farther from the sun, life would freeze because of lack of heat.

How does each of the following prove the circular shape of the earth:
(i) Lunar Eclipse
(ii) Pole Star

Answer

(i) Lunar Eclipse

The shadow of the earth on the surface of the moon is clearly visible from earth during lunar eclipse. It appears as an arc of a circle. Since the earth is bigger than the moon, it is rarely oriented in the same position as the moon but the shadow is always circular. This proves the circular shape of the earth.

(ii) Pole Star

The Pole Star can be seen at an angle of 90 degrees at the North Pole. It lies in line with the axis of the earth, and its angle decreases towards the equator. At the equator, the angle is 0 degrees. This can happen only in an arc of a circle. This proves the circular shape of the earth.

What is an ecosystem? Give an example.

Answer

The self-regulating and self-sustaining structural and functional unit of the biosphere is called an ecosystem. This system depends upon the sun for its energy.

For example, Ecosystem of a forest include plants and trees which are eaten by herbivores (deer, rabbit). These animals are eaten by carnivores (lion, tiger). When these animals perish, they are decomposed by decomposers and return to the environment. Again they are consumed by producers and so on.

Give a geographical reason for each of the following:
(i) Earth is a habitable planet.
(ii) From space Earth looks blue.
(iii) Water bodies reduce the day-night temperature variations.

Answer

(i) Earth is a habitable planet as it is covered with green vegetation, enormous blue-green oceans containing over a million islands, a large number of streams and rivers, huge land masses called continents with mountains, ice caps and deserts. It also has ideal temperature for the existence of life.

(ii) From space Earth looks blue because 70% of the earth's surface is covered by water.

(iii) Water bodies reduce the day-night temperature variations as water can absorb enormous amounts of heat without causing much change in its temperature. Water bodies rapidly absorb enormous amount of heat during the day, and keep the earth fairly cool. At night, they release the heat absorbed during the day, which along with other atmospheric effects, keep most of the surface from freezing at night.

Draw a well labelled diagram to show the cyclic circulation of water between the three realms of the earth.

Answer

You have gone from Delhi to Arunachal Pradesh on a study tour with your school during the winter vacation. As you woke up in the morning at 6 o'clock, you noticed the sun has risen whereas at Delhi sun rise is around 7.30 a.m. Similarly around 4.30 it was sunset while sunset is around 6 p.m. in Delhi. What do you think could be the reason for the sun rising and setting earlier than Delhi? Which feature of the earth can you relate to from this?

Answer

The sun rises from the east and sets in the west. Sunrise and sunset occurs at different times at different places because the earth rotates from west to east. Arunachal Pradesh is situated to the east of Delhi and hence, people in Arunachal Pradesh experience the sunrise and sunset earlier as compared to the people who live in Delhi.

This also proves that the earth is geoid in shape as had the earth been flat, the sunrise and sunset would have occurred at the same time all over the world.

The earth depends upon the sun for its energy. Imagine a day, when the sun would not rise. Write down the consequences for the earth and its inhabitants.

Answer

If the sun did not rise for a day, it would have catastrophic consequences for the earth and its inhabitants:

1. The sun is the primary source of energy for all life on earth. The absence of sunlight would cause a rapid drop in temperature, leading to widespread damage to aquatic ecosystems.
2. Without sunlight, photosynthesis will not be possible. The lack of food for plants and herbivores would ultimately lead to the extinction of many species, causing a ripple effect on the food chain.
3. Plants regulate the oxygen and carbon dioxide in the atmosphere. The loss of plants will lead to decrease in oxygen production and affect all living organisms.
4. The sudden and prolonged absence of sunlight would have a profound impact on human society, with panic and chaos as people struggle to adapt to the situation.

Thus, it is clear that the Sun is essential for life on earth.