GeographyICSE Class 9 · Earth as a Planet

Shape of the Earth and Conditions That Support Life (ICSE Class 9 Geography)

Updated 17 October 2026 · Draft, not yet fact-checked

The earth is the third planet from the sun and is shaped like a geoid: slightly flattened at the poles and bulging at the equator. Evidence of its roundness includes the disappearance of ships hull first, the circular shadow in lunar eclipses and photographs from space. It supports life because of a moderate temperature, liquid water and an atmosphere with oxygen and an ozone shield.

Notice the earth is a little flatter at the poles than a perfect sphere, and the curved sea hides a departing ship's hull before its sail.

Illustration drawn for QuestionBuddy.

Understand Shape of the Earth and Conditions That Support Life

1. The earth in the solar system. The earth is the third planet from the sun, after Mercury and Venus, and the fifth largest. It is the only planet known to support life. The sun is a star at the centre of the solar system; the earth is about 150 million km from it (a rounded figure) and takes about 8 minutes for sunlight to reach it.

2. A geoid. The earth is not a perfect sphere: it is slightly flattened at the poles and bulges at the equator because of rotation. Its equatorial diameter is a little larger than the polar diameter (about 12,756 km and 12,714 km, rounded). This shape is called a *geoid* ("earth-like").

3. Evidence that the earth is round.

A ship's hull disappears from view first and then the funnel as it sails away; on returning, the funnel is seen first and the hull later.
The shadow of the earth on the moon in a lunar eclipse is always curved.
A circumnavigation (travelling east or west, one returns to the start).
Photographs from satellites and astronauts show a curved globe.
Time differs between places as the sun rises earlier in the east.
The horizon is circular, and widens as one climbs higher.

4. Conditions that support life.

*Distance from the sun*: neither too hot nor too cold; average temperature allows liquid water.
*Water*: about 71 per cent of the surface; the hydrosphere supports all life.
*Atmosphere*: contains oxygen for breathing, carbon dioxide for photosynthesis, and traps heat.
*Ozone layer*: absorbs harmful ultraviolet rays.
*Gravity* of suitable strength holds the atmosphere.
*Rotation* prevents extreme day-night temperatures.

Shape of the Earth and Conditions That Support Life: key facts

Shape: Geoid
Flattened at poles
Bulges at equator
Dimensions: Equatorial diameter about 12,756 km
Polar diameter about 12,714 km
Distance from sun about 150 million km
Proofs: Ship hull first
Curved eclipse shadow
Circumnavigation
Satellite photographs
Life: Right temperature
Liquid water
Oxygen
Ozone layer
Gravity

Shape of the Earth and Conditions That Support Life in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Watching a ship

Suppose a student on a beach watches a ship leave the harbour and sees its lower part disappear before the mast.

What does this show?

Try it first, then show the solutionSolution

If the earth were flat, the whole ship would shrink evenly.
The curved surface hides the hull first.

Answer: It shows the earth is curved.

Memory hook: Hull goes first.

Tricks to remember Shape of the Earth and Conditions That Support Life

Short memory aids. Say each one aloud once, then use it on a question the same day.

Geo-id
Geoid: earth-like, not a perfect sphere.
Use it when: Shape of the earth.
T-W-A
Temperature, Water, Atmosphere.
Use it when: Conditions for life.

Shape of the Earth and Conditions That Support Life: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Name the shape · 2 marks · Short answerBoard level

What is the shape of the earth called and why is it not a perfect sphere? [2]

Try it first, then show the solutionSolution

Geoid.
Rotation makes it flat at the poles and bulging at the equator.

Answer: Geoid; flattened at poles and bulging at equator due to rotation.

Example 2: Proof from eclipse · 3 marks · Short answerHarder board level

How does the shadow of the earth on the moon prove that the earth is round? [3]

Try it first, then show the solutionSolution

In a lunar eclipse the earth lies between sun and moon.
The shadow on the moon is always circular or curved.
Only a round body always casts a curved shadow, whatever its position.

Answer: The shadow in every lunar eclipse is curved, which only a round earth can cast.

Example 3: Planet comparison · 3 marks · Short answerHarder board level

Venus is nearer to the sun and Mars is farther. Explain how distance from the sun affects the chance of life. [3]

Try it first, then show the solutionSolution

Nearer planets are too hot and farther ones too cold.
Water would boil or freeze.
Earth lies at a distance where liquid water exists.

Answer: The earth is at a distance that keeps temperatures suitable for liquid water.

Example 4: Water and temperature · 4 marks · Long answerHarder board level

Explain how the oceans help to keep the earth habitable. [4]

Try it first, then show the solutionSolution

Water has a high heat capacity, so oceans warm and cool slowly.
Ocean currents carry heat from warm to cool areas.
Water evaporates and forms rain for land.
Oceans provide habitats and dissolve gases.

Answer: Oceans moderate temperature, supply rain and provide habitats.

Example 5: Case: the rocket · 6 marks · Case-basedHOTS / competency

Case. An astronaut orbiting the earth sees a bright blue globe with a thin glowing blanket round it. (i) Name the blanket. [1] (ii) Two functions that help life. [2] (iii) Why does the globe appear blue? [1] (iv) Why would an earth without this blanket be unsuitable? [2]

Try it first, then show the solutionSolution

(i) Atmosphere.
(ii) Supplies oxygen and traps heat; also filters ultraviolet rays.
(iii) The oceans cover most of the surface.
(iv) Temperatures would be extreme and there would be no oxygen.

Answer: (i) Atmosphere (ii) Oxygen and heat trapping (iii) Large water cover (iv) Extreme temperatures and no breathable air.

Where students lose marks in Shape of the Earth and Conditions That Support Life

The slips examiners see most often, and what to write instead.

Mistake: Calling the earth a perfect sphere
Flattening ignored.
Do this: Use the term geoid.
Usually costs: 1 mark.
Mistake: Writing one proof only
One argument for a 3-mark question.
Do this: Write at least two proofs with brief explanations.
Usually costs: 1 mark.
Mistake: Confusing planet and star
Sun is a star.
Do this: The earth is a planet, the sun a star.
Usually costs: 1 mark.

Exam tips

Give two or three proofs with explanation.
Use the word geoid.
For life conditions, link each condition to its effect.
Draw a small diagram of the ship disappearing.

Practice questions on Shape of the Earth and Conditions That Support Life

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which planet is third from the sun?
(a) Venus
(b) Earth
(c) Mars
(d) Mercury
Hint
Order.
Answer
(b) Earth.
Q2 · 2 marks · Very short answerBoard level
Name two proofs of the earth being round. [2]
Hint
Ship.
Answer
The hull-first disappearance of ships and the curved shadow in a lunar eclipse.
Q3 · 1 mark · Very short answerBoard level
About what share of the earth's surface is covered by oceans and seas? [1]
Hint
Blue planet.
Answer
About 71 per cent.
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Mountains do not prove the earth is not round.
Reason (R): Their height is tiny compared with the earth's size.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Scale.
Answer
(a).
Q5 · 2 marks · Very short answerBoard level
Why is the earth called a geoid and not a sphere? [2]
Hint
Flattened.
Answer
Because it is slightly flattened at the poles and bulges at the equator.
Q6 · 3 marks · Short answerHarder board level
Explain why the ozone layer is essential for life on land. [3]
Hint
UV.
Answer
It absorbs harmful ultraviolet rays that cause skin damage and harm living cells.
Q7 · 3 marks · Short answerHarder board level
Suppose the earth were twice as close to the sun. Predict two consequences. [3]
Hint
Hotter.
Answer
Higher temperatures would evaporate oceans, and living things would not survive.
Q8 · 3 marks · Short answerHarder board level
Distinguish between the equatorial and polar diameters and state which is larger, with reason. [3]
Hint
Rotation.
Answer
The equatorial diameter is larger because rotation causes a bulge at the equator.
Q9 · 3 marks · Long answerHOTS / competency
Case. A student says that because the horizon looks flat from the beach, the earth must be flat. Rebut her with two arguments. [3]
Hint
Scale.
Answer
The earth is huge, so a small part looks flat; moreover a ship disappears hull first and the horizon extends farther when viewed from a height.
Q10 · 4 marks · Case-basedHOTS / competency
Case. A new planet has water, but its sky is full of carbon dioxide with no oxygen and no ozone. (i) Could humans live there? [1] (ii) Give two reasons. [2] (iii) What else must be checked? [1]
Hint
Atmosphere.
Answer
(i) No. (ii) No oxygen to breathe and no ozone to block UV. (iii) Temperature and gravity.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Shape of the earth?Show answer
Geoid.
2.Earth is which planet from the sun?Show answer
Third.
3.Percentage of water?Show answer
About 71.
4.Layer absorbing UV?Show answer
Ozone layer.
5.Why is the earth flattened at the poles?Show answer
Rotation.

Shape of the Earth and Conditions That Support Life: frequently asked questions

Is the earth perfectly round?

No, it is a geoid.

Why is the earth called the blue planet?

Because most of its surface is water.

Do other planets have life?

None is known so far.