Our Home: Earth, a Unique Life-Sustaining Planet — Class 8 MCQs with Answers

Our Home: Earth, a Unique Life-Sustaining Planet — important questions & MCQs with answers (Class 8 Science)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Earth is special among the planets because it:

   Ahas no atmosphereBis the largest planetCsupports lifeDis closest to the Sun
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   Answer: supports life

   Explanation: Earth is the only known planet that supports life — a result of its right distance from the Sun, protective atmosphere and liquid water, not its size or closeness to the Sun.

2. Q2 of 6Easy

   The layer of gases surrounding the Earth is the:

   AoceanBcrustCcoreDatmosphere
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   Answer: atmosphere

   Explanation: The atmosphere is the blanket of gases surrounding Earth, distinct from the solid crust, core, or the oceans.

3. Q3 of 6Medium

   The greenhouse effect becomes a problem when:

   Aextra greenhouse gases trap too much heatBthere are no greenhouse gasesCthe Sun goes outDoxygen increases
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   Answer: extra greenhouse gases trap too much heat

   Explanation: The greenhouse effect turns harmful when extra greenhouse gases, beyond the natural balance, trap more heat than the planet needs, pushing temperatures up.

4. Q4 of 6Medium

   The Montreal Protocol (1987) helped by reducing chemicals that:

   Aclean the oceansBwarm the SunCincrease oxygenDdamage the ozone layer
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   Answer: damage the ozone layer

   Explanation: The Montreal Protocol (1987) phased out chlorofluorocarbons and similar chemicals that were breaking down the ozone layer.

5. Q5 of 6Hard

   Which factor is NOT one of the reasons Earth can support life?

   Ait has the most moonsBits right distance from the SunCits atmosphereDits magnetic field
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   Answer: it has the most moons

   Explanation: Earth's habitability comes from its right distance from the Sun, its atmosphere and its magnetic field, not from having the most moons, which plays no role in supporting life.

6. Q6 of 6Hard

   The natural greenhouse effect is beneficial because without it Earth would be:

   Aexactly the sameBtoo hotCmuch too cold for lifeDmade of ice and fire
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   Answer: much too cold for life

   Explanation: Without any greenhouse effect to trap heat, Earth's average temperature would plunge far below freezing, making it much too cold to support life.

Our Home: Earth, a Unique Life-Sustaining Planet notes: key concepts (Class 8 Science)

This closing chapter asks what makes the Earth 'just right' for life. Its distance from the Sun places it in the habitable, or Goldilocks, zone where liquid water — essential for life — can exist. Its size gives it enough gravity to hold an atmosphere of mostly nitrogen and oxygen, whose natural greenhouse effect keeps the planet warm. The ozone layer blocks harmful ultraviolet rays and the magnetic field shields us from harmful particles from the Sun. But human activities — burning fossil fuels, releasing greenhouse gases, polluting and destroying habitats — are causing global warming, climate change and biodiversity loss, so protecting our unique home is urgent.

Earth is unique for life

As far as we know, Earth is the only planet that supports life, thanks to a rare combination of conditions working together.

Right distance and liquid water

Earth lies at the right distance from the Sun for moderate temperatures at which water stays liquid — and liquid water is essential for life.

Habitable (Goldilocks) zone

The region around a star where a planet is 'not too hot and not too cold' for liquid water; Mars lies at the edge of the Sun's habitable zone.

Right size and the atmosphere

Earth is large enough for its gravity to hold on to an atmosphere — the layer of gases around it; a small planet with weak gravity would lose its gases to space.

Atmosphere composition

Air is mostly nitrogen (the most abundant gas) and oxygen (which we breathe), with a small amount of carbon dioxide.

Greenhouse effect

Gases such as carbon dioxide trap some of the Sun's heat, keeping the Earth warm; without this natural greenhouse effect the Earth would be far too cold for life.

Ozone layer

A layer high in the atmosphere that shields the surface by blocking most of the Sun's harmful ultraviolet (UV) rays.

Magnetic field

Generated by movement in Earth's core, it acts like a protective shield against harmful charged particles from the Sun.

Global warming

The gradual rise in Earth's average temperature, caused mainly by extra greenhouse gases from burning fossil fuels like coal and oil.

Climate change

Long-term changes in temperature, rainfall and weather patterns that follow from global warming, with effects such as melting glaciers and rising seas.

Environmental challenges

The major threats today are climate change, biodiversity loss and pollution, largely driven by human activities.

Protecting the planet

Cutting pollution, using clean energy, planting trees and global agreements like the Montreal Protocol (1987) and the Earth Summit (1992) help protect our home.