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Our Home: Earth, a Unique Life Sustaining Planet – Class 8 Science notes, important questions and MCQs

NCERT Class 8 Science, chapter 13. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Earth is the only known planet with life because it has liquid water, a protective atmosphere, the right temperature and a magnetic field.

What makes Earth special

Right distance from the Sun keeps water liquid (the "habitable zone").
Atmosphere supplies oxygen and carbon dioxide, keeps temperature steady and the ozone layer blocks UV rays.
Magnetic field protects life from harmful solar particles.

Earth's structure and care

Layers: crust, mantle, outer core, inner core.
About 71% of Earth's surface is water, but only a small part is usable fresh water.
Threats: pollution, climate change, loss of biodiversity — reduce, reuse, recycle and save water and energy.

Key terms

Habitable zone: region around a star where liquid water can exist
Crust: thin outermost layer of Earth
Ozone layer: layer of O₃ in the stratosphere that absorbs UV rays

Formulas

Earth's surface ≈ 71% water, 29% land

Important questions with answers

Name the three main layers of the Earth.2 marks

Crust (outermost), mantle (middle) and core (innermost).

Give three features that make Earth suitable for life.3 marks

Liquid water; an atmosphere with oxygen and an ozone layer that blocks harmful UV rays; a suitable temperature range because of its distance from the Sun (also a magnetic field that shields from solar wind).

Explain how human activities are threatening Earth's life-support systems and suggest actions at individual and government levels.5 marks

Burning fossil fuels raises greenhouse gases and causes global warming; deforestation destroys habitats and reduces rainfall; plastic and chemicals pollute soil and oceans; CFCs damaged the ozone layer. Individual actions: save electricity, use public transport or cycle, reduce plastic and recycle, plant trees, save water. Government actions: promote renewable energy (solar, wind), protect forests and wildlife, control industrial pollution, and follow international agreements on climate and the ozone layer.

Quick revision

Water + air + right temperature = life.
Ozone protects from UV.
Save water and energy to protect Earth.

Exam tips

Venus is too hot and Mars too cold for liquid water on the surface.
Most of Earth's fresh water is locked in ice and glaciers.

Practice MCQs

About how much of Earth's surface is covered by water?
1. 29%
2. 50%
3. 71%
4. 90%
Show answer
Answer: (c) 71%. Oceans dominate.
The outermost layer of Earth is the
1. crust
2. core
3. mantle
4. ozone
Show answer
Answer: (a) crust. Crust.
Which gas layer protects us from UV rays?
1. nitrogen
2. ozone
3. carbon dioxide
4. argon
Show answer
Answer: (b) ozone. Ozone.
Earth can have liquid water mainly because of its
1. size only
2. distance from the Sun
3. number of moons
4. colour
Show answer
Answer: (b) distance from the Sun. Habitable zone.
The layer of the atmosphere that protects us from UV rays contains
1. nitrogen
2. argon
3. carbon dioxide
4. ozone
Show answer
Answer: (d) ozone. Ozone layer.
What protects life on Earth from charged particles from the Sun?
1. Earth's magnetic field
2. the ozone layer
3. clouds
4. oceans
Show answer
Answer: (a) Earth's magnetic field. Magnetosphere deflects them.
Most of Earth's fresh water is found in
1. rivers
2. ice caps and glaciers
3. lakes
4. ponds
Show answer
Answer: (b) ice caps and glaciers. Locked as ice.
Earth is in the "habitable zone" because
1. its distance from the Sun allows liquid water
2. it is the largest planet
3. it has many moons
4. it has no atmosphere
Show answer
Answer: (a) its distance from the Sun allows liquid water. Goldilocks zone.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.