NCERT Solutions for Class 8th Science Chapter 13 Our Home: Earth, a Unique Life Sustaining Planet
Updated on 2026-09-19
About this chapter
All life on Earth exists in an astonishingly thin shell. From the highest peak to the deepest ocean trench is only about 20 km against an Earth radius of about 6400 km — if Earth were an apple, the crust would be the apple's skin. Earth lies in the habitable zone (or 'Goldilocks zone'), the range of distances from a star over which water stays liquid . Its nearly circular orbit keeps sunlight and heat steady through the year, so most places escape extreme summers and winters. Earth is also the right size . Its gravity is strong enough to hold on to the atmosphere — Mars's atmosphere is 100 times thinner and Mercury has none — but not so strong that our own weight would crush us. The atmosphere works in three ways: oxygen for respiration, the ozone layer (a three-atom form of oxygen) that b
- Chapter opener
- .1 Why Is Earth a Unique Planet?
- .2 What Do the Planets of Our Solar System Look Like?
- .3.1 Position of the Earth
- .3.2 Size of the Earth
- .3.3 Magnetic field of the Earth
- .4.4 The importance of balance
- .5 What Keeps Life from Disappearing?
- .5.1 Asexual reproduction
- Sexual reproduction in animals
Quick revision
| Term | What it means | Why it matters for life | Where it appears in the chapter |
|---|---|---|---|
| Crust | The thin, solid outer layer of the Earth | Everything alive lives on or just above it — it is as thin, relatively, as an apple's skin | Fig. 13.1, Section 13.1 |
| Habitable zone (Goldilocks zone) | The range of distances from a star over which water stays liquid | Liquid water is, as far as we know, essential for life to evolve | Fig. 13.4, Section 13.3.1 |
| Greenhouse effect | Gases such as carbon dioxide absorb the radiation the Earth gives off after the Sun warms it, so heat does not escape | Mild on Earth, it keeps the planet warm enough for liquid water; runaway on Venus, it makes 450 °C | Fig. 13.2, Section 13.2 |
| Ozone layer | A part of the atmosphere containing ozone, a three-atom oxygen molecule | Acts as a shield that blocks harmful ultraviolet rays which damage living cells | Section 13.3.2 |
| Cosmic rays and solar wind | High-energy particles from deep space and from the Sun | They can damage the atmosphere and reduce the ozone layer; Earth's magnetic field pushes most of them away | Section 13.3.3 |
| Magnetic field of the Earth | The region around the Earth where its magnetism is felt, believed to arise from molten iron moving in the core | A protective shield for the atmosphere, and so for life | Section 13.3.3 |
| Hydrosphere | All the water of the Earth — ponds, lakes, rivers, springs, seas, oceans and groundwater; about 70 per cent of the surface | Water is a good solvent, carries nutrients in plants, regulates body temperature in animals, and is home to millions of species | Section 13.4.1 |
| Geosphere | The solid part of the Earth — rocks, soils and minerals | Supplies nutrients such as nitrogen and potassium, and materials like salt, coal, oil, iron and copper | Section 13.4.2 |
| Geodiversity | The variety of landforms, rocks and soils, together with the processes that shape them | Creates the different habitats in which different kinds of life can thrive | Fig. 13.9, Section 13.4.2 |
| Biosphere | All living beings together with the places where they live — land, water and air | This is where living things interact with their surroundings to survive and grow | Section 13.4.3 |
| Genetic material (genes) | Instructions stored inside every cell that tell it how to develop | They make a calf grow into a cow; small changes in them, passed on, allow adaptation | Section 13.5 |
| Gametes | Specialised reproductive cells carrying only half the parent's genetic material | Half from each parent gives a complete set, so instructions do not double every generation | Section 13.5.2 |
| Vegetative propagation | Asexual reproduction in which a leaf, stem or root planted in soil grows into a new plant | How bamboo, sugarcane, potato, ginger and money plant multiply without seeds | Fig. 13.11, Section 13.5.1 |
| Triple planetary crisis | Climate change, biodiversity loss and pollution taken together | The three biggest environmental challenges now threatening life on Earth | Section 13.6 |
Exercises
- Chapter opener — Probe and ponder Page 210
- .1 Why Is Earth a Unique Planet? — In-text Questions Page 21113
- .1 Why Is Earth a Unique Planet? — Activity 13.1: Let us find out Page 21213
- .2 What Do the Planets of Our Solar System Look Like? — Activity 13.2: Let us find out Page 21313
- .2 What Do the Planets of Our Solar System Look Like? — In-text Questions Page 21313
- .3.1 Position of the Earth — A step further Page 21513
- .3.2 Size of the Earth — In-text Questions Page 21513
- .3.3 Magnetic field of the Earth — In-text Questions Page 21713
- .4.4 The importance of balance — In-text Questions Page 21913
- .5 What Keeps Life from Disappearing? — In-text Questions Page 22013
- .5.1 Asexual reproduction — In-text Questions Page 22113
- .5.1 Asexual reproduction — Activity 13.3: Let us find out Page 22113
- Sexual reproduction in animals — In-text Questions Page 223
- End-of-chapter questions — Keep the curiosity alive Page 226–227
- Science • Society • Interdisciplinary Projects — Discover, design, and debate Page 227