Curriculum
GRADE VIII SCIENCE
Chapters
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Investigative Science
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Invisible Living World
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Health
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Electricity
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Exploring Forces
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Pressure Cyclones
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Pariculate Matter
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Elements-Compounds-Mixtures
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Solutes-Solvents-Solutions
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Light-Mirrors-Lenses
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Keeping-Time-Skies
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Nature Harmony
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Our-Home-Earth
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Our-Home-Earth
School Revise · Grade 8 · Science · Chapter 13 · Curiosity
Our Home: Earth, A Unique Life Sustaining Planet
Science, Class 8, Curiosity. Of all the worlds we know, only Earth teems with life. This chapter explores what makes Earth able to support life, its four great spheres, and how life keeps going through reproduction.
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What this chapter is about
Why is Earth alive with plants, animals and people when its neighbours are not? In this chapter we learn the conditions that make Earth habitable, the four spheres that work together, and why reproduction keeps life going.
1. What makes Earth able to support life
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The habitable zone Earth orbits the Sun at just the right distance, the habitable or Goldilocks zone, where it is neither too hot nor too cold, so water can stay liquid Earth’s gravity is just enough to hold on to its atmosphere without crushing life. The ozone in the atmosphere blocks harmful ultraviolet rays, and the Earth’s magnetic field shields it from high energy particles from space. In real life: Mars lies outside the comfortable zone and lost most of its air, which is why it is cold, dry and lifeless today. |
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Worked example 1 Question. Why can liquid water exist on Earth but not on planets much nearer or farther from the Sun?
Answer: Because Earth is in the habitable zone, where the temperature keeps water liquid. |
2. The four spheres and the continuity of life
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The four spheres and reproduction the atmosphere (air), hydrosphere (water), geosphere (the solid Earth) and biosphere (all life) interact to sustain life; reproduction, either asexual or sexual, keeps life going from one generation to the next The ozone layer and the magnetic field protect the biosphere, while air, water and land support it. Life continues only because living things reproduce, in asexual reproduction from one parent, or sexual reproduction from two. In real life: A single bacterium splitting in two is asexual reproduction, while a new plant grown from a seed comes from sexual reproduction. |
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Worked example 2 Question. Name the four spheres of the Earth.
Answer: The atmosphere, hydrosphere, geosphere and biosphere. |
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Worked example 3 Question. Why is reproduction important for life on Earth?
Answer: Reproduction produces new individuals, so life continues from one generation to the next. |
Explore with the interactive
Explore it: place Earth in the habitable zone to see where water stays liquid, then tour the four spheres that keep it alive. The interactive opens right here in the lesson.
Practice set A, multiple choice
1. The region around the Sun where water can stay liquid is the …
Habitable, or Goldilocks, zone.
2. Harmful ultraviolet rays from the Sun are blocked by …
The ozone in the atmosphere.
3. The Earth is shielded from high energy particles by its …
Magnetic field.
4. All the living things of the Earth form the …
Biosphere.
Practice set B, short answer
1. Name the four spheres of the Earth.
Atmosphere, hydrosphere, geosphere and biosphere.
2. Give two reasons Earth can support life.
It lies in the habitable zone with liquid water, and its ozone and magnetic field protect life; its gravity also holds the atmosphere.
3. Name the two kinds of reproduction.
Asexual reproduction (one parent) and sexual reproduction (two parents).
Quick summary
| Idea | The idea |
| Habitable zone | right distance for liquid water. |
| Gravity | holds the atmosphere. |
| Ozone | blocks ultraviolet rays. |
| Magnetic field | shields from particles. |
| Four spheres | air, water, solid, life. |
| Reproduction | keeps life going. |
| Open the Virtual Lab |
These free Grade 8 Science revision notes explain why Earth supports life, its spheres, and continuity through reproduction, with clear step by step explanations and detailed labelled diagrams for every student following the new NCERT Curiosity book.
© 2026 School Revise. All rights reserved. This lesson is original content written by School Revise, aligned to the CBSE and NCERT Class 8 Science (Curiosity) syllabus. Unauthorised copying, reproduction or redistribution is not permitted. Curriculum names are used only to indicate alignment.
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