NCERT Solutions Curiosity Chapter 13 .1 Why Is Earth a Unique Planet? — In-text Questions
Book page 21113 Updated on2026-09-05
Q1.
Have you ever wondered where all life on Earth actually exists?
Answer
All of it lives in an extremely thin layer at the surface — the crust, together with the water on it and the lower part of the air above it.
Highest mountain to deepest ocean trench ≈ 20 km Radius of the Earth ≈ 6400 km So the whole zone of life is about one three-hundredth of the Earth's radius
That is why the book compares it to an apple: if the Earth were an apple, the crust would be no thicker than the apple's skin (Fig. 13.1).
The layers of the Earth. Everything alive — every forest, ocean, city and person — is confined to the green ring at the very edge.
Why it happens: Life needs liquid water, air and sunlight all in the same place. Only the surface has all three: go a few kilometres down and there is no light and no free oxygen; go far up and the air becomes too thin. So life is squeezed into the narrow band where the geosphere, hydrosphere and atmosphere meet.