Life lives on a skin as thin as an apple's

This is the last chapter of the book. Time to put together everything you've learnt and ask one big question: why is our home, planet Earth, unlike any other place we know in the universe?

You learnt in Curiosity, Grades 6 and 7, that the Earth is a planet going round the Sun. But it isn't just any planet: it is one that sustains life. It is full of different landscapes, from tall mountains and vast oceans to endless deserts and thick forests.

Satellites let us photograph our own planet. The picture that opens this chapter was taken by an ISRO Earth Observation Satellite. It isn't one photo: nearly 3000 smaller images were joined like the pieces of a puzzle. And it's a false colour image: the real Earth doesn't look like that; scientists add different colours to show different kinds of information. Pictures like this help us study plants on land and tiny organisms in the ocean, and detect ocean temperature, oil spills and wind direction.

So what makes the Earth special? There may be billions of planets in the universe, yet Earth is the only one we know where life exists and thrives in all its forms.

Have you ever wondered where all that life actually is? All the mountains, rivers, forests, animals and people are found in a very thin layer at the planet's surface.

From the tallest mountain to the deepest ocean trench, the crust, where all life exists, is tiny compared with the whole Earth. If the Earth were the size of an apple, the crust would be as thin as the apple's skin. That delicate, life-supporting layer is what makes Earth truly special.

Things we take for granted (Activity 13.1). List features of the Earth that we hardly notice but that really matter. Two are filled in for you:

• the air we breathe doesn't fly off into space, even though (as chapter 7 showed) gas particles move freely and gases have no fixed volume;
• we can stand on the ground, held by gravity (chapter 5), and yet our heart can still pump blood up to our head.

Discuss your own list with your teacher and friends. The Earth gives us the air we breathe, the water we drink, the soil that grows crops, and materials such as rock and timber for homes, buildings and roads.