The earth is the only home we have, and everything we use — metal, fuel, food, water — comes out of it. This chapter looks at what the earth is made of and how carefully it has to be used.
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Cut the earth open and you find three layers, getting hotter and denser as you go in.
🧅 The three layers
| Layer | What it is like |
|---|---|
| Crust | the thin solid outer shell we live on — thinnest under the oceans |
| Mantle | thick hot rock below the crust, able to move very slowly |
| Core | the centre, mostly iron and nickel — the hottest part |
Volcanoes and earthquakes happen where the great plates of the crust meet and move against each other. Molten rock below the surface is called magma; once it flows out it is called lava.
🪨 The three kinds of rock
| Rock | How it forms | Example |
|---|---|---|
| Igneous | molten rock cools and hardens | basalt, granite |
| Sedimentary | layers of sediment pressed together | sandstone, limestone |
| Metamorphic | heat and pressure change another rock | marble (from limestone), slate |
A thin skin of soil, a little fresh water and a shell of air — everything alive depends on these three.
Soil takes centuries to form. Rock is broken down slowly by heat, cold, water and roots — this is weathering — and dead plants and animals add humus, the dark part that makes soil fertile. Soil washed or blown away is called erosion, and tree roots are the best defence against it.
💧 Water on earth
| Fact | Figure |
|---|---|
| Of all the earth’s water, the part that is fresh | only about 3% |
| Most of that fresh water is locked in | glaciers and ice caps |
| So the water actually available to us is | a very small share indeed |
Air is about 78% nitrogen and 21% oxygen, with carbon dioxide and other gases making up the rest. Plants need the carbon dioxide; we need the oxygen. Burning fuel adds extra carbon dioxide, which traps heat and warms the earth.
Some resources come back; others are gone once used.
♻️ Two kinds of resource
| Kind | Meaning | Examples |
|---|---|---|
| Renewable | replaced naturally within our lifetime | sunlight, wind, water, forests |
| Non-renewable | took millions of years to form and cannot be replaced | coal, petroleum, natural gas |
Coal and petroleum are fossil fuels. They formed from the remains of plants and animals buried for millions of years. Once burnt they are gone for ever — and they release the carbon dioxide that warms the planet.
Reduce, reuse, recycle — in that order. Reducing what you use is always better than recycling it afterwards, because recycling itself costs energy.
12 questions on the earth, its resources and how to protect them. 🍀
