The four Earth systems
The Earth is not just solid ground. It is made of four large parts called systems that constantly interact. The geosphere is all the rock and soil. The hydrosphere is all the water in oceans, rivers and ice. The atmosphere is the layer of air around the Earth. The biosphere is all living things, from tiny bacteria to giant trees and humans.
These four systems are linked. For example, water from the hydrosphere evaporates into the atmosphere, falls as rain onto the geosphere, and is used by plants and animals in the biosphere. When one system changes, the others are affected too. If we cut down a forest in the biosphere, the soil in the geosphere can be washed away more easily, and the local air in the atmosphere becomes drier. Studying these links helps us understand and protect the planet we live on.
Key idea
The Earth has four systems: geosphere (land), hydrosphere (water), atmosphere (air) and biosphere (living things). They interact all the time.
The layered structure
If we could slice the Earth open, we would see three main layers. The crust is the thin, solid outer layer where we live. The mantle is a thick layer of hot, partly-soft rock below the crust. The core is the centre, made mostly of iron and nickel; its outer part is liquid and its inner part is solid because of the huge pressure.
| Layer | State |
|---|---|
| Crust | Solid, thin |
| Mantle | Hot, semi-solid |
| Core | Liquid outer, solid inner |
Remember
- The crust is the thinnest layer.
- The mantle is the thickest layer.
- The core is the hottest and densest part.