Under the grass and pavements, the whole Earth is made of rock. Not all rock is the same. Some is so hard you can build with it. Some crumbles in your fingers.
Different rocks are different
| Rock | Hard or soft? | Lets water through? |
|---|---|---|
| Granite | Very hard | No |
| Marble | Hard | No |
| Chalk | Soft | Yes, a little |
| Sandstone | Fairly soft | Yes |
Some rocks are permeable — water can soak through the tiny gaps in them, like sandstone. Others are waterproof, so water sits on top and cannot get through, like granite. Hard rocks like granite are chosen for kerbs and buildings because they last.
How soil is made
Soil is not just dirt. It is a mix that takes a very long time to form.
- Wind, rain and ice slowly break rock into tiny pieces. This is called weathering.
- These tiny bits of rock mix with rotting bits of dead plants and animals.
- Together they make soil, which holds water and lets plants grow.
What is a fossil?
A fossil is the shape or remains of an animal or plant that lived a very, very long time ago, now turned to rock. Fossils are how we know about dinosaurs, even though no person ever saw one alive.
How a fossil forms
Put the steps of fossil formation in order (this takes millions of years):
- An animal dies and is buried under mud and sand
- The soft parts rot away but the hard bones stay
- More layers press down and the bones slowly turn to stone
- The rock wears away and someone finds the fossil
A fossil forming is incredibly slow — far longer than a person could ever wait. That is why finding one is so special.