Fossils are lasting impressions of plants and animals that died long ago found in rocks. They can be millions of years old. They can help us study our wildlife evolution and give us insight into the past, including plants and animals that may no longer exist.
How are fossils formed?
- A living thing, such as a plant or animal dies.
- The soft parts of the organism decompose (like skin and guts), they break down until they disappear.
- Often, only hard parts of the organism, such as teeth and bones, will be left. These remaining parts of the animal's body are buried in sediment.
- Layers of sediment continue to build up on top of the remains. This puts a lot of pressure on the first layers of sediment and turns them into a hard rock. This is called sedimentary rock.
- Water seeps through the sedimentary rock, and slowly begins to dissolve the harder parts of the organism. If the hard parts completely dissolve, a space is left. This is called an external mould.
- The water contains lots of minerals. These sometimes enter the mould and form crystals, which makes the remains that are left harden into a fossil. Sometimes, the minerals completely replace the hard parts of the organism and leave a stone cast of what the hard parts looked like.
- Millions of years later, the sedimentary rock rises to the earth's surface, and is worn away by erosion (where wind and water break down the rock.) This leaves the fossil waiting to be discovered by archaeologists or just people casually walking around. Some beaches have excellent places to find fossils.