Fossils show that organisms have evolved over the years.
A fossil is any evidence of an organism that lived ages ago.
Fossils form in rocks when minerals replace the hard parts of an animal (bones, shell etc.). They show what was on earth millions of years ago, they can also give clues about an organism's habitat and the food it ate.
We also know that the layers of rock where fossils are found were made at different times, this means it's possible to know when a species lived.
Unfortunately very few organisms turn into fossils when they die, so we have gaps in the fossil record.
The fossil record contains many animals that don't exist anymore, they've become extinct. The main reasons for extinction are:
- The environment changing too quickly (e.g. destruction of habitat)
- A new predator or disease kills them all (e.g. humans hunting them)
- They can't compete with another species
An organism's DNA can change…