Fossils are the remains of living organisms, either plants or animals, that have been preserved. Below you will find out more about how they are preserved and the different types of fossils there are. Fossils allow us to see how Earth used to be – was it covered in oceans? was there oxygen? what kind on animals dominated?. They are important because they can be the only evidence that certain animals and lifeforms existed. Palaeontologists, geologists who study fossils, are able to find out things such as the order of rocks, the ages of rocks, the evolution of Earth and its animals such as humans, and how the concentration of gasses in our atmosphere, such as oxygen and carbon dioxide has changed over time.