Fossils
We know that dinosaurs ruled the Earth for millions of years only because of their fossilised remains. Very few dinosaurs ended up as fossils as it is not very easy to create one.
When living things die there is a chance that their remains will be recorded in stones or rocks. Mostly all living things can create fossils but some are more likely than others to do so.
The soft parts of plants or the skin, muscles and internal organs of animals are unlikely to create fossils as they decay too quickly, but the hard shells of snails and the bones of animals are more likely to become fossilised.
Paleontology
Paleontology is the study of life on Earth using fossil remains. A paleontologist uses the fossilised remains of animals, insects, birds and plants to understand when they lived, how they evolved and how they are related to one another.
How to create a fossil
Most of the fossils found today have been the result of dinosaurs that died near the edge of a river, lake or sea. The soft parts of their bodies would have decayed quickly but the bones and teeth may have been covered by a layer of sand and silt. This layer prevented the rest of the creature rotting away. Over time the sand, mud and silt became hard, trapping the bones inside. The original bones were replaced by minerals while the stronger teeth remained intact. These are known a body fossils.
Sometimes the footprints of dinosaurs became fossilised. Again this was most likely to occur on the shoreline of a lake where the soft sand dried out and was covered by more layers of sand. These footprints give an idea of how the dinosaurs moved. These are known as trace fossils as no body parts have been fossilised.
Insects can be fossilised in amber. This process starts with sticky tree resin that encases part of a plant or insect. The resin hardens and gets covered by sand and dirt. Over millions of years the amber gets encased in stone. Later that stone is mined to find the amber deposits.
Finding Fossils
Over millions of years more and more rock was deposited on top of the fossils and they became compacted and perfectly preserved. But over these millions of years the earth moved and the wind and rain wore the rock away and fossils that were once deep underground started to come back to the surface.