A «fossil» is the remains or trace of a living thing that lived a very long time ago, gradually turned into stone. When an animal or plant dies and gets quickly covered by layers of mud or sand, these layers protect its body from decaying completely.
Over thousands or millions of years, minerals in the surrounding water replace the body with a rock-like copy that keeps its exact shape — even bones, shells, or dinosaur footprints can turn to stone this way.
Scientists who specialize in this, called «paleontologists», search rock layers for these special stones and study them carefully to learn what ancient living things looked like, what they ate, and how they lived — even though no human ever saw them.
