What is a fossil?
A fossil is the preserved remains or trace of a living thing from the distant past, usually more than 10,000 years old. Bones, shells, footprints and leaf imprints can all become fossils.
Most fossils form when a plant or animal is buried quickly in mud, sand or volcanic ash after death. Over long periods, layers of sediment build up and harden into rock. Minerals in groundwater slowly replace the original material, turning bones or shells into stone with the same shape. Soft body parts rarely survive.
Trace fossils, such as footprints, burrows and fossilized dung, show how ancient creatures behaved. Some organisms are preserved almost whole, such as insects trapped in amber or woolly mammoths frozen in permafrost. Scientists who study fossils are called paleontologists.
What fossils tell us
Fossils show how life on Earth has changed over billions of years and help scientists date rock layers. The oldest widely accepted fossils are stromatolites, layered structures built by microbes, about 3.5 billion years old. Fossils of dinosaurs have been found on every continent, including Antarctica.
Did You Know?
Fossil fuels, such as coal, oil and natural gas, formed from the remains of ancient plants and marine organisms buried and heated over millions of years.