A fossil is the preserved remains or impressions of a living organism such as a plant, animal, or insect. Some fossils are very old. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants.
The study and interpretation of fossils are called Paleontology and the scientists who study fossils are called Paleontologists.
Studying fossils helps scientists to learn about the past history of life on Earth.
Fossils are found all over the world. Most fossils are found in sedimentary rock such as shale, limestone, and sandstone.
When the minerals replace living material in the dead plant or animal – this is known as petrification. Wood and bone are often petrified, and so are many dinosaur fossils.
When the cell walls in an organism dissolve and are replaced with minerals or the cells' spaces are filled with minerals – this is known as permineralization.
When the organic material becomes encased in mud - this process is known as internment
When plants and animals are trapped in the permafrost – this process is known as refrigeration.
Sometimes, insects or small pieces of plants are found preserved in amber. This happens when animals or plants get trapped in sticky resin from trees, which eventually hardens into amber with the organism (plant or animal) still stuck inside.
There are two main types of fossils:
Fossils can be preserved by several processes.
Petrifaction – When the original material of the organism is replaced with minerals, the fossilization is called petrifaction.
Permineralization – When holes in the organic material are filled with minerals, the fossilization is called pre-mineralization.
Carbonization – Soft tissues can be preserved as carbon films. This process is called carbonization.
Molds and casts – Many fossils are molds or casts.
The fossil record is incomplete for many different reasons:
1. Many organisms live in environments where burial and preservation are unlikely. Fossils are more likely to form when organisms are buried rapidly.
2. Soft-bodies animals without hard parts decay quickly. Fossils are more likely to form from hard parts such as bones, teeth, and shells. Jellyfish and similar organisms are difficult to find fossilized.
3. Weathering and erosion destroy many rocks with fossils.
4. Fossils are found mainly in sedimentary rocks because these rocks form at the earth’s surface where organisms live.
Ichnofossils are traces of ancient life that are not actual organism parts. They include tracks, trails, and burrows.
