What is a Fossil?
The word fossil original was used to describe anything that was dug up from the ground. The meaning has changed over time and today a fossil is any evidence of ancient life.
Ancient is considered to be older than 10,000 years, but there is some gray area. For instance 4,000-year-old mammoth bones from Wrangle Island of Russia are considered fossils by many paleontologists, while 4,000 year old mummified cats in an ancient Egyptian pyramid are not considered fossils. Therefore fossils are any evidence of life generally older than 10,000 years old.
Commonly the hard parts of animals and plant are preserved as fossils. These include bone, teeth, shell, and wood. Many people think a fossil must be made of stone or be petrified. This is not the case. Preservation is not a criterion for determining what a fossil is. A fossil bone or shell may be the original material preserved or minerals in one of may replace the original material, or the fossil may be an impression of the bone or shell.
In rare instances soft-tissue of an animal or plant or even the whole animal may be preserved as a fossil. Examples of these fossils include impressions of soft-bodied animals, or thin carbon impressions of plant leaves, or pollen grains buried in lake sediments, or insects trapped in amber, or frozen tissue and bones of mammoths found in arctic ice.
Fossils do not have to be a part of an animal or plant. Fossils may be evidence of the activities of animals or plants including burrows, tracks, trails and footprints. Fungi, protozoan, and bacteria can be fossils. Even traces of chemicals that can only be generated by life are considered fossils. Any evidence of ancient life is a fossil.
Most fossils are from the hard parts of animals and plants. This includes bone, teeth, shell and wood. Impressions and molds of shells and bones are also fossils. As are thin carbon impressions of plant leaves or insects trapped in amber, pollen grains in buried lake sediments or frozen tissue of mammoths found in arctic ice. Burrows, tracks, and footprints preserved in stone. Insect traces preserved in fossil leaves. Even traces of chemicals that can only be generated by life are considered fossils.
Fossils may be the original bone or shell material or the bone and shell maybe replaced by rock/minerals a process called mineralization. Petrified is a poor word that is often used to describe fossils i.e. petrified wood. It should be called permineralized wood or mineralized wood.