More from this author. 1  Largest World Cities: 2014. 2  World Urban Areas Population and Density: A 2012 Update. 3  Largest Cities in the World: 2016. 4  Largest 1,000 Cities on Earth: World Urban Areas: 2015 Edition. 5  The Costs of Smart Growth Revisited: A 40 Year Perspective.
Definition of fossil. 1  1 : a remnant, impression, or trace of an organism of past geologic ages that has been preserved in the earth's crust â compare living fossil. 2  2a : a person whose views are outmoded : fogyb : something (such as a theory) that has become rigidly fixed.
Fossils are imprints left during the decay of a plant or animal. They are buried within sediments that are not disturbed for long periods. Mud is often a medium for fossil development since is can become shale or limestone over time.The study of various types of fossils have allowed us to learn about the structure and behavior of life many thousands of years ago.rue-form fossils are body parts of an animal or remains of a substance. They are often formed when the organism is caught in ice, tree sap or tar. Complete features are left behind.