- Fossils are the remains of ancient organisms or evidence of their activity. There are two major types of fossils: body fossils and trace fossils. Body fossils are the remains of the organism preserved in rock or ice. The body fossils show the structure of the organism and form through freezing, petrification and premineralization. Trace fossils display evidence of an organism's activity. Trace fossils include footprints, burrows and coprolites.
- Fossilization is a rare occurrence. Certain conditions need to have been met in order to increase the likelihood of fossilization. First, the organism should have had hard parts that have a high mineral content. Second, the organism should have been buried rapidly, decreasing chances of being eaten by predators or destroyed by aerobic bacteria. Third, the organism should have died in a biologically inert area where sedimentation rapidly occurs. Many fossils are found in ancient deltas or where an ancient sea once was because the remains are covered quickly and are safe from damage.
- Premineralization occurs when hard water infuses the pores and cavities of a deceased organism. When the remains of the organism is exposed to high pressure, the dissolved mineral solidify, creating a fossil. Molds and casts form when shells or other organisms are buried in sediment. These organisms leave an impression or mold in the sediment. If the interior of the shell fills with sediment and then the shell dissolves, it forms a cast or replica of the organism. An impression fossil forms from an imprint on the silt and clay. Plant fossils form by impression. Freezing is an extremely rare form of fossilization where the entire organism is preserved in a block of ice. Coprolites and gastroliths are the indigestible remains of food. Finally, trace fossils indicate the movement of an organism through footprints and burrows.
