Geologic Processes of Evolution
Fossils are the remains of organisms, usually hard body parts such as shells and bones, that have mineralized. Bones have basically turned to stone. In order of this process to occur, the organism must have been buried. A classic case of this is in a landslide, which causes the abundant number of fossils found at Burgess Shell.
There are several ways in which fossils are made. In carbonization , the most common fossilization method for plants, organisms are reduced to a thin carbon film. Petrifaction occurs when minerals inside cells are crystallized. Replacement fossilization indicates that the organisms body has been replaced by sulfide or phosphate minerals. Recrystallization is the process where the calcium carbonate of shells turn into calcium calcite, a more stable crystal. Soft-tissue preservation is very rare. In one method of soft-tissue preservation, the plant or animal has been frozen. In another method, mummification, the soft tissues and organs have desiccated, dried out, before they could decay. Organic traps happen when the organism has been trapped, then buried in organic material, such as tree sap, Tar, and Peat Moss.
Note: The definitions on the following pages were taken from Microsoft ® Encarta Encyclopedia.