Live Science explains that fossilization can occur in a number of ways, the most common of which is called petrification. Once the soft organic tissues such as skin and muscle decay, the bones and other hard parts remain intact. As water covers the remains, minerals dissolved in the water seep into the bones, causing crystallization and preservation.Continue Reading
Carbonization is another common method of fossil creation and is often seen as an impression in sedimentary rock. This process occurs when the heat and pressure from a buried organism causes the release of available oxygen and hydrogen in the tissues, leaving behind a tell-tale carbon residue on the rock around it.
Another less common method of fossilization is the encasement and preservation of an entire organism, soft tissues and bones alike. This type of fossil results from a sudden encasement in tar or resin or the quick freezing of an animal, such as a woolly mammoth.
Finally, a fossil can be formed as a mold or cast. This method involves the complete decomposition of an organism in sedimentary rock, leaving behind a hollow cavity of its exterior form. If this area becomes filled with other minerals, a cast of the original shape can be left behind.Learn more about Geology