subject: How Are Fossils Formed? [print this page] Here are some of the most common ways that fossils are formed:
1. Freezing. Freezing provides the most complete preservation, but it is also occurs very rarely. Temperatures must be low enough to prevent any decay and must stay that way for a sustained period of time. Remains of wooly mammoths and other ice age animals discovered in Siberia are among the rare examples of fossils preserved by freezing.
2.Desiccation. Mummies, pressed leaves, dried flowers and fossils discovered in desert areas are common examples of this type of preservation. When all moisture is removed from remains of a dead animal or plant it is more likely to survive over time, although the removal of this moisture leaves the item extremely fragile.
3.Perimineralization. In this process, minerals like iron, calcite and silica fill in the microscopic gaps in the remains of animal or plant. Over time, the softer portions of the remains decay and disappear but the mineral shell remains. Perimineralization occurs only if the remains are buried and then immersed in mineral-rich water. Minerals can fill in very small spaces and result in fossils like petrified wood or rock-hard replicas of the original species.
This type of preservation can result in beautiful specimens. Many examples are available at local museums and everyday uses can range from furniture pieces to fossil jewelry.
4.Casts and molds follow a similar process. A living animal can leave footprints or the remains of plants or animals may leave an impression in mud. The mud is exposed to enough minerals that the casting hardens and is preserved.
5.Amber and tar also make effective preservatives. Insects who become trapped in tree sap can, in some cases, resurface as preserved amber fossils many centuries later. Tar pits, like the one in La Brea often catch both predators and prey and preserve the skeletons and other hard portions of their bodies.
