Types of Fossilization

Fossils are the remains of either a plant or an animal in its full or fragmented part, which has been preserved by a natural process and discovered later. The knowledge of past plant life has been gathered from the fragmentary fossil remains preserved on stratified rocks. So, the past geological life can be studied by means of fossils. The basis of fossilization depends on the environmental condition in which the process has taken place.

Petrified or Stony Fossils

• In petrified fossils, inorganic mineral substances replace the organic substances of a body's parts, particle by particle in details until only an exact duplication is left. Thus, the original is lost through disintegration, and the resulting fossil retains the external features as such.

Dead and Preserved Bodies

• With this method of fossilization, the actual parts of dead bodies or the whole body of an animal with its original tissues are preserved into ice or chemicals. For example, the delicate parts of insects, crustaceans and spiders are preserved intact in oil shale, tar or amber. Insects are preserved in amber, which is the hardened and fossilized resin from the pine tree. The frozen mammoths recovered from the ice of the Arctic are still fresh.

Natural Molds

• Natural molds of animals are formed through the hardening and subsequent conversion of the surrounding regions encircling the organisms. The enclosed organism disintegrates and is removed by natural process while the surrounding stone forms a cavity that depicts the exact external morphology of the once-enclosed organism. In molds, neither the animal nor its minute details are preserved. Jellyfishes, wings of insects and leaves are preserved in this way.

Casts and Impressions

• Sometimes, the body of an organism has been in mud or clay. The impression of the body hardens and forms a cast. Sometimes, molds are filled with some other materials and a cast is formed. The cast shows the form of the organism but not internal structures. Similarly, cavities of skulls or shells may be filled with hardening sediment or form a natural cast of the contained soft parts.

Fossil of the Whole Body or Entire Fossil

• There are special type of fossils of complete carcasses frozen in the ice off Siberia and Alaska. Thus, the original animals--with parts more or less intact--are preserved, such as mammoths or woolly rhinoceros.

Footprints or Imprints

• An animal walking in partially hardened mud may leave a footprint that becomes preserved.

Unaltered Preservation of Hard Parts

• Hard structures like bones, teeth, shells, etc., are preserved in the geological strata and remain more or less unaltered.