What is the process of which fossils form?

Answer 1

To quote wikipedia, the "fossilization processes proceed differently for different kinds of tissues and under different kinds of conditions."

From Wikipedia, there are five types of fossils (http://en.wikipedia.org/wiki/Fossils#Types_of_preservation) -

1. Permineralization

Permineralization occurs after burial, as the empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich groundwater and the minerals precipitate from the groundwater, thus occupying the empty spaces. This process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils. For permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decaying process. The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. This is a form of diagenesis.

2. Casts and moods and melds

In some cases the original remains of the organism have been completely dissolved or otherwise destroyed. When all that is left is an organism-shaped hole in the rock, it is called an external mold. If this hole is later filled with other minerals, it is a cast. An internal mold is formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a bivalve or snail.

3. Replacement and recrystallization

Replacement occurs when the shell, bone or other tissue is replaced with another mineral. In some cases mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material. A shell is said to be recrystallized when the original skeletal minerals are still present but in a different crystal form, as from aragonite to calcite.

4. Compression fossils

Compression fossils, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case the fossil consists of original material, albeit in a geochemically altered state. Often what remains is a carbonaceous film. This chemical change is an expression of diagenesis.

5. Bioimmuration

The star-shaped holes (Catellocaula vallata) in this Upper Ordovician bryozoan represent a soft-bodied organism preserved by bioimmuration in the bryozoan skeleton.[19]Bioimmuration is a type of preservation in which a skeletal organism overgrows or otherwise subsumes another organism, preserving the latter, or an impression of it, within the skeleton.[20] Usually it is a sessile skeletal organism, such as a bryozoan or an oyster, which grows along a substrate, covering other sessile encrusters. Sometimes the bioimmured organism is soft-bodied and is then preserved in negative relief as a kind of external mold. There are also cases where an organism settles on top of a living skeletal organism which grows upwards, preserving the settler in its skeleton. Bioimmuration is known in the fossil record from the Ordovician[21] to the Recent.[22]

fossils form by dead plants or animals from thousands of years ago1. unaltered preservation - (like insects or plant parts trapped in amber, a hardened form of tree sap)

2. permineralization=petrification - (in which rock-like minerals seep in slowly and replace the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil - can preserve hard and soft parts - most bone and wood fossils are permineralized)

3. replacement - (An organism's hard parts dissolve and are replaced by other minerals, like calcite, silica, pyrite, or iron)

4. carbonization=coalification - (in which only the carbon remains in the specimen - other elements, like hydrogen, oxygen, and nitrogen are removed)

5. recrystalization - (hard parts either revert to more stable minerals or small crystals turn into larger crystals)

6. authigenic preservation - (molds and casts of organisms that have been destroyed or dissolved)

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Answer 2

Most follis form when organisms that die become buried in sediments. Sediments are particles of soil and rock. when a river flows into a lake or ocean, the sediments that the river carries settle to the bottom. Layer of sediments may cover the dead organisms. Over millions of years, the layers may harden to become sedimentary rock.

Answer 3

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Answer 4

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