Fossil Formation

Recrystallization

During metamorphism, the crystals of these minerals may change in composition. -occurs when a solution or precipitate changes the internal physical structure of a fossil. -changes the microstructure of the original minerals; they often reform as larger crystals. The composition of the mineral does not change, only the crystal structure. For example, many shells originally composed of calcium carbonate in the form of the mineral aragonite recrystallize into the more stable form of calcium carbonate called calcite.

Permineralization

One of the processes involved in petrifaction. The fossils created through this process tend to contain a large amount of the original material of the specimen. This process occurs when groundwater containing dissolved minerals (most commonly quartz, calcite, pyrite, siderite (iron carbonate), and apatite (calcium phosphate) ), fills pore spaces and cavities of specimens, particularly bone, shell or wood. The pores of the organisms' tissues are filled when these minerals precipitate out of the water. Two common types of permineralization are silicification and pyritization.

Carbonization

Process of fossilization wherein the original organic material in a fossil has been reduced to a film of carbon looking like a black drawing -the conversion of organic matters like plants and animal dead remains into carbon through destructive distillation. -differs from coalification in that it occurs much faster, due to its reaction rate being faster by many orders of magnitude.

Actual Remains

The body of an organism, with all the parts intact. Usually preserved in ice, amber, or tar. -much rarer than other types of fossils -A good example is mammoth hair, which is often frozen and still preserved.

Casts

These are formed when external molds are filled with sediment.

External Molds

These are imprints of the organism embedded in rocks.

Petrification/Petrifaction/Silicification

These occur when minerals slowly replace the various organic tissues of an organism.

Carbonization/Coalification

These occur when over time all parts of the original organism except the carbon are removed from the fossil over time. The remaining carbon is the same carbon that the organism was made of.

Internal Molds

These occur when sediment fills the shell of a deceased organism such as a bivalve or a gastropod. -These remain after the organism's remains decompose to show the internal features of the organism

Replacement

This occurs when the hard parts of the organism are replaced with minerals over time. -a reaction in which one element replaces another in a compound or when two elements in different compounds trade places - involves the complete removal of original hard parts by solution and deposition of a new mineral in its place. The Petrified Forest in Arizona is an excellent example of this type of preservation. Here the original organic material (wood) has been wholly replaced by silica.

Mummification

This rare form of preservation preserves life form with some tissue or skin intact. -Specimens that are preserved this way are very fragile. -Naturally this usually happens in dry and cold places where preservation happens quickly and effectively. -this is not truly fossilization.

Fossilization in Tar

When organisms become trapped in tar, due to the oxygen deprived environment, it allows for the rapid burial of body parts which are well preserved. A good example is the La Brea tar pits in Los Angeles.

Trace Fossils

provide evidence of the activities of ancient organisms -A type of fossil that provides evidence of the activities of ancient organisms -A type of fossil that is an imprint from organisms without hard parts

Petrification/Petrifaction

the process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals. -Petrified wood typifies this process, but all organisms, from bacteria to vertebrates, can become petrified (although harder, more durable matter such as bone, beaks, and shells survive the process better than softer remains such as muscle tissue, feathers, or skin). -takes place through a combination of two similar processes: permineralization and replacement. These processes create replicas of the original specimen that are similar down to the microscopic level. -the process by which organic matter exposed to minerals over a long period is turned into a stony substance. -The most common mineral to cause petrification is silicon, but other minerals also work. - takes place in porous materials such as bones, plants and shells. The material is buried; later, groundwater percolates through its pore spaces. A solution, commonly supersaturated in either calcium carbonate or silica, precipitates minerals in the spaces. The original wood or shell-like material preserved.

Coalification

the process by which plant remains become coal/the conversion of dead vegetation into coal. -starts with dead plant matter decaying into peat. Then over millions of years, the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon. Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed.

Silicification

the process in which organic matter becomes saturated with silica. A common source of silica is volcanic material. Studies have shown that in this process, most of the original organic matter is destroyed. A common source of silica is volcanic material. -most often occurs in two environments-either the specimen is buried in sediments of deltas and floodplains or organisms are buried in volcanic ash. -water must be present for this to occur because it reduces the amount of oxygen present and therefore reduces the deterioration of the organism by fungi, maintains organism shape, and allows for the transportation and deposition of silica. Also, the geothermic conditions must include a neutral to slightly acidic pH and a temp and pressure similar to shallow-depth sedimentary environments. Under ideal natural conditions, this can occur at rates approaching those seen in artificial petrification. -The process begins when a specimen is permeated with an aqueous silica solution. The cell walls of the specimen are progressively dissolved and silica is deposited into the empty spaces. In wood samples, as the process proceeds, cellulose and lignin, two components of wood, are degraded and replaced with silica. The specimen is transformed into stone (a process called lithification) as water is lost.

Tar Pits/Asphalt Pit/Asphalt Lake

the result of a type of petroleum seep where subterranean bitumen leaks to the surface, creating a large area of natural asphalt.

Fossil Formation

they almost always form in sedimentary rocks. The extreme heat and pressure needed to form igneous or metamorphic rock often destroys or warps the organism. When an organism dies, if the conditions are right, it becomes covered in sediments, which, after being subjected to pressure, becomes rock. This takes a very long time, and the actual organism decomposes by then. A soft organism like a worm or jellyfish usually does not get fossilized because it decomposes too fast. Only the hard parts like skeletons and teeth remain long enough to keep the imprint in the rock while the rock is forming.