Introduction
A fossil is any substance that evidences a once-living organism (University of Arizona, 2016). As such, fossils evidence the ancient life forms which inhabited the earth long time ago and were preserved by a natural process. Most of the fossils are found in sedimentary rocks formed from the sediments of rivers, seas, and lakes. Some of these fossils are actual remains of living things such as bones, or events that happened in the past, for instance, the dinosaur footprints. However, it is ordinarily the hard parts of organisms that get preserved under the right conditions and the interaction of several factors. This paper describes the fossilization process, the fossilization processes, and the exceptional preservation of some fossils.
Fossilization Process
Fossilization is a rare process that happens only when an animal or a plant dies in the right circumstances (BBC, 2016). After death, bodies of both animals and plants are usually decomposed by bacteria and other elements. Moreover, body parts such as bones get smashed through erosion and corrosion. Such elements cannot allow fossilization to take place. Fossilization occurs when, plants and corpses get buried in sand or soil that is free of the above decomposing elements (BBC, 2016). Such places include the sea bed or river bed. As time moves on, the buried remains are buried deeper and deeper, the mud is compressed and starts to form a stone. Moreover, as times passes on, chemicals and minerals percolate through the sediment and result in the gradual crystallization of the remains (BBC, 2016). However, BBC (2016) notes that some of the crystalized remain my dissolve leaving a hollow. In cases like this, paleontologists use liquid rubber to make a cast or use a scanner to reshape the original remain. Also, the fossilization process may entail minerals from rocks gradually impregnating the bones, shells, or wood, thereby changing its chemical composition (BBC, 2016). This allows the remains to survive as long as the rock enclosing it. Rocks too have a limited lifespan. When the rocks enclosing the crystallized remains finally erodes away, the fossil is revealed to the surface of the ground where it may be luckily noted and collected by a fossil collector. As stated earlier, there are conditions necessary for fossilization to take place. There are several processes responsible for fossilization to take place. They include unaltered hard parts, mold, carbonization, permineralization, replacement, and recrystallization.
Fossilization Processes
Unaltered hard parts
This happens when an organism’s hard parts, which are composed of minerals such as calcite, aragonite, silica, and chitin, are preserved intact devoid of chemical alterations to the original mineralogy (University of Arizona, 2016). However, this process is rare for old fossils, and is only common with young fossils.
Mold or casts
A mold happens when the fossil enclosed inside a sediment dissolves leaving a void that takes the shape of the dissolved material (University of Arizona, 2016). The impression left of the skeletal material is called a mold. As mentioned earlier, paleontologists can use the molds or casts to reconstitute the original form of the skeletal material through the use of liquid rubber or scanning.
Carbonization
This process entails a chemical reaction. It occurs when after the distillation of all organic volatiles as a result of heat and/or pressure, the liquid or gaseous contents of are forced out leaving a thin film of carbon remnant of the organism (Marlowe, 2014). Coal mines are examples of carbonized fuels. Carbonization process is easily recognized by the shiny black or dark brown color (University of Arizona, 2016).
Permineralization
This process is also called petrification. In this process, skeletal materials such as shells, teeth, and bones are seen as having porous internal structures. These pores allow in foreign materials from the soil and groundwater, and the chemical composition of the original hard parts of the organism are altered in some way (Marlowe, 2014). I such a scenario happens, the fossil is said to have been permineralized. Most wood fossils such as petrified wood are permineralized silica.
Recrystallization
This process is perhaps, according to University of Arizona (2016), the most difficult to recognize and understand. Recrystallization happens when a solution or a precipitate alters the internal physical form of a fossil in terms of size and/or geometry over a period (Marlowe, 2014). However, despite the change on in size and/or geometry, the chemical composition remains unaltered. An example of such a process is the aragonite recrystallization to calcite (University of Arizona, 2016).
Replacement
As the name suggests, this process entails the replacement, molecule by molecule, of the skeletal material with a completely new and foreign material over a long period (University of Arizona, 2016). The original mineralogy dissolves giving way to a new mineral precipitates. Such processes include silification, where silica replaces carbonate, and pyritization, where calcium carbonate is replaced by pyrite (University of Arizona, 2016).
Exceptional Preservation
Most living organisms are never preserved, and only a small number of organisms get preserved as fossils. Fossilization mainly happens due to the presence of hard parts in animals and plants such as the shell, bone, teeth and wood (BBC, 2016). However, on rare occasions, some soft parts are also preserved through particular conditions. For instance, such features as the original skin color, muscle fibers, skin texture, and feathers are preserved. These fossil deposited are called lagerstatten, and encompass soft tissues of ancient creatures in fine details. Such discoveries allow for a better reconstruction of an organism hitherto known from skeletons or carapaces. They allow researchers to understand and reconstruct ancient life and environments as they offer finer records of ancient biodiversity and behavior (University of Arizona, 2016). Exceptional preservation could only be possible in an anoxic environment where decomposing elements and erosion activities were minimal or non-existent (University of Arizona, 2016).
Conclusion
Fossils are instrumental in the reconstruction of ancient biodiversity and the understanding of the history of the earth. As such, the fossilization process is of great importance to paleontologists in their quest to understand the history of the earth. The process of fossil formation begins with the death of the organism, after which several processes result in various categories of fossils. These processes include unaltered hard parts, molds or casts, carbonization, permineralization, and recrystallization. Fossilization usually involves the hard parts of an organism such as bones and wood. However, on rare occasion, exceptional preservation occurs. This entails the conservation of soft parts such as skin texture and color, muscle fibers, and feathers. This process is possible in particulr conditions where decomposition agents are minimal or non-existent. Exceptional preservation is important in the better reconstruction of ancient life. .
References
BBC. (2016). Fossils. Retrieved from Nature and Prehostoric Life: http://www.bbc.co.uk/nature/fossils
Marlowe, S. (2014). Type Of Fossils. Retrieved from Pangea Institute: http://www.pangeainstitute.us/resources/fossiltypes.pdf
Uviversity of Arizona. (2016). Fossilization and Preservation. Retrieved from The Uviversity of Arizona-Department of Geosciences: http://www.geo.arizona.edu/geo3xx/geo308/FoldersOnServer/2004%20LABS/Lab%201%20-%20fossil&taph&ichno.pdf
