The fossilization Is a physical-chemical transformation that over the course of hundreds of thousands of years the organism (be it an animal or a plant) is suffering until it becomes a fossil.
Fossilization occurs in exceptional cases, since there must be favorable environmental conditions so that, among others, and especially the absence of oxygen, the main factor of decomposition can occur when an organism dies.
In addition to the process of fossilization requires many years, it is also a process of time and patience, discovering and recovering fossils.
It is called fossil any rest of animal or vegetal origin or the impression that has left some organism that lived on the Earth in geological times very remote and that by diverse causes it did not disintegrate but was conserved (in its totality or some of its Parts) more or less intact, becoming part of the earth's crust.
Thanks to scientific studies, explorations and research carried out by Paleontology, many fossils have been discovered and rescued, although it is considered a minimum percentage of what is supposed to be still in the deepest layers of the Earth.
Tafonomía is the science that studies the dynamics of the fossilization process, provides paleobiological and geological information that helps to understand the characteristics and reasons of conservation of the fossil.
Fossils and their process of transformation can be classified according to various aspects, which are explained below.
Types of fossilization according to the geological process
Permineralization or Petrification
It is the process that occurs when the organism or some of its parts are mineralized, forming a faithful copy on the stone. When dying, many organisms go to the bed of rivers and marshes and are being buried by layers of sediments that, in addition, help to its conservation.
With the passage of time organic matter is being replaced by the surrounding minerals, thus becoming petrified fossils.
It is usually the hardest parts of organisms that mineralize (bones, teeth and shells and animal shells), although petrified fossils of eggs, plants and fruits have also been found.
Inclusion
Inclusion occurs when the organism is trapped within environments or materials that allow its preservation more or less intact until our days. Depending on the conditions, this type of fossilization can be:
- Gelation or freezing : Is given in glacier zone. Throughout history there have been different glaciations in which it is assumed that many specimens of different species died and were buried under large layers of ice that allowed their good state of conservation. In Siberian and Alaska mammals have been found frozen for more than 25,000 years in perfect state of preservation, and can even find food in their digestive system.
- Mummification: The organism is conserved thanks to the dehydration that suffers due to high temperatures.
- Conservation in amber or pitch: In this case the organism is"trapped"by the thick sap of some tree that then solidifies leaving inside the intact organism, even with its soft parts and all its genetic information. This is also the case when the organism is trapped in pitch (crude oil).
Also known as compression or imprint fossilization, it occurs when the organism remains on some surface of relatively little hardness such as sand, mud, silt, clay, limestone, etc., and is then covered by sediments that harden with Time, resulting in a two-dimensional impression of the organism or some part of it.
Types of fossilization according to the chemical process
Carbonation
It happens when the hard parts of the organism are transformed into calcium carbonate or calcite.
Silicification
Silica containing water, sediments or volcanic lava is deposited in the pores and interstices of the organism and facilitates its fossilization.
Piritización
It is when the organic matter is replaced by pyrite or marcasita, product of the combination of the iron present in the water with the hydrogen sulfide that is produced by the decomposition of the organism in an environment without oxygen.
Phosphating
Calcium phosphate present in the bones and teeth of vertebrate animals allows the fossilization with the help of calcium carbonate that possess the rocks and the beds of seas and rivers.
Carbonation
During the Carboniferous period of the Paleozoic Era the earth had great extensions of forests that soon degenerated in coal thanks to particular atmospheric conditions; Is the most common mineralization process for plant species.
Depending on the physical process that occurs
Dislocation
Dismemberment of the skeletons at the level of their joints, due to the destruction of the ligaments.
Fragmentation
Rupture by physical impact or predation of other animals, even before their death.
Abrasion
Deterioration or polishing of the bones, softening their forms and losing details. This can occur over time, external abrasive agents or brittleness in the structure of the skeleton.
Bioerosion
It is produced in marine organisms such as algae or sponges in shallow seas.
Corrosion
The minerals present in the sediments slowly corrode the bones.
According to the presence or not of the organism
Bodily
When the structure of the organism is present and preserved, although transformed to a greater or lesser extent by the mineralization process.
Mold
Print or fill that is left after the organic matter of the organism has disappeared. Depending on whether the fossil reflects the outer or inner part of the organism, the mold will be external or internal.
Fossil substances
When high pressures, high temperatures and physical, chemical and geological changes intervene in what thousands of years ago were living beings, transforming them into liquid hydrocarbons (petroleum), natural gas or coal (graphite, diamonds, calcite, etc.)
CONCLUSIONS
Depending on the type of fossilization, fossils of prehistoric animals (such as dinosaurs), marine species (fish, mollusks and marine arthropods), plants (amber, copal or charcoal) may be found in even ancient hominids and humans.
The term"Living Fossil"can be found in some texts and is the name given to certain species that exist today but are very similar in appearance to species that have already become extinct. It is also used to name specimens believed to be extinct and then found to be alive.
References
- Ma. De los Ángeles Gama Fuertes (2005). Biology 2: multicellular biodiversity. Page 224.
- Patricia Campos-Bedolla et al. (2003). Biology, Volume 1. Page 82-83.
- Fossils. Retrieved from research.us.es
- George Madden (2014). Fossils and types of Fosilization. Retrieved from prezi.com
- Antonia Andrade. Types of fossil preservation. Recovered from uah.es
- Fossil. Recovered from es.wikipedia.org.