The fossilization of ammonites is possible thanks to silicification
Fossilization is the act and result of becoming fossilized : becoming a fossil . A fossil, meanwhile, is the element of organic origin that, over time, became petrified (that is, turned into stone).
Sediment intervention
When an organism dies, the decomposition of its remains begins. Due to various factors, such as the intervention of animals and bacteria or the action of water, these remains disintegrate; However, this process does not take place if the corpse is quickly covered by sediment.
Underground, the participation of mechanical and biological agents is reduced. Thus fossilization can occur, especially of the hard parts (such as bones ), since the soft parts ( viscera , muscles , etc.) continue to be exposed to microorganisms.
Fossilization begins, in this way, when the soft parts disappear and the spaces that remain are filled with sediments. From then on, various chemical transformations are developed that lead to the replacement of organic elements with minerals .
If it is the remains of an animal, then the soft organic matter becomes a mass very abundant in nutrients, which the bacteria consume. In a case like this, it is common for oil to form. On the other hand, the remains of plant origin give rise to the emergence of humus, which is sometimes transformed into charcoal.
Total mineralization of the remains
If the conditions are favorable, a total change of the molecules occurs in a very long period of time. Fossilization is complete when the remains of the organism are completely mineralized, turning into stone .
Fossils, if well preserved, offer important information about life in past times. Paleontology is the science that is dedicated to analyzing fossil remains to understand the characteristics of the living beings that inhabited our planet a long time ago.
It is important to keep in mind that, regardless of the success of fossilization, if a fossil reaches the surface it will most likely begin to suffer the effects of erosion and be damaged. It can even degrade completely.
Carbonation
This is the name given to the most common fossilization process. The hard parts of the remains are replaced by calcium carbonate in the form of calcite, the most abundant mineral in sedimentary rocks. As an interesting fact, this mineral is also present in the shells of a large number of invertebrates, which increases the presence of this process in nature.
The skeleton of corals is also composed of calcite, something that accelerates fossilization and allows its details to be preserved in an exceptional way. Aragonite is another form in which calcium carbonate can be found in the shells of various mollusks, although it is converted into calcite since its structure provides greater stability .
Silicification
In some cases, the role of the fossilizing agent is assumed by certain chemical solutions that arise from silica, particularly in the form of chalcedony, the most stable and frequent . It is also possible to find siliceous fossils in limestone rocks, something common in echinids, foraminifera, gastropods, brachiopods and ammonites.
Pyritization
If there is no oxygen in the environment, hydrogen sulfide is generated. Its reaction with salts in seawater gives rise to iron sulfides (especially pyrite and brandsite), which replace the organic matter of the skeletons and shells. The fossilization that this process undergoes is characterized by metallic-looking bodies.
Carbonification begins with the accumulation of leaves and trunks without oxygen
Carbonification
In the case of the remains of arthropods whose skeleton is made up of chitin or plants with cellulose, carbonification is the most frequent fossilization process. When leaves and trunks accumulate in an environment without oxygen, humus appears first, and then carbon, until reaching charcoal .
Almost all coal mines arose throughout the terrestrial period known as the Carboniferous , when dense forests abounded on the planet. This fossilization process spanned more than 60 million years .