The geochronology it is the science that determines the chronological periods of geological events that have occurred in the course of Earth's history. In addition, it is in charge of establishing the geochronological units, which are divisions used to form the geological time scale..
Geochronology should not be confused with biostratigraphy, which is dedicated to the chronological order of sediments through fossil content. The difference is due to the fact that biostratigraphy, on the contrary to geochronology, cannot provide the absolute ages of the rocks, but rather places them within a time interval where certain fossils have existed..
Some researchers consider that geochronology is an essential discipline within any geological, paleontological and / or geological study. However, it is a science that is currently only taught in certain master's degrees that specialize in archeology and human evolution..
Likewise, geochronology can be studied as a complement to other scientific and humanistic disciplines, such as chemistry, physics, biology, history, archeology and anthropology..
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The word "geochronology" consists of a recently created neologism and comes from three Greek words: geo -relative to land-, chronos - which means "time" - and lodge, coming in turn from logos -word, study or thought. Therefore, geochronology can be translated textually as: "The study on the time of the age of the Earth".
The term as such arose at the end of the 19th century, specifically in 1893 and its appearance took place after the emergence of stratigraphy, since both disciplines are closely linked. While stratigraphy describes the rocky or sedimentary strata, geochronology can answer how old these findings are..
Since ancient times, man has tried to determine the age of formation of the planet. For example, some Hindu philosophers considered that everything that exists is part of a cycle, which encompasses the process of creation, life and death of the Universe..
Therefore, for these thinkers, a cycle of the Universe was equivalent to one day of the life of the God Brahma, that is, approximately 4300 million years. According to these postulates, the Earth would currently be about 2 billion years away from restarting this cycle..
Later, two Greek philosophers were interested in the age of the Earth, these being Xenons of Colophon (570-470 BC) and Herodotus (484-425 BC). The first recognized that the fossils were remnants of a more primitive type of life, deducing that the rocks had originated from sediments at the bottom of the sea.
As for Herodotus, this philosopher during his travels noticed that the Nile left in its avenues a series of layers of sediment that, in order to form, many years had to pass.
Starting in the seventeenth century, a series of studies based on the observations of naturalists began to be carried out. This made it possible to accumulate data and begin to consider the Earth as a planet that could not have been created in a single instant..
This means that in the seventeenth century it was established that the Earth was formed over many millions of years, and not in a single moment of creation..
Among the most important naturalists, Nicolás Steno (1638-1686) stood out, who in 1667 managed to affirm that the fossils were the evidence of the existence of other more primitive times.
In addition, in 1669 he made the first attempt at dating the rocks through his law of superposition of the strata, which recognized that the rocks above were younger than those below..
Another scientist interested in dating the age of the planet was Robert Hooke (1637-1703), who managed to recognize that fossils suggested recurring changes in the Earth throughout its history, since many mountains had been transformed into sea and vice versa..
In 1910, Gerard de Geer (1858-1943) implemented the varve method, which consists of studying the thin annual layers of clay that are included in glaciers - called varves -, allowing him to identify sediments from 13000 BC. C.
Currently, a method called obsidian hydration is also used, which is based on measuring the elapsed time of the creation of an obsidian surface, taking into account the hydration or alteration fence.
Geochronology studies the absolute age not only of rocks, but also of sediments and minerals. However, the statement of an age or geological period always has a certain level of uncertainty, since there may be variations depending on the methods used by the discipline..
To carry out its studies, geochronology uses radiometric dating, which consists of a technique that allows dating rocky and organic materials through the comparison of a radionuclide -atom with excess nuclear energy- with the decomposition products, which are develop through a known decay rate.
Geochronology also uses thermoluminescence dating, which is a method also used by archeology to determine the age of certain elements that have been subjected to heating. This is achieved through a series of alterations that cause ionizing radiation in the structure of minerals..
One of the most recognized investigations in the field of geochronology was carried out by Morán Zenteno and Bárbara Martiny, entitled Geochronology and geochemical characteristics of the tertiary magmatic rocks of the Sierra Madre del Sur (2000).
In this work, the scientists described the ages of the tectonic environment of the southern part of Mexico, taking into account the condition of the deformation of the crust in that area..
In summary, the research established that the magmatic rocks of the Sierra Madre del Sur range from the Paleocene to the Miocene, distributed in an area that contains basements of petrological nature..
Another very important investigation for this discipline was carried out by César Casquet and María del Carmen Galindo, whose work was titled Metamorphism in the Cameros Basin. Geochronology and tectonic implications (1992).
These scientists dedicated themselves to describing the geological phenomena of the Sierra de los Cameros, which showed an interesting case due to its metamorphic conditions, which occurred as part of the tectono-sedimentary evolution of the region..
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