How are geological epochs determined

Vulkane.net

Geological timescale and geological ages

Geological processes usually take place so slowly that we humans hardly notice them. Great changes require most millennia, or even millions of years. Therefore, a special geological time scale is used in the history of the earth. This scale is divided hierarchically. This hierarchy is based on rock layers and tectonic events, each of which is assigned to a specific time period.
The rocks see themselves as a window into the history of the earth or its archive in which geoscientists read. Fossils that are found in sedimentary rock layers serve the scientists as time stamps to identify the rock layers worldwide. So different levels of the hierarchical time scale are assigned to a certain evolutionary development step. By means of this biostratigraphy, very fine division of the time scale is possible. Stratigraphy connects different rock layers with one another. In addition to sedimentary rock layers, volcanic deposits can also be stratigraphically differentiated and correlated. For a long time, these methods were the equipment of geoscientists to determine the approximate age of a rock layer and to read it in the earth archive. Nowadays, the most modern radiometric methods for determining the time of the rocks are available to the scientists and can thus assign them to an absolute age.

To classify the nearly 4.6 billion years of the earth's history in a meaningful way is very complex. This requires several levels that are arranged parallel and horizontally. There are different nomenclatures that have now been standardized by an international commission (ICS). However, two concepts exist side by side: that of geochronology and chronostratigraphy. They differ in the nomenclature by the naming of the hierarchy levels, whereby the names of the intervals are identical in both concepts. Here is the geochronology:

  • Aeoneon)
  • Era & nbsp (English & nbspera)
  • Period & nbsp (English & nbspperiod)
  • Epoch & nbsp (English & nbspepoch)
  • Age & nbsp (English & nbspage)

    The names of the chronostratigraphic hierarchy levels are:

  • Aeonothemeonothem)
  • Archery topic (English & nbsperathem)
  • System & nbsp (English & nbspsystem)
  • Series & nbsp (English & nbspseries)
  • Level & nbsp (English & nbspstage)

    For most of the earth's history, our planet has been lifeless. Due to the earth's dynamics and the rock cycle, very few rocks have survived from this time. The knowledge from this period, which we call the Precambrian, is correspondingly incomplete. The Precambrian is the longest aeonothem (aeon) and spans the unimaginable period of 4,059 million years. It is divided into 3 aera themes (era): Hadaic, Archaic, Proterozoic. The latter covers a period of more than 2 billion years and is divided into: Paleoproterozoic, Mesoproterozoic and Neoproterozoic. These systems (periods) are in turn divided into series (epochs). The Neoproterozoic is divided into: Tonium, Cryogenium, Ediacarium, which in turn can be divided and cover very specific periods of time. The entire hierarchy functions according to this scheme.

    The most famous geological ages are most likely Devonian, Jurassic, Cretaceous and Eocene. Most coal deposits were formed during the Devonian and the Jurassic was the age of the dinosaurs, which became extinct at the end of the Cretaceous. Most mammal species evolved in the Eocene. The direct ancestors of humans only entered the history of the earth a good 7 million years ago during the Neogene. Man, on the other hand, is a Quaternary child. These two systems belong to the arena of the Cenozoic, the modern earth era.

    Most of the volcanoes mentioned on vulkane.net were formed during the Quaternary. Only rarely are older volcanic systems preserved or their deposits exposed. The Quaternary began 2.588 million years ago and continues to this day. It is divided into further series and levels which are shown in the graphic on the left. (Sources: Wikipedia, ICS)
  • © vulkane.net. All rights reserved. created by Marc Szeglat.