GEOLOGICAL AGE OF ROCKS AND LAYERS
In the descriptions of rocks and deposits, it is important to define their geological age. This is because it makes it easier to find similar deposits in other areas, especially the neighboring ones. This also applies to deposits of precious stones.
|Division of the history of the Earth|
Presence of fossils in rocks, that is, the fossilized remains of organisms, is of great importance for comparing the age of rocks. Especially these species of animals and plants, who lived shortly, but in large areas they are of great value to a geologist. Based on fossils found only in a given period (index fossils) rocks, they contain can be easily identified as being of equal age even then, when they occur in distant areas. Fossils are used to determine the relative age of rocks, which is the basis for the division of the history of the Earth into eras, geological periods and epochs. Physico-chemical methods, involving the study of radioactive isotopes present in rocks, the absolute age of minerals and rocks is determined. This research shows, that the duration of geological eras was very different. The Cenozoic era lasted over 60 min years, Mesozoic - approx 170 million years, paleozoicza — 340 min years. The oldest eras - Proterozoic and Archaic - lasted much longer, because approx 5000 min years.