Earth as a planet probably is about 5-6 billion years old. The absolute age of the earth's crust is estimated at 4.5 billion years . In the oldest rocks on the Earth, zirconia was found to reach the age of 4.3 billion years, which had to be formed in older rocks.
In addition to the absolute age of rocks, the relative age is defined as the order in which they are formed.
In the reconstruction of earth's crust history, the principle of updating , which assumes that the same processes as in the past and follows the same principles - "the same causes, under the same conditions, have the same effect."
The absolute age of rocks is determined by means of radioactive elements, exploring in the rock the content of the radioactive element and the content of its decay products. Numerous radioactive elements are used to date, from which the names of isotopic dating methods are derived:
Uranium-lead - uranium 238, disintegrating in a total of 4.47 billion years lead 206 - the method used to date the oldest rocks;
- rubidium-strontium - the rubidium isotope 87 is converted into strontium 87 isotope over 49 billion years - a method useful for dating granites counting more than 100 million years;
Potassium-argon -radioactive potassium 40 is converted into argon 40 over 1.3 million years - a method used for dating rocks several million years old (especially basalt);
- Radioactive carbon (14C) - is used to determine the age of organic debris. The half-life of the coal is 5370 years, so the method is only used for young sediments, ranging from a few hundred to 50,000. years.
The absolute age of rocks is also determined by the use of earth magnetism. Magmatic rocks and some sediments at the time of formation achieve permanent magnetization consistent with the magnetic field. By studying the magnetism of rocks dated to radiometric methods, their absolute age can be confirmed on the basis of cyclic magnetic poles.
In the study of relative age rock use the following methods:
stratigraphic - determining the order of rock layers - in the rocks lying horizontally the oldest lie deepest, in rocks folded or fractured, all rocks are older than the deformation itself;
Petrographic - taking into account the conditions of the formation of individual rocks, eg basalt testifies to volcanism, limestone of the sea;
tectonic - determining events based on inconsistencies in the arrangement of rock layers;
geomorphological - determination of events based on the study of surface forms of the Earth;
paleontological - determining the age and conditions of formation of rocks on the basis of traces of plant and animal remains, or fossils . Particularly important are the fossils of fossils , ie the remains of these organisms, which, in comparison to the Earth's age, lived in a short period of time but were present in large areas. The paleontological method allowed for dividing the history of the Earth in