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Geological time

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already many years geologists, leaning against the data of researches of rocks, try to establish age of the Earth, but still rather recently they were rather far from success.

The majority of geologists considers as the Father of modern geology James Gettona (1726-97), the Scottish doctor and the scientist who has created in 1785 on the basis of researches and supervision of natural processes work "КхюЁш  Гхьыш". He one of the first has understood that the surface of the Earth all time changes. Under the influence of the weather phenomena - for example, a frost - rock gradually collapses, and the rivers bear its fragments in lakes and the seas, where from such adjournment collecting by layers as sand and silt, are formed new breeds - sedimentary.

Warmly and pressure

Warmly and pressure He asserted that the heat and pressure transform layers of sedimentary breeds being deeply, changing their nature and transforming in metamorficheskie. He also has characterised the third type of rocks (magmatic), including basalt and the granite generated from the fused material - for example, lavas.

Getton has become interested in relative age of rocks. Having investigated some breeds in Scotland, he has found out that the top layer of one rock from the bottom layer another sometimes separates a huge time interval. This border has been named by a disagreement surface. Not consent naplastovanija the exposure and erosion of already formed rock grow out. Much later, when such breeds once again will disappear under a sea smooth surface, over them much younger layers start to be formed.

Getton understood that processes investigated by it occur slowly, and therefore the history of the Earth should be extremely long. And though estimate its age it could not, Getton has concluded that "эшъръш§ instructions neither on the beginning of the Earth, nor on its end at us not шьхх=ё ".


Geological mapping

Geological mapping the Important contribution to understanding of geological time was brought by one more British - engineer William Smith (1769-1839). Smith worked on building of channels. While workers dug trenches, Smith collected the fossils which were coming across in underground layers. He has noticed that many fossils meet in strictly certain layers of rock, and layers always go in the same order and contain the same sequence of fossil remains.

Smith has come to a conclusion that breeds meeting in different places which contain the same fossils, have identical age. And still he has decided that breeds it is possible to arrange in relative time sequence, that is to assert that this or that layer earlier or later though to tell, how much, it is impossible. Having collected this information, breeds it is necessary to approach very circumspectly. For example, in folded breeds one layers lie naklonno, here and there almost vertically. Others are thrown back, and more ancient layers appear above later.

Geologists, however, have learnt to define, how folded breeds are formed. On a surface of some layers of rock it is possible to notice, for example, the traces of ripples left a current, waves or winds. There are also other characteristic signs distinguishing a surface of a layer of firm breed - the apertures dug by hearts and other animals in those days when it still was soil.


the Geological column

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Applying such methods, geologists have understood sequence in which there was a formation of layered breeds on a planet. It has allowed to construct a scale of history of the Earth (a geological column). In breeds age more than 590 million years of fossils are a little. Until recently these most ancient breeds could be divided on two basic groups. The oldest, not containing any fossils, named arheozojskimi, later in which fossils though came across, but is extremely rare - proterozojskimi. The breeds generated in last of 590 million of years where fossils meet everywhere, were called fanerozojskimi.


Three long era

Because of abundance of various fossils in fanerozojskih breeds time of their occurrence subdivide for three era - paleozoj (letters, "фЁхтэ   цшчэі"), mezozoj ("ёЁхфэ   цшчэі") and kajnozoj ("эютр  цшчэі"). Each era shares for the periods. The first period of a Paleozoic era - cambrian. Modern geologists, as a rule, carry now all breeds formed before the cambrian period (proterozojskie and arheozojskie), to dokembrijskim.

Names of some periods reflect names of districts in which breeds of corresponding system for the first time have been studied. For example, kembry has been named in honour of Cambria (the Latin name of the Wales), and Perm - the Russian Perm. The Ordoviksky and Silurian periods are obliged by the names to the ancient tribes occupying Britain.

The Coal and cretaceous periods are named by name the breeds connected with them. Besides, the American geologists split up the coal period for two: missisipsky (bottom coal) and pensilvansky (top coal) the periods.


Systems

The Kajnozojsky era shares for two periods: tertiary and chetverichnyj. These names - a vestige of old classification in which all adjournment have been carried to four basic categories: primary, secondary, tertiary and chetverichnym. Terms "яхЁтшёэ№щ" and "т=юЁшёэ№щ" have gone out of use, but two another has carried more.

The Breeds formed in tertiary and chetverichnom the periods, contain so many organic remains that these pieces were divided also on more fractional, named epoch, and by those in turn on about some centuries: so, geologists write about lednikove (English Ice Age - "ыхфэшъют№щ тхъ"), come at the time of plejstotsena - the first epoch chetverichnogo the period. The Stratigrafichesky scale has given representation about relative age of rocks and has established names er, the periods and epoch which could be applied all over the world, but each of these pieces how many lasted, geologists did not know.


And how old is she?

Scientific attempts to define age of breeds began to be undertaken in the end of XIX century. Charlz Lajel (1797-1875), the outstanding geologist and friend Charlza of Darwin, started with at what stage of evolution there were fossil organisms. So, by its estimations, the piece between the beginning of the cambrian period when they began to appear for the first time much, and our time was equal approximately to 240 million years. But its calculations were inexact also values had no.

Known British physicist Calvin (1824-1907) tried to define age of the Earth several methods. One of them leant against speed of rotation of the Earth and quantity of heat radiated by the Sun. The hypothesis has been put in the basis of another that first the Earth represented the fused sphere so then it was necessary to count up as long it needed to be cooled to present temperature. By calculations left that to the Earth no more than 100 million years. But also they were far from true.


Absolute age

It was possible to prove the Inaccuracy of calculations of Calvin after opening in 1896 of the phenomenon of a radio-activity. The radioactive substances which are found out in some breeds, let out particles of high energy and thereof break up with constant speed. For example, an end-product of disintegration of a radioactive element of uranium is lead, therefore age of the sample of uranium it is possible to establish, having measured quantity of lead containing in it.

Radio isotope dating has allowed geologists to establish absolute age of rocks, the beginning and duration er, the periods and epoch. However, from time to time, when find and new samples of the radioactive breed date, habitual figures should be reconsidered. Radiometric methods have shown also that the age of a planet the Earth is measured at all by millions, and billions years.