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Geological History of Earth Origin | Article 7

The geological history of the earth or the geological clock refers to the reconstruction of evolutionary sequence of the geological events involving the information of various zones (crust, mental and core) of the Earth, formation and evolution of geomaterials, formation and development of mountains and faults, evolution of different lives etc.the whole geological history right from the origin of the earth to its present from has been divided into major and minor periods on the basis of forms of life, characteristics of deposits, places of Rock formation, major tectonic events etc.the whole geological history of the earth has been divided into five eras based on five major groups of deposit as follows:-

Major Groups of Deposits (form youngest to oldest)
Cenozoic group
Cenozoic group (era of recent life)
Mesozoic group
Mesozoic group (era of medieval life)
Proterozoic (era of earlier life)
Archeozoic (era of primeval life)

Each era is numbered in sequence as first (primary), second (secondary), third (tertiary), fourth (quaternary) and is named period. Further, each period is divided into several apochs.The names of apochs have been assigned on various grounds e.g.names of the places of characteristics system of deposits, the names of tribes, the characteristics of deposits, dominance of certain elements and minerals etc as follows-

Palaeo (ancient), zoe (German) - life
Mesos (German) means middle
Kainos (German) means new
Cambrian or Wales (place) in U.K.
Ordovician (a British tribe in N.Wales)
Silurs (a British tribe in S.Wales)
Devonshire (place and region in U.K)
Dominance of carbon (coal)
Perm (a province in earth while USSR)
Three-fold division of deposits in Germany, ‘trias’ means triple
After jura mountains in Switzer - land
Creta (Latin) means chalk, domi-nance of abundant deposits of white writing chalk
Eos means day break
Oligos (German) means little
Meion (German) means smaller
Pleion (German) means greater
Holo means complete
Pleistos  means most

Precambrian period

The precambrian period started 700 million year B.P.the earth changed from gaseous state to liquid state. The solid outer crust was formed due to cooling and solidification of liquid materials.this phase was followed by the formation of dense atmosphere surrounding the earth.due to gradual but continued cooling and contraction of the earth and resultant condensation of water vapout began the precipitation process which ultimately resulted into the formation of river and seas. The sequence of warm climate was broken by many glacial periods. The rocks were subjected to maximum metamorphism due to heat and pressure. Among the plant kingdom only Marine grasses were evolved, soft bodied invertebrate animals were involved in warm seas but the land areas were devoid of animals.

Cambrian period
Cambrian period

Cambrian Period

The Cambrian period lasted from 600 million years B.P. the Earth surface was characterized by shallow seas and the land areas were frequented by transgressions and regression of seas. Cambrian Rock of Wales, north west Scotland, Western England, Canada and USA were formed during this period. Europe was characterized by volcanicity but no trace of any mountain building could be found. The earth's surface was characterized by warm and uniform climate. Evolution of plants was still confined to the seas only. most of the vertebrate animals including thousand species were evolved in the seas but they are not found at the present time. These animals depended on Marine grasses for their food. No land animals could evolve during this period.

Ordovician period

Ordovician period

Ordovician Period

The ordovician period continued from 500 million years to 440 million years B.P. The transgressional and regressional faces of seas continued. Many shallow seas became dry because of depression of sand and mud. Ordovician rocks were formed in north west Europe and North America. This period was characterized by the initiation of mountain building. Marine areas were affected by active vulcanicity. The climate on the entire Earth's surface was warm and has no zonal pattern of climate was evolved. Vegetation and animal were still confined to the seas only. Animal species included only vertebrates.

Silurian period

Silurian period

Silurian period

The silurian period spread from 440 million to 400 million years B.P. sea level was characterized by the periodic rise and fall which introduced changes on Earth's crust. The mountain building continued but the volcanicity was less active than during ordovician period. On an average the climate was warm but some areas were also characterized by relatively in dry climate. Leafless plant were evolved on the land areas. The remains of such vegetation have been found in Australia.there was increase in the species of vertebrate animals of marine environment. The plant community was diversified because of evolution of new species. Corals were evolved at large scale. Plants evolved for the first time on land areas.

Devonian period

Devonian period

Devonian period

The devonian period continued from 400 to 350 million years B.P. and experienced increase in Land and decrease in Marine areas. Mountain building and vulcanicity were more active. The newly formed mountain was subjected to denudational and eroded material word deposit as pebbles, sands and red sandstones.most of the areas of north west Europe and North America were characterized by worm and semi-arid climate. The remaining areas were dominated by uniform climate. the Earth surface was covered with a green vegetation as the plants develop their leaves, branches, stems and roots. the vegetation comprised of small shurbs to tall trees measuring 14-15 metre in height. Fern vegetation was evolved by the end of this period. Marine vertebrate animals were again evolved.this period was characterized by the evolution of large number of species of fish. Amphibians were evolved towards the end of this period. There were dispersal of vertebrate animals from sea to the land areas due to evolution of such Flora on land areas which could provide them food.

Carboniferous period
Carboniferous period

Carboniferous Period

the carboniferous period spread from 350 million to 270 million years B.P. and was characterized by numerous small and shallow sea on the Earth's surface. most of the areas of Europe including Russia was submerged under water. some land areas in North America and Europe were depressed and thus were covered with water giving birth to swamps. The coal formation of northern hemisphere was accomplished during this period. dry climate continued for most period but some areas were characterized.

The geological time scale
The geological time scale

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