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Geological History of the Earth: Introduction
It is clear from the study of meteorites and samples of moon rocks that the age of our earth is 4.6 billion years. Pre-testing of the oldest rock samples on Earth for radioactive elements has shown them to be 3.9 billion years old. The most reliable explanation of the age of the earth has come from the study of radioactive materials.
Based on radioactive elements, Pierre Curie and Rutherford calculated that the earth is two to three billion years old. The French scientist Caste-de-Buffon made the first attempt to elucidate the earth’s geological history. At present, the history of the earth is divided into several Eras. These eras are again arranged sequentially into Epochs. Each epoch is again divided into periods known as Shakas (Period).
Relevant key facts related to the geological history of the Earth
Pre-Paleozoic Era
It is divided into two periods, Archean, and Pre-Cambrian.
1. Archean Period: –
There is a complete absence of fossils in the rocks of this period. Therefore, it is also called the Azoic period. Granite and gneiss predominate in these rocks, in which gold and iron are found. The Canadian and Fennoscandia Shields were formed during this period.
2. Pre-Cambrian Period: –
In this period, there was an emergence of a spineless organism (Invertebrates). During this period, invertebrates with soft skin were mainly found in the warm seas. Even though vertebrates first appeared in the oceans, the land was devoid of life. In India, the Aravalli Mountains and the Dharwad series of rocks were formed in this period.
Paleozoic Era
It is also called primary epoch. It has the following periods-
1. Cambrian Period: –
In this period, for the first time, there was an encroachment of the seas on the land areas. The oldest sedimentary rocks were formed in the Cambrian period. The Vindhyachal mountain range in India formed during this period. The shallow seas on earth kept growing and shrinking during the time. Cambrian rocks were formed in Wales of Great Britain, northwest Scotland, western England, Canada, and the United States. The first plants and animals originated in this period on earth and algae originated in the seas.
2. Ordovician Period: –
The expansion of the sea submerged half of North America, while eastern America was affected by Taconian mountain-building activities. During this period, there was an expansion of flora and sea crawlers, but the land area was still lifeless.
3. Silurian Period: –
In this period all the continents were affected by the Caledonian movement on the earth, as a result of which the mountains of Appalachian in North America, Scotland, and Scandinavia were formed. Vertebrates first appeared on the land and fishes originated in seas. That is why it is called as Age of Vertebrates. The coral organisms developed in this period. Plants originated first time on land. These plants were leafless and originated in Australia. It is also a period of extensive Caledonian mountain movements.
4. Devonian Period: –
As a result of the Caledonian movement, high mountain ranges developed on all the continents, evidence of which can be seen in Scandinavia, South-West Scotland, Northern Ireland, and East America. In ancient times, the climate of the Earth was most favorable for sea creatures, especially fish. At the same time shark fish also appeared. Hence it is known as the Fish Age. At the same time, amphibians and fern flora also originated. The height of the plants had reached up to 40 feet.
5. Carboniferous Period: –
In this period, Caledonian movements were replaced by Armenian movements, by which Britain and France were most affected. Reptiles also appeared on land. Trees up to the height of 100 feet appeared during this period. This is called the period of large trees (Glycepteris). Trees were buried in the faults that formed rocks of the Gondwana order during this period. These rocks contain coal deposits in abundance. Therefore, it is called Carboniferous Kalp or Coal Age.
6. Permian Period: –
This period saw the Variscan movement, which mainly affected Europe. The climate gradually became dry. Due to the formation of rifts as a result of the variscan movement, block mountains like the Black Forest and Vosges were formed. Mountains like Spanish Meseta, Altai, and Tianshan Appalachian were also formed in this period. During this time the development of many species of fauna and flora was seen on the land. Potash deposits were formed on the earth’s crust by the evaporation of internal lakes caused by fracturing.
Mesozoic Era
It is also called secondary epoch. It is divided into Triassic, Jurassic, and Cretaceous periods.
1. Triassic Period: –
During the period, large crawlers developed on the land. That is why it is called the Age of Reptiles. This period was the period of origin of Archaeopteris. They could walk on both land and sky. The fast-swimming lobster also emerged at this time. Mammals also began to appear. Carnivorous fish-like reptiles originated in the oceans. Frogs and tortoises originated in this period.
2. Jurassic Period: –
Creatures with crocodile-like mouths and fish-like bodies, dinosaur reptiles evolve, and lobsters continue to grow. Aquatic, terrestrial and nomadic creatures appeared. It is believed that Jura Mountain also formed during this period. Flowering plants and the first flying bird (Archeopteryx) appeared at this time. The main feature of this period was the limestone deposits, which were found mainly in France, southern Germany, and Switzerland.
3. Cretaceous Period: –
Angiosperm plants (Angiosperm) and the Rocky & Andean Mountains began to develop during the period. The appearance of large turtles was also observed in this period. Temperate deciduous forest trees such as Magnolia and Popnar have evolved. Chalky soil was deposited in northwestern Alaska, Canada, Mexico, the British Dober area, and Australia. Deccan trap and black soil were formed in India, due to fissure eruption of volcanic lava in this period.
Fig. 1.2 Geological Time Scale
Cenozoic Era
This Kalpa is also called Tertiary epoch. It is divided into Paleocene, Eocene, Oligocene, Miocene, and Pliocene periods. In different periods of this Kalpa, Alpine Mountain ranges took place and all the new folded mountains of the world such as the Alps, Himalayas, Rocky, Andes, etc. originated.
1. Paleocene Period: –
The Laramide movement during this period resulted in the formation of the Rocky Mountains in North America and mammals extended on the land. Mammals and Apes first appeared in this period.
2. Eocene Period: –
In this period, volcanoes erupted through various cracks on the surface, and crawlers on the land almost became extinct. Ancient monkeys and gibbons originated in Myanmar. Ancestors of elephants, horses, rhinoceros (rhinoceros), boars, etc. appeared on land.
3. Oligocene Period: –
The formation of Alpine Mountain began in this period. The Great Himalayas originated in the Oligocene period.
4. Miocene Period: –
Because of Alpine Mountain building activities, folds were developed all over Europe and Asia, whose direction of expansion was east west. Large size (60 feet) shark fish, procanal (tailless monkey), water birds (swan, duck) penguins, etc. originated in this period. The development of elephants also took place during this period. This is the period of origin of the middle or lesser Himalayas.
5. Pliocene Period: –
Continuous sedimentation of the seas led to the development of vast plains in Europe, Mesopotamia, northern India, Sindh, and North America. Human ancestors evolved and modern mammals appeared. Shivalik originated in this period. The deposition of sediments in the Tethys geosyncline, a water-filled basin between the Himalayan ranges and the peninsular part of India, resulted in the development of the northern plain of India.
Neozoic Era
It is also called the Quaternary epoch. Pleistocene and Holocene are its two periods-
1. Pleistocene Period: –
In this shaka or period, there was a drop in temperature due to which four ice ages were observed in Europe which are as follows – Gunz, Mindel, Riss, and Wurm. Relatively warm interglacial were observed between individual ice ages. The interglacial period between Mindel and Riss was the longest. In North America, Nebraskan, Kansas, Illinois or Iowa, and Wisconsin ice ages were observed at this time.
The interglacial period that occurred between Nebraskans and Kansan is known as Aftonian, between Kansans and Illinoian is Yarmouth, and between Illinoian and Wisconsin is Sangamon. At the end of this era, the ice sheet continued to melt, and the height of the western Scandinavian region continued to rise. Flying birds are believed to have appeared on Earth only in the Pleistocene period. Humans and other mammals evolved into what they are today.
2. Holocene or Holocene Period:
The increase in temperature resulted in the melting of the ice on the earth’s surface and the present state of the world was reached, which continues. It was at this time that sea creatures reached their present stage. The man started agriculture and animal husbandry on the land.
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