Geological History of the Earth

Hello friends,

    Today, we will discuss the geological history of the Earth, as it is well known that the planet did not always possess its current form; nor can it be said with certainty that this form will persist into the future. Our Earth holds countless records that reveal the conditions of the ancient past, with fossils being the most significant among them. Scientists worldwide are able to determine the age of these fossils through various research methods. While many of us are familiar with the Carbon-14 (C-14) dating method, there are still many who are unaware of it; this technique is used to ascertain the age of fossils and rock formations. Furthermore, there are many people who still explain the origin and evolution of the Earth based on stories from religious texts, presenting them as the absolute truth—accounts that lack even the slightest trace of logic, research, or scientific validity.

    Let me first mention that the study of Earth's oldest rocks reveals that life on the Earth's crust originated between 1 and 1.5 billion years ago. However, fossils discovered either on the surface or within the Earth's interior are no older than 500 million years. The history of the Earth was first divided into seven epochs by the French scholar Buffon. Since the Earth's inception, the processes of change on the crust, the evolution of landforms and topography, and the development of flora and fauna have proceeded and will continue to proceed in a specific sequence across various time intervals and eras. Currently, Earth's history is understood in terms of five eras and seventeen periods.

No.	Mahakalpa (Great Eon)	Kalp (Eon)	Start Time (Earlier)
1.	Eozoic Era	1. Archaean	--
		2. Pre-Cambrian Algonican	Approximately 2.5 Billion Years
2.	Palaeozoic Era	1. Cambrian	600 Million Years
		2. Ordovician	500 Million Years
		3. Silurian	440 Million Years
		4. Devonian	400 Million Years
		5. Carboniferous	350 Million Years
		6. Permian	270 Million Years
3.	Mesozoic Era	1. Triassic	220 Million Years
		2. Jurassic	180 Million Years
		3. Cretaceous	135 Million Years
4.	Kainozoic or Tertiary Era	1. Eocene	70 Million Years
		2. Oligocene	40 Million Years
		3. Miocene	20 Million Years
		4. Pliocene	11 Million Years
5.	Neozoic or Quaternary Era	1. Pleistocene	1.0 Million Years
		2. Holocene	10.0 Thousand Years

1. The Oldest or Archean Eon:

    The various rocks forming Earth's outer layer (crust) originated during this eon. It was the longest-lasting eon. Early in this eon, heavy rainfall cooled the Earth's surface; consequently, plant and animal life was virtually non-existent. Ocean waters were not saline.

    During this eon, folding occurred in accumulated sediments due to various geological movements. Lava erupted through fissures in certain areas, initiating the process of mountain formation. Mountain-building events occurred five times during this eon. It concluded with the final 'Charnian' crustal disturbance. The mountains formed at that time are no longer visible today due to erosion. Based on the analysis of radioactive elements, these mountains are estimated to be approximately 1 billion years old.

    During this eon, the supercontinent Pangea broke apart into the Laurentia Shield, Baltic Shield, Angaraland, and Gondwanaland. In India, the Dharwar, Cuddapah, and Vindhyan rock systems were formed.

2. Paleozoic Era:

    This era is highly significant because it marked the first appearance of invertebrate organisms and grass-like vegetation on Earth. Additionally, this era witnessed the encroachment of seas onto the continents. This era is divided into the following six periods -

(A) Cambrian Period: The solid Earth's crust was formed during this period. The formation of seas also dates back to this time. The first fossils are found in the limestone and sandstone rocks formed during this period.

(B) Ordovician Period: This period is known for volcanic eruptions, the large-scale expansion of seas over continents, and the emergence of the first grass-like vegetation in the oceans. Distinctive organisms known as Trilobites and Graptolites evolved during this time.

(C) Silurian Period: This period saw the evolution of fish in the oceans and diverse vegetation on land. Invertebrate organisms emerged during this era. Extensive mountain ranges were formed through Caledonian earth movements.

(D) Devonian Period: Due to the proliferation of fish in marine environments, this period is known as the 'Age of Fish.' It also witnessed the rise in the height of Caledonian mountains and the formation of red sandstone and limestone rocks.

(E) Carboniferous Period: This period is known as the 'Coal Age.' A hot and humid climate led to heavy rainfall, resulting in the growth of dense forests. These forests were submerged due to the subsidence of continents, and sediments were deposited over them. Coal was formed due to forests remaining buried under rock strata for extended periods. During this time, mountain ranges were created through the 'Armorican' earth movements, and shallow seas developed as a result of increased sediment deposition. There was a proliferation of both terrestrial and aquatic life forms.

(F) Permian Period: Fold mountains were formed during this period as a result of 'Hercynian' earth movements. These movements occurred 130 million years after the 'Caledonian' earth movements. Aridity increased during this period due to a rise in temperature.

3. Mesozoic Era:

    This era marks the period when gigantic animals, birds, and flowering trees emerged. Evidence indicates that the climate of the Antarctic continent remained warm during this time. There is evidence of Gondwanaland existing to the south of the Tethys Sea. This era is divided into the following three periods -

(A) Triassic Period: Small mammals evolved during this period. The South Pole was glaciated, while the North Pole was arid (desert-like). Gondwana existed as a single, unified landmass. Evidence of glacial flow is found in southern India.

(B) Jurassic Period: Widespread warm and dry climatic conditions on land led to the emergence of diverse life forms animals and birds across land, water, and air. Some animals were gigantic and formidable, resembling elephants and rhinoceroses. Dinosaurs originated during this period. Tectonic movements known as the Nevadan and Laramide orogenies also occurred during this time. In India, the Rajmahal and Sylhet hills were formed during the Jurassic Period.

(C) Cretaceous Period: Evidence of lava flows is found from this period. In India, there is evidence of lava flows covering an area of ​​ 500,000 square kilometers on the Deccan Plateau. Additionally, trees such as oak, walnut, willow, and coconut emerged during this period. Subsidence of land occurred in the Northern Hemisphere.

4. Cenozoic Era:

    This era began approximately 40 million years ago. The first early humans appeared during this period. By this time, the Earth had cooled significantly. Due to the cold and glacial conditions, there was a drastic decline in the population of reptiles. Meanwhile, Alpine tectonic movements led to the formation of fold mountains stretching from Gibraltar to the Himalayas across Eurasia, as well as the creation of Northern Europe and the Indus-Ganga plains. The shifting of the Gondwana landmass resulted in the separation of regions such as Africa and the Deccan Plateau. Evidence of volcanic eruptions is also found in certain areas. This era is divided into the following four periods -

(A) Eocene Period: The formation of the Himalayas began during this period. Subsidence of the European continent led to the expansion of seas; specifically, the Atlantic and Indian Oceans expanded. Tropical climate conditions facilitated the growth of palm trees in regions extending from England to Greenland. Giant reptiles went extinct, though sea cows and whales persisted. Numerous mammalian species emerged on land; animals such as elephants, horses, rhinoceroses, pigs, crocodiles, and turtles developed. Early apes and gibbons also appeared.

(B) Oligocene Period: Apes, the ancestors of humans, evolved during this period. The retreat of seas led to an expansion of land areas. The Alps in Europe were formed. A shift to a cooler climate caused the destruction of forests in some regions. Aquatic life forms like crabs and snails flourished, while diverse mammals evolved on land; species such as cats, dogs, bears, and the ancestors of modern elephants developed. 

(C) Miocene Period: During the Miocene Period, due to active volcanism, powerful tectonic movements, and significant climatic variations, the seas contracted, fold mountains expanded, and diverse flora spread; additionally, giant sharks, penguins, aquatic birds, and ducks evolved.

(D) Pliocene Period: During this period, the Shivalik range was formed as a result of the final uplift of the Himalayas. The present-day configuration of seas and oceans was established. On land, large mammals declined while hominids (Ape-Like Ancestors) evolved. Marine flora and fauna developed into their present-day forms.

5. The Cenozoic Era or the Quaternary Era:

    This is the most recent era in the history of life on Earth. It was during this era that modern humans and flora emerged. The development of human intelligence and the evolution of birds are also products of this era. This era is divided into the following two parts -

(A) Pleistocene Period: Approximately one million years ago, during this period, the Earth's surface was covered by an extensive ice sheet. This glaciation was far more widespread and extensive than that of the Carboniferous period (350 million years ago); consequently, this period is known as 'The Great Ice Age.' This ice sheet receded only 10,000 years ago.

    

In North America, four glacial advances (ice ages) occurred: the Nebraskan, Kansan, Illinoian, and Wisconsin. Interglacial periods characterized by rising temperatures occurred between these ice ages and are known as the Aftonian, Yarmouth, and Sangamon, respectively. Penck and Brückner identified four ice ages in Europe: the Günz, Mindel, Riss, and Würm.

    

According to Thornbury, glaciation during the Pleistocene period led to the formation of numerous distinctive landforms. The Great Lakes in North America, various lakes in Europe, and swamps in Siberia were formed during this time. The recession of the ice sheet led to the development of the fjord coasts of Norway. Glacial moraines are found in many locations. Glaciation caused the destruction of coral organisms in the oceans, which subsequently re-emerged as the ice melted. The ice destroyed Europe's delicate vegetation, leaving only hardy flora to survive. Human species evolved, and climate change triggered the migration of animal life.

 

(B) Holocene Period: Modern humans emerged during this era. Approximately 10,000 years ago, forests developed in the European region as ice sheets retreated and the climate warmed. Vast deserts formed in North Africa and Central Asia, and landforms took on their present-day shapes.

    The above description makes it clear that the evolution of the Earth and its biological wealth has occurred through a gradual process rather than through any divine power. Scientists continue to work in this field today, conducting ongoing research to address future complexities. Scientists estimate that the Earth's surface temperature will rise by 1.5°C to 4.5°C by 2050, as authenticated studies spanning the last 120 years confirm a progressive warming of the Earth's surface. If this occurs, glaciers will melt, and sea levels will rise.