Geological History of the Earth - Geological Time Scale
INTRODUCTION
The age of our Earth, estimated at approximately 4.6 billion years, has been gleaned from the examination of meteorites and moon rock samples. Preliminary analysis of the most ancient rock samples found on Earth, focusing on radioactive elements, has revealed their age to be around 3.9 billion years.
The most dependable insights into the Earth's age have been furnished by the study of radioactive materials. Pioneers in this field, such as Pierre Curie and Rutherford, computed that the Earth's age falls within the range of two to three billion years. Additionally, the French scientist Caste-de-Buffon made one of the earliest endeavours to unravel the geological history of our planet.
In the contemporary context, Earth's history is delineated into distinct Eras, which are subsequently organised in chronological order into Epochs. Each Epoch, in turn, is subdivided into periods known as "Shakas" (Periods). This structured division aids in comprehending and tracking the Earth's geological evolution.
Geological time scale
PRE PALEOZOIC ERA
Divided into two archean and precambrian
ARCHEAN PERIOD
This period is marked by a striking absence of fossils within its rock formations, which is why it is often referred to as the Azoic period. The predominant rock types in this era are granite and gneiss, and these formations have been found to contain valuable resources such as gold and iron.
Notably, during this time, the Canadian and Fennoscandian Shields took shape. These geological features are a testament to the geological events and processes that unfolded during the Azoic period.
PRE CAMBRIAN PERIOD
During this period, a noteworthy development was the emergence of invertebrate organisms, which lack a spinal column. Invertebrates with soft, unarmored skin were predominantly present in the warm seas. Although vertebrate life initially made its debut in oceanic environments, terrestrial life was conspicuously absent.
In the Indian subcontinent, this period witnessed the formation of the Aravalli Mountains and the Dharwad series of rocks, adding to the geological history of the region.
PALEOZOIC ERA
CAMBRIAN PERIOD
During this period, a significant event occurred as the seas began to encroach upon the terrestrial land areas for the first time. The Cambrian period is notable for the formation of the Earth's oldest sedimentary rocks. In India, this era saw the creation of the Vindhyachal mountain range.
Throughout this time, shallow seas on Earth experienced cyclical expansions and contractions. Cambrian rock formations are found in various regions, including Wales in Great Britain, northwest Scotland, western England, Canada, and the United States.
This period is particularly significant because it witnessed the earliest appearance of plants and animals on Earth. In addition, algae originated in the seas during the Cambrian period, marking an essential step in the planet's biological evolution.
ORDOVICIAN PERIOD
In this period, a notable geological event occurred as the sea expanded, submerging a significant portion of North America. Meanwhile, eastern America experienced mountain-building activities associated with the Taconian orogeny. Despite these dynamic changes, the land area remained devoid of life.
During this time, there was a noteworthy expansion of plant life and sea-dwelling creatures, although the land itself remained uninhabited. These developments further shaped the Earth's evolving ecosystems.
SILURIAN PERIOD
During this period, the Earth witnessed the far-reaching effects of the Caledonian orogeny, which impacted all continents. As a result of this geological movement, the Appalachian Mountains in North America, as well as their counterparts in Scotland and Scandinavia, were formed.
The Silurian period is often referred to as the "Age of Vertebrates" because it marked the first appearance of vertebrate life on land. Additionally, significant developments occurred in the seas, with the origin of fishes. Coral organisms also underwent noteworthy evolution during this time.
Crucially, this period saw the emergence of plants on land for the first time. These early land plants were devoid of leaves and had their origins in Australia. The Silurian era was characterized by extensive Caledonian mountain-building movements, which played a pivotal role in shaping the Earth's geological and biological landscape.
DEVONIAN PERIOD
The Caledonian movement left a lasting mark on the Earth, giving rise to towering mountain ranges on every continent. Remnants of this movement are visible in regions such as Scandinavia, South-West Scotland, Northern Ireland, and Eastern America.
In antiquity, the Earth's climate was highly conducive to marine life, particularly fish. It was during this period that shark fish made their debut, earning this era the moniker "Fish Age." Concurrently, amphibians and ferns also had their origins. Some of these ancient ferns grew to impressive heights, reaching up to 40 feet, marking a remarkable chapter in the evolution of plant life.
CARBONIFEROUS PERIOD
During this period, the Caledonian movements gave way to the Armenian movements, which had a significant impact on Britain and France. Notably, reptiles made their appearance on land during this time, marking a crucial milestone in the evolution of terrestrial life.
Another remarkable development in this era was the emergence of trees, some of which reached towering heights of up to 100 feet. This period is often referred to as the "Age of Large Trees" or the "Glyptceris period."
It was also during this time that trees were buried in the geological faults that ultimately formed rocks of the Gondwana sequence. These rocks contain abundant coal deposits, leading to the era being commonly known as the "Carboniferous Kalp" or the "Coal Age." The significant coal reserves found in these rocks have had a profound impact on Earth's industrial history.
PERMIAN PERIOD
In this period, the Earth experienced the Variscan orogeny, primarily affecting the continent of Europe. Over time, the climate gradually transitioned to a drier state. The Variscan movement resulted in the creation of rifts, leading to the formation of block mountains, including notable features such as the Black Forest and Vosges.
Additionally, this period witnessed the formation of several other mountain ranges, such as the Spanish Meseta, Altai, Tianshan, and the Appalachian Mountains. These geological developments significantly altered the landscape of the Earth.
During this time, there was a proliferation of diverse species of fauna and flora on the land, contributing to the planet's evolving ecosystems. Moreover, potash deposits were formed in the Earth's crust through the evaporation of internal lakes resulting from the fracturing of the Earth's surface.
MESOZOIC ERA
TRIASSIC PERIOD
This period is often referred to as the "Age of Reptiles" because it marked a significant development with the emergence of large land-dwelling reptiles.
During this era, a noteworthy species called Archaeopteris came into existence. What made Archaeopteris particularly remarkable was its ability to navigate both land and sky, setting it apart as an early example of a creature with dual adaptability.
Furthermore, this period saw the rapid emergence of various life forms. Fast-swimming lobsters made their appearance in the oceans, and mammals began to appear on land. In the aquatic realm, carnivorous fish-like reptiles originated.
On the terrestrial front, this era witnessed the origin of frogs and tortoises, contributing to the diversification of life on Earth.
JURASSIC PERIOD
This period is often referred to as the "Age of Reptiles" because it marked a significant development with the emergence of large land-dwelling reptiles.
During this era, a noteworthy species called Archaeopteris came into existence. What made Archaeopteris particularly remarkable was its ability to navigate both land and sky, setting it apart as an early example of a creature with dual adaptability.
Furthermore, this period saw the rapid emergence of various life forms. Fast-swimming lobsters made their appearance in the oceans, and mammals began to appear on land. In the aquatic realm, carnivorous fish-like reptiles originated.
On the terrestrial front, this era witnessed the origin of frogs and tortoises, contributing to the diversification of life on Earth.
CRETACEOUS PERIOD
During this period, Earth saw some significant changes. Angiosperm plants, which produce flowers and fruits, started to develop. The Rocky and Andean Mountains began to take shape, shaping the landscape.
Large turtles made their appearance during this time, adding to the diversity of life on Earth. We also witnessed the evolution of temperate deciduous forest trees like Magnolia and Poplar.
Geologically, chalky soil was deposited in various regions including northwestern Alaska, Canada, Mexico, the British Dover area, and Australia. In India, the Deccan Traps and black soil were formed due to volcanic eruptions that released lava through fissures in the Earth's crust. These geological events left a lasting impact on India's landscape.
CENOZOIC ERA
PALEOCENE PERIOD
The Laramide movement in this period played a crucial role in shaping the Rocky Mountains in North America. It was also a time when mammals started to expand their presence on land. Additionally, this period witnessed the first appearance of both mammals and apes, marking significant milestones in the evolution of life on Earth.
EOCENE PERIOD
During this period, volcanoes erupted through cracks on the Earth's surface, and land-dwelling creatures, especially crawlers, were at risk of extinction. In Myanmar, ancient monkeys and gibbons made their debut. On the land, the ancestors of elephants, horses, rhinoceroses, and boars began to appear, contributing to the diversity of life on Earth.
OLIGOCENE PERIOD
During this period, the formation of the Alpine Mountains commenced. The Great Himalayan mountain range, which is one of the world's most prominent features, had its origins in the Oligocene period.
MIOCENE PERIOD
The Alpine Mountain-building activities during this period led to the development of folds across Europe and Asia, primarily expanding in an east-west direction. It was also a time when various significant species came into existence, such as large-sized shark fish measuring up to 60 feet, tailless monkeys known as proconsul, water birds like swans and ducks, and even penguins.
The evolution of elephants also marked a key development during this period. Importantly, it's the era when the middle or lesser Himalayan mountain range began to take shape, further shaping the Earth's landscape.
PLIOCENE PERIOD
Continuous sedimentation in the seas during this period gave rise to the formation of extensive plains in regions such as Europe, Mesopotamia, northern India, Sindh, and North America. This sedimentation process significantly shaped the geography of these areas.
It was also a time when human ancestors continued to evolve, and modern mammals emerged, contributing to the diversity of life on Earth. The Shivalik mountain range originated during this period, adding to the Earth's geological features.
The deposition of sediments in the Tethys geosyncline, a water-filled basin situated between the Himalayan ranges and the peninsular part of India, played a pivotal role in the formation of the northern plains of India, further influencing the topography of the subcontinent.
NEOZOIC ERA
PLEISTOCENE PERIOD
During this time period, there was a notable drop in temperatures, leading to the occurrence of four ice ages in Europe: Gunz, Mindel, Riss, and Wurm. These ice ages were separated by relatively warmer interglacial periods. The interglacial period between Mindel and Riss was the longest.
In North America, several ice ages were observed, including the Nebraskan, Kansas, Illinois, Iowa, and Wisconsin ice ages. These ice ages were punctuated by interglacial periods, with the Aftonian between Nebraskan and Kansan, Yarmouth between Kansan and Illinoian, and Sangamon between Illinoian and Wisconsin.
Towards the end of this era, the ice sheets continued to melt, and the western Scandinavian region's elevation increased. It's believed that flying birds made their appearance on Earth during the Pleistocene period. Notably, this period witnessed the evolution of humans and other mammals into the forms we recognize today.
HOLOCENE PERIOD
The rise in temperature led to the melting of the Earth's surface ice, which brought us to the present state of the world, a condition that persists today. It was during this period that sea creatures evolved to their current forms. Additionally, humans began practicing agriculture and animal husbandry on land, marking the beginnings of these crucial aspects of human civilization.
