Brief History of the Earth


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This universe is constantly expanding. There are more than a billion undiscovered galaxies in this universe that originated out of a big bang. One such, fortunately, the discovered galaxy is of ours, the Milky Way galaxy. In chronological order, this galaxy contains thousands of solar systems and we are only aware of one or two including the one in which we reside.

Our solar system, as we all know, consists of eight planets, sun, and stars. The beautiful earth which we share with other species had to undergo a long journey of revolution which began approximately 4.6 billion years ago.

The journey started with nebula, which was a cluster of gases spinning around and collapsed into itself due to the mass and crushed all the materials into a disc. This disc was called the protoplanetary disc. Due to the pressure and constant revolving of gases, a body of heavy mass was formed in the centre of this storm.

It was called the sun, which was made up of nearly 98% of Helium and Hydrogen, and the rest of the mass, mainly rocks and gases started clumping together in various spots called planetesimals. Slowly and gradually these little clumps started withdrawing more mass from the cloud due to gravitational forces and emerged out like planets.

These planets were formed after 100,000 years of the formation of the sun. However, Jupiter and Saturn were formed first, the gas giants followed by Uranus and Neptune, the ice giants, and then four terrestrial planets Mercury, Venus, Earth, and Mars were formed.

When the Earth was newly formed, around 4.56 billion years ago, a mars-sized body thumped into the surface ejecting a large mass of our planet into space which formed a ring around the earth for a couple of periods before merging into the moon. 

At the same time, the gases which were still swirling around the Sun created gravitational forces which started pulling Jupiter towards itself, but thanks to the formation of Saturn that it pulled the gigantic Jupiter to its current position. This movement of Jupiter created havoc in the system as it bombarded its supporters, called Trojan asteroids into other planets.

This period where all the planets were going through this bantering of asteroids were called the Late phase of Bombardment. In this period only, the solar wind swept away the remaining cloud of gases and dust.

Earth was still cooling down from the collision of asteroids and other bodies and was very active volcanically at that time. Some meteorites or asteroids which were formed of water, ice brought water to the earth in the form of vapours and when the earth cooled, these vapours condensed and poured down as rain, creating oceans and rivers.

The lava was still flowing on the surface beneath the newly created oceans and continued for around 700 million years. This early period of earth formation was known to be Precambrian aeon. 

The studies of the rock revealed all the transformation that earth had gone through and hence, the periods were divided into aeons which are further divided into era followed by periods.

After 100 million years of the formation of Earth, the temperature drops down to the degree where the formation of crust started. But the atmosphere was still very toxic containing carbon dioxide, nitrogen, and sulfur majorly. Fast forward to half millions later, small patches of landmass started appearing.

There was no ozone layer at that time to protect our atmosphere from UV radiation due to the absence of Oxygen. Hence, the atmosphere was protected by its magnetic field from the solar wind; otherwise, it would’ve stripped off.

But lack of oxygen didn’t stop the formation of life which started around 4.1 billion years ago in water. The organisms who have flagged the bearer of life were zircons, prokaryotic organisms that thrived on reducing the nature of the earth.

Around 3.5 billion years ago, two supercontinents, which were about the size of India called Vaalbara and Ur, were formed. They were the first landmass to be seen, hence, carried the name of supercontinents, albeit they are mass.

Hydrothermal vents which are very few today were created during this period when lightning hit some small ponds or deep surface of the earth. This created a form of energy for primitive organisms to use and sustain themselves. They started absorbing UV light instead of visible and started emitting oxygen.

Unicellular organisms evolved with time and their cells become much more sophisticated with organelles and eukaryotes came into the picture who could prepare their food with the help of mitochondria. 

Hence, around 2 billion years ago the earth finally started breathing with oxygen due to the flourishment of cyanobacteria. This marked the beginning of the biological era.

Meanwhile, Vaalbara split into two parts which are today known as Australia and Africa. A new landmass called Kenorland appeared which floated around the equator for many years before splitting up. This rise in oxygen was called the great oxygenation event which led to the two greatest events in history, the first extinction event and the first ice age.

The major extinction event which has happened in history took place due to sudden change in the global climate and there have been 24 extinctions in the Earth’s history before the humans came around 200,000 years ago. The biggest 5 extinctions were known as big five which have proofs in the history with proper documentation.

Hence, due to an increase in pure oxygen in the atmosphere, many species were not able to tolerate increased levels of oxygen. Many species that were taking birth at this time were also dying simultaneously. Hence, the great oxygenation event turned out to be the first known extinction event.

The other major event which happened because of the excess of the oxygen was the formation of polar caps and glaciers because oxygen removed the greenhouse gases, resulting in temperature drop less than 5 degree Celsius than normal temperature.

This resulted in longer periods of very cold temperature which resonates with the warm temperature called the inter-glaciations period. The Great Oxygenation marked the beginning of the first ice-age amongst the five ice-ages’ earth has seen. 

We are in the middle of the fifth ice-ages inter-glaciations period.

Written by - Chavi Goel
Edited by - Ivanova



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