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How was the Earth Formed?

Bidisha Mukherjee
The Earth is the third planet in the solar system. It has undergone several geological changes before it evolved into its present form. To know more, read on...
Earth formed approximately 4.5 billion years ago. Initially, it lacked an atmosphere and surface water bodies, vastly different from its present state.

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Research scientists widely accept that the sun, planets, and their satellites in our solar system formed from a solar nebula—a vast spiral cloud comprising dust particles and various hot gases.
Solar nebula contracted about 4.6 billion years ago, possibly due to a nearby stellar explosion, leading to decreased temperature and increased rotation.
As a result of cooling, shrinking and faster rotation, the outer part of the cloud got detached from the main body. The solar system was formed out of one of these detached rings of the gas cloud.
The sun formed at the center of the shrinking disk, while outer parts condensed to form protoplanets. Earth emerged from one such cluster, cooling until gases turned to liquid or lava.
As the temperature decreased, lava solidified, forming Earth's crust. Dense metals like iron sank to the center, creating the core. The remaining lava became the mantle beneath the crust.
As Earth cooled, steam escaped from its crust. Volcanic eruptions released steam and gases. Geologists suggest collisions with ice-containing comets brought water to Earth.
When Earth was hot, water vapor surrounded it. As Earth cooled, vapor condensed into clouds. Rainwater collected in craters from comet impacts, forming oceans.
In its early stage, Earth's atmosphere was hydrogen and helium. Weak gravity caused loss of these gases into space.
Comet collisions enriched Earth with water and essential gases like carbon dioxide, methane, nitrogen, and ammonia. Volcanic eruptions also contributed to forming Earth's new atmosphere.
In the new atmosphere, free oxygen wasn't available as it was bound by hydrogen or other elements. The absence of an ozone layer exposed Earth's surface to ultraviolet radiation.
Significant amount of free oxygen was found in the atmosphere only after life forms came to the Earth when the photosynthesis process supplied oxygen to the atmosphere.
The current continents formed from a single landmass fragmentation. Earth's crust consists of large plates on a liquid mantle, moving due to heat convection.
Due to this internal motion, some of the plates are constantly sliding at the edges (more commonly) in relation to others. This kind of continuous movement detached one plate from other. The broken pieces of land masses then drifted away from each other and caused the division of the continents.
It is believed that the mountains were formed when one plate of the crust pushed itself against another and the resultant pressure thrust a part of the land upwards.
All the information about how was the Earth formed provided in this article is based upon various research studies conducted by geologists, cosmologists, etc. The changes that we have discussed here took place on the planet Earth gradually over a period of several millions of years.
The geological features of the Earth then provided a suitable condition for evolution of life on the planet which appeared within one billion years of its formation. However, the human species came into existence much later.