The earth is the only planet in our solar system which supports and hosts different life forms. It has a unique atmosphere. The oxygen present in the atmosphere helps to sustain life on earth.
According to an article published in theconversation.com, the earth once had a totally different atmosphere. Antony Burnham, a research fellow at Research School of Earth Sciences, and Hugh O'Neill, professor of Earth Sciences from the Australian National University offered detailed information about the ancient earth atmosphere and how it became the present-day atmosphere that can support life on earth. Their research paper was published in scienceAdvanced.org
As per the sources of theconversation.com, scientists found that the ancient earth’s atmosphere was quite similar to the atmosphere of Venus. They tried to recreate the chemical composition of the boiling magma oceans of the earth, which was present nearly billions of years ago. Then they studied deeper and conducted more experiments to check the nature of the atmosphere the lava ocean could form. Their research formed that the earth's initial atmosphere was a thick and toxic atmosphere comprising carbon dioxide and nitrogen. It is similar to the atmosphere of Venus at present.
As per the sources of space.com, the earth was initially hit by a large space object which caused the formation of the moon. This impact also caused the earth's surface to be covered by a boiling ocean of magma. The scientists assume that the magma gradually releases gases like hydrogen, carbon, oxygen, and nitrogen gases. These formed the first-ever atmosphere of the earth.
There was a small amount of oxygen, and other gases were more common. This atmosphere is quite similar to the present atmosphere of Venus, which is another planet of the solar system. Strikingly enough, the ratio of carbon dioxide to nitrogen gas of the earth's initial atmosphere is similar to Venus' atmosphere.
With time, the magma ocean of the earth cooled down and started to form a rocky crust. This cooling helped to condense the abundant water vapour. The oxygen which was present in the magma and bonded with iron was gradually released into the atmosphere. Hence, the atmosphere became rich with oxygen, and it was enough to sustain the primordial life on earth.