What were the gases which initially formed the earth’s atmosphere?

 Question.

What were the gases which initially formed the earth’s atmosphere? 

( NCERT, Class 11, Fundamentals of Physical geography)

Answer.

As we know that the present atmosphere mainly consists of nitrogen (78%) and Oxygen (21%). Initially, nitrogen and oxygen were not present in the atmosphere.

• The early atmosphere (about 4.6 billion years ago) consisted mainly of hydrogen and helium gases.
• After the full evolution of the Sun, solar winds blew hydrogen and helium out of Earth's atmosphere.
• During the Earth's cooling period, water vapor and other gases from the Earth's interior were released into the atmosphere. This was the beginning of the evolution of the current atmosphere and the process is also known as degassing.
• The early atmosphere consisted mainly of water vapor, nitrogen, carbon dioxide, methane, ammonia, and little free oxygen.
• After the cooling of the earth and degassing, the water vapor began to condense and the carbon dioxide present in the atmosphere dissolved in the rainwater. As carbon dioxide [a greenhouse gas] in the atmosphere decreases, the Earth's temperature drops further, which leads to accelerating the process of condensation and causing more precipitation.
• The ocean formed about 4 billion years ago. Oxygen began to flood into the atmosphere since the beginning of life, about 2.5 to 3 billion years ago.

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