Earth's Atmosphere Composition Chapter 8

Composition of Earth's Atmosphere

• The present atmosphere is mainly composed of nitrogen and oxygen.

Evolution of the Present Atmosphere

• The process of evolution of the present atmosphere can be divided into three stages.
• The first stage involved the loss of the primordial atmosphere due to solar winds.

Loss of Primordial Atmosphere

• The early atmosphere, composed of hydrogen and helium, was stripped off due to solar winds.
• This phenomenon occurred not only on Earth but also on other terrestrial planets.

Second Stage of Evolution

• The hot interior of the Earth contributed to the evolution of the atmosphere during the cooling process.
• Gases and water vapour were released from the interior of the solid Earth through a process called degassing.
• Volcanic eruptions also contributed to the release of gases and water vapour into the atmosphere.

Formation of Oceans

• The released water vapour condensed and fell onto the surface, collecting in depressions to form oceans.
• The oceans were formed within 500 million years of the Earth's formation, making them approximately 4,000 million years old.

Emergence of Life

• Life began to evolve around 3,800 million years ago.
• The process of photosynthesis emerged around 2,500-3,000 million years ago.
• Initially, life was confined to the oceans, with oxygen being released into the oceans through photosynthesis.
• Eventually, the oceans became saturated with oxygen, and around 2,000 million years ago, oxygen began to flood the atmosphere.