C9 - The Evolution of the Atmosphere

Phase 1:

The surface was covered in volcanoes that erupted and released gases. This was likely how the early atmosphere was formed.

The early atmosphere was probably mostly carbon dioxide, with virtually no oxygen, similar to Mars and Venus today.

Volcanic activity released nitrogen, which built up in the atmosphere over time, as well as water vapour and small amounts of methane and ammonia. 

Phase 2:

Water vapour condensed, forming oceans.

Lots of carbon dioxide was removed as it dissolved in oceans. The dissolved carbon dioxide went through a series of reactions to form carbon precipitates that formed sediments on the sea bed. 

Green plats and algae evolved and absorbed some carbon dioxide to carry out phtotosynthesis. Later, marine animals evolved - their shells and skeletons contained carbonates from the oceans.

Some of the carbon these organisms took in from the atmosphere and oceans became locked up in rocks and fossil fuels after the organisms died. 

Phase 3:

Green plants and algae also produced oxygen by photosynthesis.

Algae evolved first - about 2.7 billion years ago. Over the next billion years or so, green plants evolved. 

As oxygen levels built up in the atmosphere over time, more complex life (like animals) could evolve.

Eventually, about 200 million years ago, the atmosphere reached a composition similar to today: approximately 80% nitrogen, 20% oxygen and small amounts of other gases (each making up less than 1% of the atmosphere), mainly carbon dioxide, noble gases and water vapour.