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C9: History of the Atmosphere - Coggle Diagram
C9: History of the Atmosphere
Oxygen in the Atmosphere
Life was first formed on Earth around 3.4 billion years ago.
The organisms formed were simple, and similar to bacteria.
They used the breakdown of chemicals as an energy source.
Around 2.7 billion years ago, simple organisms, like algae, evolved.
Algae evolved to use energy from the sun to make their own food, through the process of photosynthesis.
The process of photosynthesis produces oxygen as a waste product, and this is the first instance of oxygen in the Earth's atmosphere.
Over the next billion years, oxygen levels rose as algae and bacteria photosynthesised more.
More plants evolved, and since they were are all photosynthesising, oxygen was made, and carbon dioxide was used up.
Current Oxygen Levels in the atmosphere are around 20%
Formation of the Atmosphere
There were hollows in the crust as it formed & solidified, which water fell into to form the first oceans.
Comets could have also added water to the earth, speculating that icy comets could rain on the Earth as they melted.
These three gases formed the early atmosphere, and water vapour cooled to fall as rain.
The atmosphere was mostly carbon dioxide as the planet stabilised.
It is thought that volcanoes produced carbon dioxide, water vapour and nitrogen
There could have also been water vapour, nitrogen and small traces of methane and ammonia.
There was very little oxygen at the beginning of the atmosphere.
This is very similar to the modern day atmospheres on Mars and Venus.
After the carbon dioxide heavy atmosphere formed, there were little to no changes until the formation of life (see Oxygen in the Atmosphere & Change in the Atmosphere).
How We Know
Scientists gathered data by studying gas bubbles in ancient rocks.
They also gathered data from other planets and their moons.
There is little direct evidence because the earth and its atmosphere formed billions of years ago.
Change in the Atmosphere
The composition of the early atmosphere was mostly carbon dioxide, with significant amounts of water vapour and nitrogen, but no oxygen.
As shown in Oxygen in the Atmosphere, the presence of photosynthesisers increased the oxygen levels.
The atmosphere first began to change around the time that photosynthesisers evolved, due to the fact that they produced oxygen as a waste product.
Many of the micro-organisms that lived in the early atmosphere died out because they could not survive in an oxygen-rich atmosphere.