Earth’s Atmosphere

Question 1

Earth’s current atmosphere (dry air)

Answer 1

79% nitrogen
20% oxygen
<1% other gases (CO2, argon)

Question 2

How has earth’s atmosphere changed?

Answer 2

Earth’s early atmosphere was formed by volcanic activity so was extremely hot and consisted of mainly CO2 and some water vapour. As the earth cooled down, the water vapour condensed and formed the oceans. CO2 dissolved into the oceans and was taken in by organisms (eventually locked up in sedimentary rocks and fossil fuels). As plants evolved, photosynthesis took in CO2 and released O2. Methane and ammonia levels decreased as they reacted with oxygen but nitrogen is very unreactive so built up over time