The Evolution Of The Atmosphere

Question 0

Describe phase 2 - green plants and oxygen

Answer 0

1. CO2 dissolved into oceans
2. Green plants evolved, removed CO2 added O2
3. O2 increased, CO2 locked up in fossil fuels
4. Nitrogen added to atmosphere from bacteria
5. Nitrogen not reactive, didn’t break down so built up

Question 1

Describe phase 1 - volcanoes

Answer 1

1. Earths surface was molten
2. Eventually cooled to give a crust, but volcanoes erupted releasing carbon dioxide, steam and ammonia
3. Atmosphere was formed of CO2 and water vapour

Question 2

Describe phase 3 - ozone layer and complex animals

Answer 2

1. O2 built up, allowing more complex organisms to develop
2. Ozone layer created (O3) blocking harmful rays from sun
3. Virtually no CO2 left

Question 3

What is the present composition of the atmosphere?

Answer 3

78% nitrogen, 21% oxygen, 0.035% carbon dioxide

+ water vapour + noble gasses (argon)