C9: Evolution Of The Atmosphere

Question 1

Explain phase 1: volcanoes gave out gases.

Answer 1

Surface covered in volcanoes - released gases that formed the early atmosphere - carbon dioxide & virtually no oxygen (like Venus and mars today), nitrogen, water vapour, ammonia

Question 2

Explain phase 2: oceans, algae and green plants absorbed carbon dioxide.

Answer 2

The water vapour condensed forming the oceans
CO2 was removed as it dissolved in the oceans - the dissolved CO2 went through series of reactions to form carbonate precipitates that formed sediments on sea bed
Green plants & algae evolved to absorb CO2 through photosynthesis
Some of these carbon organisms became locked in rocks and fossil fuels after the organisms died

Question 3

Explain phase 3: green plants and algae produced oxygen.

Answer 3

Produced through photosynthesis
Algae evolved first (2.7 billion yrs ago)
Over next billion years green plants evolved
As oxygen levels built, more complex life could evolve
About 200 million yrs ago, the atmosphere reached a composition similar to today’s: approx. 80% nitrogen, 20% oxygen & small amounts of other gases like CO2, noble gases and water vapour