Topic 8) The evolution of the atmosphere

Question 1

how long ago did the earth form?

Answer 1

4.6 billion years ago

Question 2

what is the composition of the atmosphere?

Answer 2

78% nitrogen, 21% oxygen, 1% argon, <1% all other gases

Question 3

what are the 3 main stages of the evolution of earths atmosphere?

Answer 3

phase 1 - volcanoes emitted large amounts of gas
phase 2 - earth cooled, oceans formed, plants and algae evolved
phase 3 - plants and algae produced oxygen, eventually forming the atmosphere we have today

Question 4

what happened to earth’s atmosphere in the first billion years?

Answer 4

earths surface was very volcanic, releasing lots of carbon dioxide and nitrogen

Question 5

how were oceans formed?

Answer 5

after 1 billion years, the earth cooled, causing water vapour in the atmosphere to condense into liquid and form the oceans

Question 6

what happened to most of the carbon dioxide in the early atmosphere?

Answer 6

dissolved into the oceans
dissolved CO2 form carbonate precipitates
these form sediments on the sea bed

Question 7

what is limestone made of?

Answer 7

calcium carbonate deposits from the shells and skeletons of marine organisms

Question 8

when did algae start producing oxygen?

Answer 8

2.7 billion years ago