!! 5.9.1

Question 1

how long has the proportions of earth’s atmosphere stayed the same

Answer 1

more or less 200 million years

Question 2

why is there limited evidence about earth’s early atmosphere and how it was formed

Answer 2

because of 4.6 million year time scale

Question 3

which gases are the earth’s atmosphere currently composed of

Answer 3

nitrogen (78%)

oxygen (21%)

small proportions of various other gases
including:

carbon dioxide

water vapour

noble gases

Question 4

what was Earth’s early atmosphere like

Answer 4

mostly carbon dioxide and water vapour

(released through intense volcanic activity)

little to no oxygen

small amounts of methane

Question 5

what is the volcanic theory of earths early atmosphere

Answer 5

suggests that during the first billion years of the Earth’s
existence there was intense volcanic activity

which released carbon dioxide and water vapour

volcanoes also produced nitrogen which gradually built up in
atmosphere

little to no oxygen

Question 6

what happened in the later part of earth’s atmosphere when earth cooled down

Answer 6

water vapour condensed into oceans

atmospheric amounts dropped

Question 7

what happened to carbon dioxide in the atmosphere when the oceans formed

Answer 7

dissolved in the water and carbonates were precipitated producing sediments,

reducing amount of co2 in atmosphere

Question 8

when did algae evolve

Answer 8

2.7 million years ago

Question 9

what happened to the atmosphere when algae evolved

Answer 9

Algae produced the oxygen that is now in the atmosphere by photosynthesis

over next billion years plants evolved

percentage of oxygen gradually increased to a level that enabled animals to evolve

co2 absorbed through photosynthesis

Question 10

How carbon dioxide levels decrease

Answer 10

by algae and plants through photosynthesis.

by the formation of sedimentary rocks and fossil fuels that contain carbon