composition & evolution of atmosphere

Question 1

how long ago did the atmosphere reach a similar composition to today?

Answer 1

200 million years

Question 2

state the proportions of gases in todays atmosphere

Answer 2

• 78% nitrogen
• 21% oxygen
• 0.9% other incl. water vapour, methane
• 0.03% carbon dioxide

Question 3

describe how the carbon dioxide level has increased recently

Answer 3

• past 100-200 years increase
• due to industrial revolution
• human activity
• burning of fossil fuels

Question 4

why is this just a theory?

Answer 4

evidence is limited because of the time scale of 4.6 billion years

Question 5

what was the early atmosphere similar to?

Answer 5

the current atmospheres of mars and venus, consisting of mainly carbon dioxide with little to no oxygen

Question 6

first stage

Answer 6

• first billion years of earth’s history, the surface was covered in volcanoes
• this is how early atmosphere was formed
• CO2 levels increased due to intense volcanic activity, and mostly made up the atmosphere
• volcanic activity also released nitrogen, water vapour and small amounts of methane and ammonia

Question 7

stage two

Answer 7

• 4.4 to 2.7 billion years ago carbon dioxide levels decreased because water vapour condensed to form oceans, when the earth’s temperature cooled to below 100°C
• carbon dioxide dissolved in oceans and carbonates were precipitated producing sediments
• sedimentary rocks formed
• reducing amount of co2 in atmosphere

Question 8

what was the early atmosphere like and why?

Answer 8

• mostly carbon dioxide, with little to no oxygen gas
• due to intense volcanic activity which released carbon dioxide, as well as a small number of other gases

Question 9

stage 3

Answer 9

• 2.7 - 1.7 billion years ago, oxygen levels increased and carbon dioxide levels decreased
• due to algae appearing and plants evolving
• algae evolved first 2.7 billion years ago
• green plants evolved over the next 1 billion year
• because algae and plants photosynthesise, taking in and absorbing carbon dioxide and releasing oxygen
• as oxygen levels built up it meant animals could evolve
• carbon dioxide levels also decreased by the formation of sedimentary rocks and fossil fuels, containing carbon

Question 10

describe how carbon is trapped in fossil fuels and rocks

Answer 10

• when plants, plankton and marine animals die they fall to the seabed and get buried by layers of sediment
• over millions of years, they become compressed and form sedimentary rocks, oil and gas, trapping the carbon within them

Question 11

describe how crude oil and natural gases are formed

Answer 11

• formed from deposits of plankton
• these fossil fuels form reservoirs under the seabed when they get trapped in rocks

Question 12

describe how coal is formed

Answer 12

coal is a sedimentary rock made from thick plant deposits

Question 13

describe how limestone is formed

Answer 13

limestone is a sedimentary rock mostly made of calcium carbonate deposits from the shells and skeletons of marine organisms