evolution of the atmosphere (topic 9) Flashcards
main gases in air from earths atmosphere today
- nitrogen: 78%
- argon: 1%
- oxygen: 21%
the percentages of carbon dioxide and oxygen have changed from Earth’s early atmosphere to Earth’s atmosphere today, explain the processes that led to these changes (6)
- carbon dioxide has decreased
- oxygen has increased
~~~~~~~~~~ - volcanic activity released water vapour
- the water vapour condensed to form oceans
~~~~~~~~~~ - carbon dioxide dissolved in oceans
- carbonates produce sediments
- carbon locked up in sedimentary rocks
- carbon locked up in fossil fuels
~~~~~~~~~~ - algae and plants evolved
- algae and plants absorbed carbon dioxide
- by photosynthesis
- which also released oxygen
where is it likely that the carbon dioxide in the early atmosphere came from (1)
volcanoes
state two differences between the atmosphere today and the atmosphere of billions of years ago (2)
- amount of CO2 is much lower
- amount of O2 is much higher
- amount of N2 is much higher
- less other gases
describe the processes which have brought about the changes in the proportions of gases in the air (6)
increase in oxygen:
- plants evolved
- plants and algae photosynthesise
- plants and algae give out O2
decrease in carbon dioxide:
- less CO2 is produced now from volcanic activity
- CO2 from air trapped in sedimentary rocks and fossil fuels
- CO2 is used by plants for photosynthesis
increase in nitrogen:
- nitrogen is produced by bacteria during the decay of dead organisms
- nitrogen is produced by reaction of NH3 with O2
- nitrogen builds up because it is unreactive
why are scientists not certain about the percentage of each gas in the earths early atmosphere (1)
- it occurred 4.6 billion years ago
- there is very limited evidence
describe and explain how the composition of the earths atmosphere was changed by the formation of coal (3)
- carbon dioxide decreased by plants
- oxygen increased by plants
- because coal stores carbon
at what temperature would oceans have started to form
100 degrees
describe how volcanoes caused the oceans to be formed (2)
- water vapour given out from volcano
- condensed
give two reasons why the percentage of carbon dioxide in the Earth’s atmosphere has decreased (2)
- used by green plants and algae
- plants take in carbon dioxide during photosynthesis
- dissolved in oceans / seas, absorbed in oceans
- locked up in fossil fuels
explain how carbon dioxide is released from limestone (2)
- calcium carbonate
- decomposed
suggest one reason why there was no liquid water on the Earth’s surface billions of years ago
the Earth’s surface temperature was above the boiling point of water
describe and explain how the surface of the early Earth and its atmosphere have changed to form the surface of the Earth and its atmosphere today (6)
change in carbon dioxide concentration:
- carbon dioxide decreased because plants and algae developed and used carbon dioxide for photosynthesis
- carbon dioxide decreased because oceans formed and dissolved carbon dioxide
- carbon dioxide became locked up in sedimentary rocks and fossil fuels
change in oxygen concentration:
- oxygen increased because plants and algae produce and release oxygen during photosynthesis
change in nitrogen concentration:
- nitrogen has formed because ammonia in the Earth’s early atmosphere reacted with oxygen
other changes:
- oceans formed because the Earth cooled and water vapour in the atmosphere condensed
- continents formed because the Earth cooled forming a supercontinent which formed the separate continents
- number of volcanoes decreased because the Earth cooled forming a crust
describe how carbon dioxide helps to maintain temperatures on earth (3)
- carbon dioxide allows short wavelength radiation to pass through
- the atmosphere to the earths surface
- carbon dioxide absorbs outgoing long wavelength radiation
exaplain why the percentage of nitrogen increased
because of intense volcanic activity
when it rains on Titan, it rains methane, use the information above to explain why (2)
- because methane’s boiling point is greater than the average surface temperature
- or titan’s average surface temperature is below methane’s boiling point
- any methane that evaporates will condense
some scientists think that living organisms could have evolved on Titan, explain why these organisms could not have evolved in the same way that life is thought to have evolved on Earth (3)
- titan has no oxygen
- so photosynthesis has not occurred on Titan
- therefore no carbon dioxide present on Titan
- or therefore oxygen using animals cannot have evolved on Titan
