AQA GCSE Combined Science (8464), Higher tier · Chemistry › Chemistry of the atmosphere › The composition and evolution of the Earth's atmosphere
Practise The Earth's early atmosphere. 14 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
One theory of how the Earth's first atmosphere and the oceans formed, what the early atmosphere contained, and why scientists cannot be certain about it. Expect recall and 'describe' questions, and questions where you use data you are given to interpret evidence and evaluate theories.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Say where the early atmosphere came fromIntense volcanic activity during the Earth's first billion years released the gases that formed it.
4
Name the main gas in the early atmosphereIt was mainly carbon dioxide with little or no oxygen, like the atmospheres of Mars and Venus today.
4
Describe how the oceans formedWater vapour released by volcanoes condensed to form the oceans.
5
Name other gases in the early atmosphereNitrogen from volcanoes gradually built up, and there may have been small proportions of methane and ammonia.
6
Explain how the oceans removed carbon dioxideCarbon dioxide dissolved in the oceans and carbonates were precipitated, forming sediments.
6
Explain why evidence about it is limitedThe time scale is about 4.6 billion years, so no one could measure it and little evidence survives.
7
Use given evidence to evaluate a theorySay which evidence supports the theory, which does not, and why the evidence is uncertain, then give a conclusion.
Notes
How the early atmosphere formed (one theory)
The Earth is about 4.6 billion years old.
One theory suggests that during the first billion years of the Earth's existence there was intense volcanic activity. The volcanoes released the gases that formed the early atmosphere.
Volcanoes also released water vapour, which condensed to form the oceans.
You only need to know this one theory, but you may be given information about others and asked to compare them.
What the early atmosphere contained
At the start of this period the atmosphere may have been like the atmospheres of Mars and Venus today: mainly carbon dioxide, with little or no oxygen.
Volcanoes also produced nitrogen, which gradually built up in the atmosphere.
There may also have been small proportions of methane, CH4, and ammonia, NH3.
The first fall in carbon dioxide
When the oceans formed, carbon dioxide dissolved in the water.
Carbonates were then precipitated (formed as insoluble solids) and settled to produce sediments.
This reduced the amount of carbon dioxide in the atmosphere.
Why scientists are not certain
Theories about the early atmosphere have changed and developed over time as new evidence has been found.
Evidence is limited because of the huge time scale of 4.6 billion years: no one was there to measure the atmosphere, and very little rock from that time survives unchanged.
Scientists rely on indirect evidence, such as the chemicals in very old rocks, the gases that volcanoes release today, and comparisons with other planets.
To evaluate a theory: say which evidence supports it, which evidence does not, and why the evidence is uncertain (for example, it is indirect or comes from only a few samples). Then give a conclusion. grade 7+
Cheatsheet
Age of the Earth: about 4.6 billion years
First billion years: intense volcanic activity released the gases
Early atmosphere: mainly carbon dioxide, little or no oxygen (like Mars and Venus today)
Also nitrogen (built up gradually), and maybe small proportions of methane and ammonia
Oceans: water vapour from volcanoes condensed
Carbon dioxide dissolved in the oceans → carbonates precipitated → sediments
Evidence is limited because of the time scale of 4.6 billion years
How to answer each type of question
Recall and describe: the early atmosphere and the oceans
1 to 3 marks4
Main gas: carbon dioxide. Where it came from: volcanoes.
For the oceans, give the source (water vapour from volcanoes) and the process (it condensed).
Example. (a) Name the main gas in the Earth's early atmosphere. (b) Describe how the oceans formed.
Show the model answer
(a) Carbon dioxide (1) (b) Volcanoes released water vapour (1), which condensed to form the oceans (1)
Explain how the oceans reduced carbon dioxide
2 marks6
Say that carbon dioxide dissolved in the ocean water.
Say that carbonates were precipitated and formed sediments, so the carbon was removed from the atmosphere.
Example. Explain how the formation of the oceans reduced the amount of carbon dioxide in the Earth's early atmosphere.
Show the model answer
Carbon dioxide from the atmosphere dissolved in the ocean water (1). Carbonates were precipitated and settled as sediments, so the carbon was locked away and not returned to the atmosphere (1).
Explain why evidence is limited
2 marks6
Link your answer to the time scale: about 4.6 billion years.
Give a second, different reason, e.g. no direct measurements, or little unchanged rock survives.
Example. Scientists are not certain what the Earth's early atmosphere contained. Give two reasons why.
Show the model answer
Any two from: it existed billions of years ago / about 4.6 billion years ago (1) no one was there to measure it / no samples of it exist (1) very little rock from that time survives unchanged, so there is little evidence (1)
Interpret evidence and evaluate a theory
3 to 4 marks7
Quote data from the table or text you are given.
Link each piece of data to a part of the theory it supports.
Give at least one limitation of the evidence.
Finish with a conclusion: does the evidence support the theory, and how strongly?
Example. The approximate percentages of the gases released by a volcano today are: water vapour 60%, carbon dioxide 25%, sulfur dioxide 10%, nitrogen 3%, other gases 2%. A scientist says this is evidence for the theory that the Earth's early atmosphere formed from volcanic gases. Evaluate the scientist's claim.
Show the model answer
Volcanoes release a large percentage of carbon dioxide (25%), which fits an early atmosphere that was mainly carbon dioxide (1). They release a lot of water vapour (60%), which could have condensed to form the oceans, leaving carbon dioxide as the main gas (1). They release nitrogen (3%), which could have built up gradually (1). However, volcanoes today may not release the same gases as volcanoes billions of years ago, so this evidence supports the theory but does not prove it (1).
Shortcuts and memory tricks
Story in one line: volcanoes → gases (mainly CO2) → water vapour condenses → oceans → CO2 dissolves → carbonate sediments.
Early Earth's air was like Mars and Venus today: mostly CO2, almost no O2.
Early gases: 'Cows Never Make Any Waves': Carbon dioxide (most), Nitrogen, Methane, Ammonia, Water vapour.
Why uncertain? Think TIME: 4.6 billion years ago, no one there to measure, rocks since changed.
Where marks are lost
Saying the early atmosphere was mainly oxygen or nitrogen. It was mainly carbon dioxide with little or no oxygen.
Saying the oceans formed from 'rain' without saying that water vapour from volcanoes condensed.
Saying carbon dioxide 'turned into' the oceans. It dissolved in the oceans, and carbonates were precipitated as sediments.
Giving vague reasons for uncertainty such as 'they don't know'. Say why: the time scale, no direct measurements, little evidence survives.
Getting the order wrong: volcanoes and carbon dioxide came first, and oxygen appeared only much later, after algae evolved.
Exam technique
When you are given data about Mars and Venus, or about volcanic gases, quote the numbers in your answer.
'Evaluate' means give evidence for and against, then a conclusion.
Use the key words examiners look for: volcanic activity, condensed, dissolved, precipitated, sediments.
Only one theory is on the specification, so answer using it unless the question gives you information about another.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Name the process that released most of the gases that formed the Earth's early atmosphere.
volcanic activity
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
The Earth is about 4.6 billion years old. One theory describes how the Earth's early atmosphere formed.
(a) According to this theory, what was the main gas in the Earth's early atmosphere? Tick (✓) one box.[1]
Argon
Carbon dioxide
Nitrogen
Oxygen
(b) Where did the gases in the early atmosphere come from?[1]
(c) How were the oceans formed?[1]
(d) Name two other gases that may have been in the early atmosphere in small proportions.[2]
Show the answer and mark scheme
(a)Answer: Carbon dioxide
(b)
volcanoes / volcanic activity
(c)
water vapour (from volcanoes) condensed
(d)
nitrogen
methane
ammonia
water vapour
Question 2Medium5 marks
During the first billion years of the Earth's existence there was intense volcanic activity.
(a) Describe how the oceans formed.[2]
(b) Explain how the formation of the oceans reduced the amount of carbon dioxide in the atmosphere.[2]
(c) Volcanoes also released nitrogen. The nitrogen gradually built up in the atmosphere. Suggest why the nitrogen built up rather than being removed from the atmosphere.[1]
Show the answer and mark scheme
(a)
volcanoes released water vapour
the water vapour condensed (as the Earth cooled)
(b)
carbon dioxide dissolved in the (ocean) water
carbonates were precipitated, producing sediments
(c)
nitrogen is unreactive / does not dissolve well in water (so it was not removed)
Question 3Hard6 marks
One theory suggests how the Earth's early atmosphere and oceans formed during the first billion years of the Earth's existence.
Describe this theory of how the Earth's early atmosphere and oceans formed. Explain how the amount of carbon dioxide in the early atmosphere then began to decrease.[6]
Show the answer and mark scheme
intense volcanic activity during the first billion years
volcanoes released gases that formed the early atmosphere
the early atmosphere was mainly carbon dioxide with little or no oxygen (like Mars and Venus today)
volcanoes also released nitrogen, which gradually built up; there may have been small proportions of methane and ammonia
water vapour released by volcanoes condensed to form the oceans
carbon dioxide dissolved in the oceans
carbonates were precipitated, producing sediments
this reduced the amount of carbon dioxide in the atmosphere
Marked with levels of response: the full level descriptors are in the app.