AQA GCSE Chemistry Foundation (8462), Foundation tier · Chemistry of the atmosphere › Composition and evolution of the atmosphere
Practise The Earth's early atmosphere. 8 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.
Key facts
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
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
diagram
When the oceans formed, carbon dioxide dissolved in the water.
Carbonates were then precipitated (formed as insoluble solids) and settled to produce sediments.
Volcanic gases formed the early atmosphere; the oceans then took up some carbon dioxide.
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.
How to answer each type of question
Recall and describe: the early atmosphere and the oceans
1 to 3 marksGrade 4
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 answerHide the model answer
(a) Carbon dioxide (1) (b) Volcanoes released water vapour (1), which condensed to form the oceans (1)
Don’t lose marks
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.
More tips
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.
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.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Say where the early atmosphere came fromIntense volcanic activity during the Earth's first billion years released the gases that formed it.
Grade 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.
Grade 4
Describe how the oceans formedWater vapour released by volcanoes condensed to form the oceans.
Grade 5
Name other gases in the early atmosphereNitrogen from volcanoes gradually built up, and there may have been small proportions of methane and ammonia.
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)