The Earth's Early Atmosphere
Recap The Earth's Early Atmosphere for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. The Earth's early atmosphere was mostly carbon dioxide from volcanoes with little or no oxygen, similar to Mars and Venus today.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
For about 200 million years, the proportions of gases in the atmosphere have been much the same as they are today: approximately four fifths nitrogen and one fifth oxygen, with small proportions of other gases.
Evidence for the Earth's early atmosphere is limited, so theories about it have changed and there is much uncertainty. One widely accepted theory is that during the first billion years intense volcanic activity released gases that formed the early atmosphere, and water vapour that condensed to form the oceans.
The early atmosphere may have been mainly carbon dioxide, with little or no oxygen — similar to the atmospheres of Mars and Venus today. Volcanoes also produced nitrogen, which gradually built up, and small amounts of methane and ammonia.
Revision notes
The atmosphere today
For about 200 million years the proportions have been roughly constant.
Approximately four fifths, or 80 per cent, nitrogen and one fifth, or 20 per cent, oxygen, with small proportions of other gases including carbon dioxide, water vapour and noble gases.
The early atmosphere
During the first billion years there was intense volcanic activity, releasing gases that formed the early atmosphere.
It may have been mainly carbon dioxide with little or no oxygen, similar to Mars and Venus today. Volcanoes also produced nitrogen, and small amounts of methane and ammonia.
Why there is uncertainty
Evidence for the early atmosphere is limited because it was so long ago.
Theories have changed over time and there is much uncertainty. Questions often ask you to explain this, and the answer is the scarcity of direct evidence.
Key points
- The atmosphere is about 80 per cent nitrogen.
- It is about 20 per cent oxygen.
- Proportions have been constant for 200 million years.
- Volcanic activity formed the early atmosphere.
- The early atmosphere was mainly carbon dioxide.
- Evidence is limited so theories have changed.
Worked examples
Example 1
State the approximate proportions of nitrogen and oxygen in the atmosphere today. [2 marks]
Model answer
About four fifths, or 80 per cent, nitrogen (1 mark) and about one fifth, or 20 per cent, oxygen (1 mark).
Example 2
Describe how the Earth's early atmosphere is thought to have formed. [2 marks]
Model answer
Intense volcanic activity during the Earth's first billion years released gases (1 mark), which formed the early atmosphere and released water vapour that condensed to form the oceans (1 mark).
Example 3
Explain why scientists are uncertain about the composition of the early atmosphere. [2 marks]
Model answer
Evidence for conditions billions of years ago is very limited (1 mark), so theories are based on incomplete information and have changed as new evidence has emerged (1 mark).
Common mistakes
Giving oxygen as the main gas in the early atmosphere.
It was mainly carbon dioxide with little or no oxygen.
Saying the proportions have always been the same.
They have been roughly constant only for the last 200 million years.
Forgetting the uncertainty.
Limited evidence is a required point and often carries a mark.
Giving exact percentages.
Approximate values are expected: about 80 per cent and about 20 per cent.
Exam tips
- Learn the modern proportions as fractions and percentages.
- Name volcanic activity as the source of the early atmosphere.
- Always mention the limited evidence when explaining uncertainty.
- Compare with Mars and Venus if asked for supporting evidence.
Key terms
- Atmosphere
- The layer of gases surrounding the Earth.
- Volcanic activity
- The process that released gases forming the early atmosphere.
- Water vapour
- The gas that condensed to form the oceans.
- Uncertainty
- Doubt arising from limited evidence.
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Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.