AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The proportions of different gases in the atmosphere: For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:
For about 200 million years the atmosphere has been stable in composition, and it is still roughly the same today.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
For about 200 million years the atmosphere has been stable in composition, and it is still roughly the same today. The main gases are nitrogen, about 78% of the atmosphere, and oxygen, about 21%. The remaining 1% is mostly argon, with small and variable amounts of carbon dioxide, water vapour and other noble gases. These proportions are approximate because water vapour varies with location and weather, and carbon dioxide has risen slightly since industrialisation. The early atmosphere was very different, formed mainly by volcanic activity and containing little or no oxygen, so the current stability is the result of long-term processes such as photosynthesis.
What earns the marks
- Nitrogen makes up about 78% of the atmosphere.
- Oxygen makes up about 21% of the atmosphere.
- Argon is the next most abundant gas at roughly 0.9%, so the remaining 1% is mainly argon.
- Carbon dioxide is a trace gas, currently around 0.04%, and water vapour is variable.
- The composition has been approximately constant for 200 million years, but the early atmosphere was different.
- Percentages are approximate and should be quoted to sensible values, not as exact fixed numbers.
Common mistakes and how to put them right
Reversing nitrogen and oxygen percentages.
Put it right: Nitrogen is about 78% and oxygen about 21%.
Saying carbon dioxide is a major component.
Put it right: It is a trace gas, roughly 0.04%.
Treating the 1% as entirely carbon dioxide.
Put it right: It is mostly argon, with carbon dioxide and other trace gases.
Describing the atmosphere as unchanging since Earth formed.
Put it right: It has been stable for about 200 million years, but the early atmosphere was very different.
Exam tips
- Learn the two main percentages as 78% nitrogen and 21% oxygen, and remember the remaining 1% is mostly argon.
- If asked to compare with the early atmosphere, mention high carbon dioxide and little or no oxygen.
- Use approximate language such as about or roughly, because the values are not exact.
- Check whether the question asks for percentages or fractions before writing your answer.
Try the lesson
The start of the The proportions of different gases in the atmosphere: For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today: lesson, made from checked teaching notes for this specification point.
Have a go first
For the last 200 million years, the proportions of gases in the atmosphere have stayed much the same. Which gas makes up about four-fifths of the atmosphere today?
Listen
For about 200 million years the atmosphere has been stable in composition, and it is still roughly the same today. The main gases are nitrogen, about 78% of the atmosphere, and oxygen, about 21%. The remaining 1% is mostly argon, with small and variable amounts of carbon dioxide, water vapour and other noble gases. These proportions are approximate because water vapour varies with location and weather, and carbon dioxide has risen slightly since industrialisation. The early atmosphere was very different, formed mainly by volcanic activity and containing little or no oxygen, so the current stability is the result of long-term processes such as photosynthesis. A strong answer earns marks for these points. Nitrogen makes up about 78% of the atmosphere. Oxygen makes up about 21% of the atmosphere. Argon is the next most abundant gas at roughly 0.9%, so the remaining 1% is mainly argon. Carbon dioxide is a trace gas, currently around 0.04%, and water vapour is variable. A common slip: Reversing nitrogen and oxygen percentages. Instead, nitrogen is about 78% and oxygen about 21%. Exam tip: Learn the two main percentages as 78% nitrogen and 21% oxygen, and remember the remaining 1% is mostly argon.
Key words
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Atmospheric composition
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Long-term stability
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Trace gases and variability
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Contrast with the early atmosphere
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See every definition
- Atmospheric composition
- The proportions of different gases in the atmosphere, with nitrogen about 78% and oxygen about 21%.
- Long-term stability
- For 200 million years the proportions of different gases have been much the same as they are today.
- Trace gases and variability
- The remaining 1% is mostly argon, with small and variable amounts of carbon dioxide, water vapour and other noble gases.
- Contrast with the early atmosphere
- The early atmosphere was very different, formed mainly by volcanic activity and containing little or no oxygen.
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