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AQA GCSE · Question 10.5 · Chemistry of the atmosphere
Why are scientists not certain about the percentage of each gas in the Earth's early atmosphere?
Why are scientists not certain about the percentage of each gas in the Earth's early atmosphere?
How to approach this question
Consider the timescale involved (billions of years). Were humans or scientific instruments around to take measurements of the early atmosphere? What does this mean for the evidence we have today?
Full Answer
There is a lack of direct evidence / no one was there to measure it.
Scientists are not certain about the exact composition of the Earth's early atmosphere because it formed about 4.6 billion years ago. There is no direct evidence from that time. No humans were present to record data, and no ancient air samples have been preserved. Scientists have built up a theory based on indirect evidence, such as analysing the gases released by volcanoes today, studying the atmospheres of other planets like Venus and Mars, and analysing ancient rocks. However, because this evidence is indirect, the conclusions remain theories with a degree of uncertainty.
Common mistakes
✗ Stating that the gases have changed, which is true but doesn't explain the uncertainty.
✗ Suggesting that the evidence is unreliable without explaining why (because it's indirect).
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