AQA GCSE Chemistry
AQA GCSE Chemistry 4.9.1 The Composition and Evolution of the Earth's Atmosphere Exam Questions
Free AQA GCSE Chemistry exam questions for 4.9.1 The Composition and Evolution of the Earth's Atmosphere, with a mark scheme for every pack. Covers the proportions of gases in today's atmosphere, the early atmosphere, how oxygen increased and how carbon dioxide decreased.
4.9.1 The Composition and Evolution of the Earth's Atmosphere exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Chemistry 4.9.1 The Composition and Evolution of the Earth's Atmosphere
AQA GCSE Chemistry 4.9.1 tells the story of how the Earth's atmosphere developed over billions of years. You learn its composition today, one theory for the early atmosphere produced by volcanic activity, and the processes that increased oxygen and reduced carbon dioxide. The topic is assessed on Paper 2 in section 4.9 Chemistry of the atmosphere and links to greenhouse gases in 4.9.2 and carbon compounds in 4.7. Examiners ask you to interpret evidence, recognise that evidence is limited because of the timescales involved, and explain each change with a named process such as photosynthesis or the formation of sedimentary rocks.
What you need to know
- Today's atmosphere For about the last 200 million years the proportions of gases have been much the same: about four-fifths (approximately 80%) nitrogen, about one-fifth (approximately 20%) oxygen, and small amounts of other gases including carbon dioxide, water vapour and noble gases.
- The early atmosphere In the first billion years, intense volcanic activity released gases forming an atmosphere that was 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. Water vapour condensed to form the oceans.
- Reducing carbon dioxide Carbon dioxide dissolved in the oceans, and carbonate compounds precipitated to form sediments. Algae and plants then used carbon dioxide in photosynthesis. Carbon was locked into sedimentary rocks such as limestone and into fossil fuels (coal, crude oil and natural gas).
- Increasing oxygen Algae first produced oxygen about 2.7 billion years ago. Over the next billion years plants evolved and oxygen gradually increased, allowing animals to evolve. Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2.
- Evidence Evidence for the early atmosphere is limited because of the very long timescale (about 4.6 billion years), so theories have changed as new evidence is found.
Common mistakes in 4.9.1 The Composition and Evolution of the Earth's Atmosphere
- Saying the early atmosphere was mostly nitrogen or oxygen. It was mainly carbon dioxide with little or no oxygen.
- Saying oxygen in today's air is about 80%. Nitrogen is about 80% and oxygen about 20%.
- Giving only 'plants' for removing carbon dioxide. Also mention dissolving in oceans, forming carbonate rocks and fossil fuels.
- Forgetting that oceans formed from condensing water vapour as the Earth cooled.
- Presenting the theory as certain. Explain that evidence is limited.
Try three 4.9.1 The Composition and Evolution of the Earth's Atmosphere exam-style questions
1. Give the approximate percentages of nitrogen and oxygen in the atmosphere today. (2 marks)
Show the mark scheme answer
Nitrogen about 80% (four-fifths); oxygen about 20% (one-fifth).
2. Describe how the amount of carbon dioxide in the early atmosphere decreased. (4 marks)
Show the mark scheme answer
Carbon dioxide dissolved in the oceans; carbonates precipitated forming sediments; algae and plants absorbed carbon dioxide by photosynthesis; carbon locked into sedimentary rocks (limestone) and fossil fuels.
3. Explain why scientists are not certain about the composition of Earth's early atmosphere. (2 marks)
Show the mark scheme answer
It formed about 4.6 billion years ago, a very long time; so there is little direct evidence, no one could measure it.
4.9.1 The Composition and Evolution of the Earth's Atmosphere FAQs
What does AQA GCSE Chemistry 4.9.1 cover?
It covers the composition of today's atmosphere, a theory of the early atmosphere from volcanic activity, how oxygen increased and how carbon dioxide decreased.
Which paper is 4.9.1 on?
Section 4.9 Chemistry of the atmosphere is assessed on AQA GCSE Chemistry Paper 2.
How do I structure a 6 mark answer on the evolution of the atmosphere?
Work in time order: volcanoes and the early carbon dioxide atmosphere, oceans forming, carbon dioxide dissolving and forming carbonates, photosynthesis increasing oxygen, then carbon locked in rocks and fossil fuels. Link each change to a named process.
