High Frequency
What Examiners Ask About Atmosphere Composition
- "State the approximate proportions of nitrogen and oxygen in the atmosphere" — 78% nitrogen, 21% oxygen (1 mark)
- "Describe how the atmosphere changed from Earth's early history to today" — decrease in CO₂, increase in O₂ due to photosynthesis (3–4 marks)
- "Explain how photosynthesis changed the atmosphere" — plants removed CO₂, released O₂ (2–3 marks)
- "Why is there evidence that the early atmosphere had high CO₂ levels?" — limestone deposits, comparison with Venus/Mars (2 marks)
- "Give two ways CO₂ was removed from the early atmosphere" — dissolved in oceans/photosynthesis (2 marks)
Edexcel 1CH0: Examined in Paper 2 (1CH0/2). Edexcel tests the evolution of the Earth's atmosphere over billions of years — you must explain why oxygen levels increased and carbon dioxide levels decreased. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.
This exam focus covers Exam Focus within Composition of Atmosphere for GCSE Chemistry. Revise Composition of Atmosphere in Atmosphere for GCSE Chemistry with 20 exam-style questions and 12 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Composition of Atmosphere
What is the approximate percentage of nitrogen in the current atmosphere?
Describe how Earth's early atmosphere was formed.