#170
4.9.1.4 How carbon dioxide decreased
Paper 2 · Higher combined
Spec reference: 4.9.1.4 (under 4.9.1).
What you need to know
- (Key facts / definitions / equations for this spec point)
Support videos
- FreeScienceLessons (topic playlist): (use links below)
- PMT videos hub (Atmosphere): https://www.physicsandmathstutor.com/chemistry-revision/gcse-aqa/chemistry-of-atmosphere/
Self-assessment (checklist)
- I can explain why evidence for the early atmosphere is
- I can name the types of organisms that carry out
- I can write a word equation to represent
- I can write a symbol equation to represent
- I can describe how the percentage of oxygen in the
- I can recall how many years ago oxygen first appeared
- I can describe how the percentage of carbon dioxide
- I can describe the main changes in the atmosphere
Key steps (method)
- Identify what the question is testing and use precise chemistry vocabulary.
- If it’s a calculation: write the equation/formula first, then substitute carefully.
Common mistakes
- Missing units/state symbols when asked.
- Giving a statement without linking cause → effect.
Exam-style questions (quick)
- Define the key term(s) for this point in the spec.
- Explain a typical property/result using particle/bonding ideas.
- Do a short calculation or interpretation step relevant to this point.
Practice questions
- PMT: Atmosphere (questions + notes): https://www.physicsandmathstutor.com/chemistry-revision/gcse-aqa/chemistry-of-atmosphere/