AtmosphereTopic Summary
Topic Summary: Atmosphere Composition
Part of Composition of Atmosphere — GCSE Chemistry
This topic summary covers Topic Summary: Atmosphere Composition 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 less often, but it can still be a useful differentiator on mixed-topic papers. It is section 13 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 13 of 13
Practice
20 questions
Recall
12 flashcards
Topic Summary: Atmosphere Composition
Current Atmosphere
- 78% Nitrogen (N₂)
- 21% Oxygen (O₂)
- ~1% Argon (Ar)
- 0.04% Carbon dioxide (CO₂)
Early Atmosphere
- Mainly CO₂ and water vapour
- Some N₂, CH₄, NH₃
- Little/no oxygen
- Like Venus and Mars today
How CO₂ Decreased
- Dissolved in oceans
- Formed carbonate rocks (limestone)
- Photosynthesis by cyanobacteria
- Buried as fossil fuels
How O₂ Increased
- Cyanobacteria evolved ~3.5 billion years ago
- Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- Plants continued the process
- Now balanced by respiration