The atmosphere
AQA GCSE Chemistry revision on The atmosphere. Aligned to the AQA GCSE Chemistry 8462 specification. This bank has 8 practice questions on this topic.
Sample questions (3 of 8)
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Question 1
Today's atmosphere is roughly ___ nitrogen and ___ oxygen.
- A) 50% / 50%
- B) 78% / 21%
- C) 21% / 78%
- D) 90% / 10%
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Answer: 78% / 21%
Composition: nitrogen 78%, oxygen 21%, argon ~1%, carbon dioxide ~0.04%, plus traces of water vapour, methane, etc. CO2 is small but mighty for climate - it's risen from 280 ppm (pre-industrial) to ~420 ppm today. Oxygen levels stay roughly constant - balanced by photosynthesis (in) and respiration + combustion (out).
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Question 2
Greenhouse gases trap heat in the atmosphere by...
- A) Reflecting heat back to the Sun
- B) Absorbing outgoing infrared radiation + re-emitting some downward
- C) Cooling the air
- D) Generating electricity
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Answer: Absorbing outgoing infrared radiation + re-emitting some downward
Sunlight (visible) passes through the atmosphere, warms the Earth. Earth re-emits energy as INFRARED. Greenhouse gases (CO2, CH4, H2O vapour, N2O) absorb infrared and re-radiate it in random directions - some back to Earth's surface. Without ANY greenhouse effect, Earth would average -18C. Natural effect keeps us at +14C. EXTRA greenhouse gases from human activity = +1.2C above pre-industrial + rising.
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Question 3
The early atmosphere (~4 billion years ago) was probably formed by...
- A) Photosynthesis
- B) Volcanic activity releasing CO2, water vapour and other gases
- C) Asteroids only
- D) Plant respiration
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Answer: Volcanic activity releasing CO2, water vapour and other gases
Early Earth: lots of volcanic activity. Released gases formed primitive atmosphere: mostly CO2, water vapour, nitrogen, with traces of methane + ammonia. NO oxygen. As Earth cooled, water vapour condensed -> oceans. Most CO2 dissolved in oceans + locked in carbonate rocks (limestone). Oxygen only appeared once cyanobacteria (~2.4 billion years ago) started photosynthesising - the 'Great Oxidation Event'.
Want to test yourself on the remaining cards for this topic?
5 more questions on The atmosphere — plus mistakes tracking and spaced repetition across the whole Chemistry spec.