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Cognito · AQA Chemistry Greenhouse effect and climate change
Key facts
Composition of modern atmosphere Nitrogen: ~78% . Oxygen: ~21%. Argon: ~0.9%. CO₂: ~0.04%. Trace gases.The atmosphere has been relatively stable for ~200 million years. Development of Earth's early atmosphere 1. Volcanic outgassing — early Earth had intense volcanic activity releasing: CO₂, water vapour, nitrogen, ammonia, methane. Very little oxygen.2. Cooling and oceans — as Earth cooled, water vapour condensed to form the oceans. CO₂ dissolved in the oceans.3. Photosynthesis — early algae and plants used CO₂ for photosynthesis, releasing O₂. Oxygen levels rose over billions of years.4. Current atmosphere — formed over ~3–4 billion years.Greenhouse gases and climate change Greenhouse gases : CO₂, methane, water vapour. They absorb and re-emit infrared radiation, warming Earth.Increasing CO₂ (burning fossil fuels, deforestation) → enhanced greenhouse effect → global warming. Climate change effects: sea level rise (ice melt), extreme weather, ecosystem disruption. Atmospheric pollutants : CO (toxic, from incomplete combustion), particulates (from diesel engines — cause respiratory disease and global dimming), sulfur dioxide (acid rain), nitrogen oxides (acid rain, photochemical smog).Carbon capture and storage (CCS) — capturing CO₂ from power stations and pumping it underground.Exam questions — 4 questions · 10 marks
⚡ Extended questions included. Read the hint. Show all working. AI marks against the real AQA mark scheme.
1 mark Atmosphere composition AQA 8462 P2 style
Approximately what percentage of the modern atmosphere is nitrogen?
A 21%
B 0.04%
C 78%
D 50%
1 mark Oxygen increase AQA 8462 P2 style
What caused oxygen levels in the Earth's atmosphere to increase over billions of years?
A Volcanic activity released oxygen from deep within the Earth
B Water vapour broke down in the upper atmosphere to release oxygen
C Photosynthesis by early algae and plants released oxygen as a by-product
D Rocks gradually released oxygen as they weathered over time
4 marks Greenhouse effect explanation AQA 8462 P2 style
Explain how the greenhouse effect works and why increasing CO₂ levels are causing global warming. (4 marks)
Hint: Short-wave in → Earth warms → emits IR out → greenhouse gases absorb IR → re-emit in all directions → heat trapped. Then link increased CO₂ to enhanced effect.
Mark my answer +40 XP
1 mark Carbon monoxide danger AQA 8462 P2 style
Why is carbon monoxide particularly dangerous as an air pollutant?
A It causes acid rain by reacting with water in clouds
B It has no colour or smell so it cannot be detected without instruments, and it binds to haemoglobin preventing oxygen transport
C It absorbs UV radiation causing stratospheric ozone depletion
D It increases global temperatures as a greenhouse gas
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