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The composition and evolution of the Earth's atmosphere
This topic links the gases in today's atmosphere with theories about volcanic activity, oceans, photosynthesis and the removal of carbon dioxide.
27
Objectives
135
Flashcards
135
Questions
90 min
Study time
AQAGCSEChemistryChemistry of the atmosphere
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Syllabus checklist
What you need to know
27 objective pages available
The proportions of different gases in the atmosphere6 objectives
- Recall that the Earth's atmosphere is about 80 percent nitrogen.
- Recall that the Earth's atmosphere is about 20 percent oxygen.
- Recall that the Earth's atmosphere contains small proportions of other gases including carbon dioxide, water vapour and noble gases.
- Interpret simple data showing the proportions of gases in the atmosphere.
- Distinguish the major gases in the present atmosphere from trace atmospheric gases.
- Explain why percentage composition is useful when describing atmospheric gases.
The Earth's early atmosphere8 objectives
- Describe the Earth's early atmosphere as probably containing mainly carbon dioxide with little or no oxygen.
- Explain that volcanic activity released gases that formed the early atmosphere.
- Recall that volcanoes released carbon dioxide, water vapour and nitrogen.
- Explain that water vapour condensed to form the oceans as the Earth cooled.
- Describe possible early atmospheric gases including methane and ammonia.
- Compare the early atmosphere with the present atmosphere.
- Explain why there are several theories about the Earth's early atmosphere.
- Evaluate evidence and uncertainty when discussing the Earth's early atmosphere.
How oxygen increased5 objectives
- Explain that algae and plants produced oxygen by photosynthesis.
- Explain that photosynthesis removed carbon dioxide from the atmosphere.
- Describe how oxygen levels increased gradually as photosynthetic organisms became more widespread.
- Link the increase in atmospheric oxygen to the development of more complex life.
- Interpret simple evidence for changes in atmospheric oxygen over time.
How carbon dioxide decreased8 objectives
- Explain that carbon dioxide dissolved in the oceans as the atmosphere changed.
- Explain that dissolved carbon dioxide was used to form carbonate precipitates.
- Describe how carbonate precipitates formed sediments that became sedimentary rocks.
- Explain that marine organisms used carbonates to make shells and skeletons.
- Explain that some carbon was trapped in fossil fuels formed from dead organisms.
- Describe limestone, coal, crude oil and natural gas as long-term carbon stores.
- Explain why the amount of carbon dioxide in the atmosphere decreased over geological time.
- Link carbon dioxide removal to changes in the carbon cycle.
Key terms
nitrogenatmosphereEarth's atmosphereoxygencarbon dioxidewater vapourproportionsmajor gasestrace gasespercentage compositionatmospheric gasesearly atmosphere
Exam tips
- Remember Nitrogen Proportion: Remember to memorize that the Earth's atmosphere is approximately 80% nitrogen to quickly recall this key fact during the exam. Link your answer to The proportions of different gases in the atmosphere in The composition and evolution of the Earth's atmosphere, and keep the biology specific to atmosphere.
- Remember Oxygen's Proportion: Remember to memorize that oxygen makes up about 20 percent of the Earth's atmosphere. Link your answer to The proportions of different gases in the atmosphere in The composition and evolution of the Earth's atmosphere, and keep the biology specific to atmosphere.
Common mistakes
- Nitrogen Proportion Confusion: To fix this, students should remember that nitrogen makes up the majority of the atmosphere at about 80 percent, while oxygen is around 20 percent.
- Oxygen Proportion Misunderstanding: Remember that the Earth's atmosphere is about 20 percent oxygen and 80 percent nitrogen. Use mnemonic devices or visual aids to help memorize these proportions.
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