GCSE Chemistry revision

The proportions of different gases in the atmosphere

The composition and evolution of the Earth's atmosphere

AQA 4.9.1.1 Foundation & Higher

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The Earth's atmosphere today is made up of approximately 80% nitrogen, 20% oxygen, and less than 1% of other gases including carbon dioxide, water vapour, and the noble gases.

When algae and plants died, they sank to the seabed and became buried under layers of sediment, trapping carbon and preventing it from returning to the atmosphere.
Over millions of years, compressed sediment formed sedimentary rocks, crude oil, and natural gas, collectively known as fossil fuels.
Crude oil and natural gas formed mainly from dead plankton, which are tiny organisms that float in the ocean.

2. Carbon Storage in Sediments and Fossil Fuels AQA

When algae and plants died, they sank to the seabed and became buried under layers of sediment, trapping carbon and preventing it from returning to the atmosphere.
Over millions of years, compressed sediment formed sedimentary rocks, crude oil, and natural gas, collectively known as fossil fuels.
Crude oil and natural gas formed mainly from dead plankton, which are tiny organisms that float in the ocean.

Coal is a sedimentary rock formed from thick deposits of compressed dead plant material over millions of years.
Limestone is a sedimentary rock composed mainly of calcium carbonate, derived from the shells and skeletons of marine organisms.

Stage 1: Intense volcanic activity produced a carbon dioxide-rich atmosphere with water vapour and nitrogen during the first billion years.
Stage 2: Water vapour condensed to form the oceans, which dissolved much of the atmospheric carbon dioxide.
Stage 3: Photosynthesis by algae and green plants steadily decreased carbon dioxide levels and increased oxygen levels, leading to the nitrogen- and oxygen-rich atmosphere we have today.

4. Summary / Key Terms AQA

Stage 1: Intense volcanic activity produced a carbon dioxide-rich atmosphere with water vapour and nitrogen during the first billion years.
Stage 2: Water vapour condensed to form the oceans, which dissolved much of the atmospheric carbon dioxide.
Stage 3: Photosynthesis by algae and green plants steadily decreased carbon dioxide levels and increased oxygen levels, leading to the nitrogen- and oxygen-rich atmosphere we have today.