The Earth's atmosphere is the gaseous layer surrounding our planet...
Chemistry232 views·Updated 20 Jun 2026·4 pagesGCSE Chemistry Notes: Atmosphere - Topic 9 AQA Overview
1 / 4
1
of 4
The Atmosphere's Composition
Our atmosphere today consists mostly of nitrogen (78%) and oxygen (21%), with small amounts of other gases including carbon dioxide, water vapour and noble gases. This composition has remained relatively stable for about 200 million years, but it wasn't always this way.
During Earth's first billion years, intense volcanic activity released gases that formed the early atmosphere, primarily water vapour and carbon dioxide. As the planet cooled, water vapour condensed to form oceans, but carbon dioxide remained dominant in the atmosphere—similar to what we see today on Mars and Venus.
Carbon dioxide levels decreased over time through several natural processes. The gas dissolved in oceans, creating a weak acid that reacted with minerals to form precipitates. These eventually became sediments of carbonate rock on the sea bed. Marine organisms like corals and mussels also used carbon dioxide to create their shells, which later formed limestone when they died.
Did you know? The limestone formations we see today represent carbon dioxide that was once in the atmosphere, showing how Earth naturally sequestered carbon over millions of years!
2
of 4
The Rise of Oxygen and Fossil Fuels
About 1.7 billion years ago, a major atmospheric shift began when photosynthetic algae evolved in the oceans. These simple organisms produced oxygen as a byproduct of photosynthesis. As plants later evolved on land, oxygen levels continued to increase until they reached a point where animal life could develop.
While oxygen levels rose, carbon dioxide was being trapped in what we now call fossil fuels. Coal formed when plant material in marshy wetlands didn't fully decompose due to lack of oxygen or acidic conditions. Under high pressure and temperature over millions of years, this plant matter transformed into coal.
Crude oil and natural gas formed similarly but from marine organisms. When plankton died and settled in mud on the sea floor, their remains were preserved without decomposition if oxygen was absent. Gradually, heat and pressure transformed these remains—plankton became crude oil, while natural gas (primarily methane) often formed nearby.
Important: The greenhouse effect is actually natural and necessary! Without it, Earth would be too cold for life. Gases like carbon dioxide, water vapour and methane trap the sun's heat by allowing short-wavelength radiation in but absorbing the long-wavelength radiation that the Earth radiates back.
3
of 4
Climate Change and Solutions
Human activities have significantly altered atmospheric composition, particularly through deforestation and fossil fuel use. Cutting down forests not only removes carbon-absorbing trees but also releases stored CO₂. Meanwhile, agriculture—especially cattle farming—produces large amounts of methane, another powerful greenhouse gas.
The impacts of these changes are already visible: melting polar ice, rising sea levels, more severe weather patterns, and shifting distributions of plants, animals and diseases like malaria. While climate models are complex and sometimes lead to simplified predictions, the evidence for human-caused climate change is overwhelming.
Reducing our carbon footprint—the total amount of greenhouse gases produced through our activities—requires both individual and societal changes. Simple steps include better home insulation, using public transport instead of cars, switching to renewable energy sources, and reducing electricity consumption. Eating less beef and dairy also helps reduce methane emissions.
Take action: Calculate your personal carbon footprint online to see which of your daily activities contribute most to greenhouse gas emissions. You might be surprised by what makes the biggest impact!
4
of 4
Air Pollution from Fuels
When we burn fossil fuels like coal and hydrocarbons, they release several harmful pollutants. The carbon and hydrogen in these fuels react with oxygen in the air to produce various compounds, some quite dangerous to human health.
Carbon monoxide is a toxic gas produced by incomplete combustion. It has no colour or smell, making it particularly dangerous—which is why carbon monoxide detectors in homes are so important. When coal containing sulfur is burned, it produces sulfur dioxide, which causes breathing problems and contributes to acid rain.
Vehicles create another set of pollutants. The high temperatures in car engines cause nitrogen and oxygen in the air to react, forming various nitrogen oxides (NOx). These, along with sulfur dioxide, dissolve in rainwater to create acid rain that damages trees and buildings. Cars also release particulates—tiny unburned hydrocarbon particles that increase the risk of heart and lung disease.
Health alert: Air pollution isn't just an environmental issue—it's a major health concern. The World Health Organization estimates that air pollution contributes to millions of premature deaths annually, primarily from respiratory and cardiovascular diseases.
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Chemistry232 views·Updated 20 Jun 2026·4 pagesGCSE Chemistry Notes: Atmosphere - Topic 9 AQA Overview
The Earth's atmosphere is the gaseous layer surrounding our planet that enables all life. Its composition has changed dramatically over billions of years, from a carbon dioxide-rich environment to the nitrogen-oxygen rich air we breathe today. Understanding these changes helps...
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The Atmosphere's Composition
Our atmosphere today consists mostly of nitrogen (78%) and oxygen (21%), with small amounts of other gases including carbon dioxide, water vapour and noble gases. This composition has remained relatively stable for about 200 million years, but it wasn't always this way.
During Earth's first billion years, intense volcanic activity released gases that formed the early atmosphere, primarily water vapour and carbon dioxide. As the planet cooled, water vapour condensed to form oceans, but carbon dioxide remained dominant in the atmosphere—similar to what we see today on Mars and Venus.
Carbon dioxide levels decreased over time through several natural processes. The gas dissolved in oceans, creating a weak acid that reacted with minerals to form precipitates. These eventually became sediments of carbonate rock on the sea bed. Marine organisms like corals and mussels also used carbon dioxide to create their shells, which later formed limestone when they died.
Did you know? The limestone formations we see today represent carbon dioxide that was once in the atmosphere, showing how Earth naturally sequestered carbon over millions of years!
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The Rise of Oxygen and Fossil Fuels
About 1.7 billion years ago, a major atmospheric shift began when photosynthetic algae evolved in the oceans. These simple organisms produced oxygen as a byproduct of photosynthesis. As plants later evolved on land, oxygen levels continued to increase until they reached a point where animal life could develop.
While oxygen levels rose, carbon dioxide was being trapped in what we now call fossil fuels. Coal formed when plant material in marshy wetlands didn't fully decompose due to lack of oxygen or acidic conditions. Under high pressure and temperature over millions of years, this plant matter transformed into coal.
Crude oil and natural gas formed similarly but from marine organisms. When plankton died and settled in mud on the sea floor, their remains were preserved without decomposition if oxygen was absent. Gradually, heat and pressure transformed these remains—plankton became crude oil, while natural gas (primarily methane) often formed nearby.
Important: The greenhouse effect is actually natural and necessary! Without it, Earth would be too cold for life. Gases like carbon dioxide, water vapour and methane trap the sun's heat by allowing short-wavelength radiation in but absorbing the long-wavelength radiation that the Earth radiates back.
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The impacts of these changes are already visible: melting polar ice, rising sea levels, more severe weather patterns, and shifting distributions of plants, animals and diseases like malaria. While climate models are complex and sometimes lead to simplified predictions, the evidence for human-caused climate change is overwhelming.
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