The Earth's Atmosphere

The Earth’s atmosphere hasn’t always been the way it is today. Billions of years ago, it looked very different. In this topic, you’ll explore how the atmosphere formed, what it's made of today, and how human activity is changing it — along with the consequences for the planet and our health.

The Evolution of the Atmosphere

The Earth’s early atmosphere was formed by volcanic activity. These volcanoes released huge amounts of gases, including carbon dioxide, water vapour, methane, and ammonia — but there was very little oxygen.

As the planet cooled, water vapour condensed to form oceans. Some gases dissolved into the oceans, while early photosynthesising plants (like algae) began to absorb carbon dioxide and release oxygen. Over time, oxygen levels rose and carbon dioxide levels fell, leading to the composition of the atmosphere we have today.

Today’s Atmosphere

The modern atmosphere is mostly:

• 78% nitrogen
• 21% oxygen
• Small amounts of carbon dioxide, water vapour, and noble gases

Greenhouse Gases and Climate Change

Greenhouse gases (mainly carbon dioxide, methane, and water vapour) trap heat from the Sun, keeping the Earth warm. This is called the greenhouse effect — and it’s natural and necessary for life.

But human activities — like burning fossil fuels, deforestation, and agriculture — are increasing greenhouse gas levels, leading to global warming and climate change.

Consequences of Climate Change

Some key consequences include:

• Rising sea levels from melting ice caps
• More extreme weather (floods, droughts, hurricanes)
• Changes to wildlife habitats and food chains
• Reduced biodiversity

Carbon Footprint & Reducing Emissions

A carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted directly or indirectly by an individual, product, or organisation.

We can reduce our carbon footprint by:

• Using renewable energy
• Reducing car use or flying less
• Eating less meat
• Improving energy efficiency in homes and businesses

However, reducing emissions can be difficult due to:

• Economic costs
• Political disagreements
• Lifestyle resistance from individuals and industries

Air Pollution and Fossil Fuels

Burning fossil fuels doesn’t just release greenhouse gases — it also produces air pollutants, such as:

• Sulfur dioxide, which causes acid rain
• Particulates, which contribute to smog and health problems
• Nitrogen oxides, which can damage lungs and plants

Understanding these pollutants helps us improve air quality and make better environmental decisions.

Also see Using Earth's Resources, Crude Oil & Fuels, Chemical Changes

Links for Learning

Bitesize: Developing the atmosphere
Bitesize: Polluting the atmosphere
Revision World: Changes to the Earth and Atmosphere
Revision World: Changes to the Earth and Atmosphere