The Earth formed 4.5 billion years ago as a molten ball, and its early atmosphere consisted of gases like carbon dioxide and water vapor released by volcanoes. As the planet cooled, oceans formed from condensed water vapor. Algae evolved around 3.4 billion years ago and began producing oxygen through photosynthesis, causing oxygen levels in the atmosphere to steadily rise over billions of years. Modern animals later evolved to use oxygen for respiration.

1. Earth’s Atmosphere

2. 4.5 billion years ago
• The Earth was a molten ball of rock and minerals.

3. 4.5-3.5 billion years ago
• The Earth’s surface was covered in
volcanoes releasing carbon dioxide, water
vapour and nitrogen

4. • The water vapour condensed as the Earth
cooled and rain fell. This formed the first
oceans.

5. • Comets also brought water adding to what
we had.

6. • Earth’s early atmosphere consists of carbon
dioxide, with some water vapour, nitrogen
and traces of methane and ammonia.

7. Life began 3.4 billion years ago
• Bacteria first appeared

8. Algae and other life forms evolved
• They could make their own food using the
sun’s energy and oxygen was their waste.

9. 2 billion years ago
• Oxygen levels rose steadily as algae and
bacteria filled the seas.

10. Animals evolved
A comb jelly
• Using oxygen to respire

11. Our atmosphere today