How Oxygen Increased

Approximately 2.7 billion years ago, primitive plants and algae began producing oxygen through photosynthesis. During photosynthesis, carbon dioxide and water are converted into glucose and oxygen.

The equation for photosynthesis is:

Carbon dioxide + WaterGlucose + Oxygen

6CO2(g) + 6H2O(l)C6H12O6(aq) + 6O2(g)

As more plants formed, the levels of oxygen in the atmosphere increased. The build-up of oxygen was so significant that it now makes up around 21% of the atmosphere. This increase in oxygen allowed more complex organisms to evolve.

Today, oxygen is essential for the survival of most organisms on Earth. Animals and other organisms depend on it to release energy from food through respiration. Without oxygen, complex organisms could not exist.