4.9.1.3 - How oxygen increased

How was the oxygen in our atmosphere first produced?

Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis

Define photosynthesis.

When plants use light to convert carbon dioxide and water into glucose and oxygen.

When did algae first evolve - so when was oxygen first produced?

Algae first produced oxygen about 2.7 billion years ago (when they first evolved) and soon after this oxygen appeared in the atmosphere.

What occurred over the next billion years after the evolution of algae?

Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals (and more complex life)to evolve.

Until eventually about 200 million years ago, the atmosphere reached a composition similar to what it is today