Explanation:
This occurred due to the evolution of photosynthetic organisms billions of years ago. Remember photosynthetic organisms take up carbon dioxide and evolve out oxygen as a byproduct in photosynthesis. The proliferation of these organisms caused a change in the atmospheric composition by taking out carbon dioxide and increasing oxygen. This event is known as the Great Oxygenation Event. This also caused a reduction in temperatures in the earth’s atmosphere because of carbon dioxide, which is a greenhouse gas, reduced drastically.
