Answer: .Early organisms created oxygen from other gases in the atmosphere
Explanation:
It is believed that the atmosphere emerged about 4,500 million years ago, by a process that can be explained in five stages.
In the first stage, the atmosphere was shaped by volcanic emanations, such as water vapor, carbon and sulfur dioxide, and nitrogen. At this point, oxygen was barely present.
In the second stage, as the Earth cooled, the water vapor condensed and formed the oceans. Carbon dioxide reacted with the rocks of the earth's crust to create carbonates - (CO32-); a portion of them, when dissolved in the seas, generated salt water.
In the third stage, approximately 3.500 million years ago, bacteria appear, capable of carrying out photosynthesis, that is, of producing oxygen. This facilitated the development of marine life.
Once the atmosphere obtained sufficient oxygen, the fourth stage appeared, the evolution of large organisms as animals capable of breathing air.
This is how the current atmosphere containing the gases created in each of the previous phases was reached. These are kept in motion by winds and rains, allowing humans, and other living organisms, to breathe. For this reason, without them there would be no life on the planet.
