Scientists infer that oxygen first began to enter the Earth's atmosphere after the appearance of the great oxidation event.
The great oxidation event was a time in history that earth's atmosphere was said to have experienced a great deal of oxygen.
During this period there was a rise in the amount of oxygen on the seas and also on the atmosphere.
Read more about the great oxidation event here:
https://brainly.com/question/20908125?referrer=searchResults
