Answer:
The Great Oxygenation Event
Step-by-step explanation:
The Great Oxygenation Event was the moment that the Earth's atmosphere began to establish a large amount of oxygen, which allowed life on the planet more directly.
Before this event, the earth was already inhabited by unicellular and anaerobic beings, however, as you may already know, oxygen is fundamental for the survival of most living beings, which did not exist before this element was established in large quantities in our atmosphere. .
This event happened when some of these single-celled beings (especially ancestors of cyanobacteria) began to make photosynthesis. One of the final products of photosynthesis is the release of oxygen into the atmosphere and it was in this way that the planet earth was able to shelter more complex life forms.