Question

which event in earths history most directly allowed life to exist on land? earths temperatures increased, causing widespread evaporation. earth collided with a large object, forming the moon. single - celled organisms released oxygen into the air when they photosynthesized. single - celled organisms absorbed harmful gases from the air when they first formed.

Explanation:

Single - celled organisms performing photosynthesis released oxygen into the air. Oxygen is crucial for the development and sustenance of aerobic life forms on land. The other events like the Earth - moon formation collision and temperature - related evaporation are not directly related to the existence of life on land in the way oxygen release is. Absorbing harmful gases is not the key factor for life to exist on land compared to oxygen release.

Answer:

Single - celled organisms released oxygen into the air when they photosynthesized.