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:

Oxygen is crucial for most land - based life forms for respiration. Single - celled organisms performing photosynthesis released oxygen into the atmosphere, which gradually made the Earth's atmosphere suitable for the evolution and existence of land life. Earth's temperature increase causing evaporation doesn't directly relate to oxygen availability for land life. The collision to form the moon has no direct connection to land life existence. Absorbing harmful gases by single - celled organisms is not as directly related to enabling land life as oxygen production.

Answer:

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