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. When single - celled organisms released oxygen into the air through photosynthesis, it gradually built up the oxygen - rich atmosphere that made it possible for more complex life forms to develop and exist on land. Earth's temperature increase causing evaporation doesn't directly relate to life on land in a fundamental way. The collision to form the moon is more related to Earth's formation and early astronomical events rather than life on land. Absorbing harmful gases by single - celled organisms is not as directly related to enabling life on land as oxygen production.

Answer:

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