Question

Which event in Earth’s history most directly allowed life to exist on land?

Earth’s 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.

Answer 1

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

Explanation: Oxygen from photosynthetic microbes (cyanobacteria) built up in the atmosphere, allowing an ozone layer to form (blocking harmful UV) and enabling aerobic respiration, both of which made complex life and colonization of land possible.