The large amount of free oxygen in Earth's present atmosphere is primarily a result of
A) outgassing by volcanoes and other geological processes.
B) biological processes such as photosynthesis.
C) splitting of carbon dioxide into carbon and oxygen by solar ultraviolet light.
D) carbon dioxide becoming dissolved in the oceans, releasing oxygen.

Question

Quizplus · Accepted Answer

The large amount of free oxygen in Earth's atmosphere is primarily due to photosynthesis, a biological process where plants, algae, and certain bacteria convert carbon dioxide and water into glucose and oxygen using sunlight.

The Large Amount of Free Oxygen in Earth's Present Atmosphere