The primary source of oxygen for the earth's atmosphere during the past half billion years or so appears to be
A) volcanic eruptions.
B) photosynthesis.
C) photodissociation.
D) exhalations of animal life.
E) transpiration.

Question

Quizplus · Accepted Answer

Photosynthesis by plants and other photosynthetic organisms, such as algae and some bacteria, has been the primary source of oxygen for the earth's atmosphere for the past half billion years. Through the process of photosynthesis, these organisms convert carbon dioxide and water into organic molecules and oxygen, which is released into the atmosphere.

The Primary Source of Oxygen for the Earth's Atmosphere During