The $\underline{\text{primary}}$ source of oxygen for Earth's atmosphere during the past half billion years or so appears to be
A)volcanic eruptions.
B)photosynthesis.
C)radiant heat.
D)exhalations of animal life.
E)transpiration.

Question

The $\underline{\text{primary}}$ source of oxygen for Earth's atmosphere during the past half billion years or so appears to be
A)volcanic eruptions.
B)photosynthesis.
C)​radiant heat.
D)​exhalations of animal life.
E)​transpiration.

Quizplus · Accepted Answer

Photosynthesis is the process by which plants and some bacteria use sunlight to synthesize foods with the help of chlorophyll, producing oxygen as a byproduct. This process has been the primary source of atmospheric oxygen for the past half billion years or so. Other options such as volcanic eruptions and animal respiration may contribute to the oxygen levels in the atmosphere, but they are not the primary source.

The primary‾\underline{\text{primary}}primary​ Source of Oxygen for Earth's Atmosphere During the Past Half

The $\underline{\text{primary}}$ Source of Oxygen for Earth's Atmosphere During the Past Half