Why is there free oxygen in the air?
A)Organisms need oxygen to manufacture ATP.
B)Free oxygen has been present since the formation of the earth's atmosphere.
C)Evaporation of the oceans liberated oxygen.
D)It is a by-product of photosynthesis.
E)Free oxygen has seeped from cracks in the earth's crust.

Question

Quizplus · Accepted Answer

Free oxygen in the air is a by-product of photosynthesis, which is carried out by plants and other organisms. During photosynthesis, plants use energy from the sun to convert carbon dioxide and water into glucose and oxygen. The oxygen is then released into the atmosphere as a waste product. This process has been occurring on Earth for billions of years and has gradually increased the concentration of oxygen in the atmosphere.

Why Is There Free Oxygen in the Air