Today,the pathways of photosynthesis and cellular respiration are complementary and relatively balanced,but early in the history of life on Earth,photosynthesis appears to have dominated.One piece of evidence that suggests the early dominance of photosynthesis is the
A) accumulation of atmospheric oxygen.
B) declines in historic sea levels as photosynthetic organisms consumed water.
C) gradual warming of Earth's climate as CO₂ slowly accumulated.
D) sequestration of O₂ in Earth's oceans.

Question

Quizplus · Accepted Answer

The accumulation of atmospheric oxygen is a clear indication of the dominance of photosynthesis in the early history of life on Earth, as oxygen is a byproduct of photosynthesis. The increase in atmospheric oxygen levels occurred over a long period of time as photosynthetic organisms continuously produced oxygen through the process of photosynthesis. The oxygen eventually oxidized and eliminated most of the reducing agents present in the early Earth's environment. This led to the evolution of cellular respiration as a way for organisms to extract energy from organic molecules using oxygen in the environment as an electron acceptor.

Today,the Pathways of Photosynthesis and Cellular Respiration Are Complementary and Relatively