The gaseous oxygen in the Earth's atmosphere was produced as a by-product of
A) volcanic outgassing.
B) photochemical reactions breaking down ozone (O₃) to form oxygen (O₂).
C) photosynthesis.
D) decay of organic matter.

Question

Quizplus · Accepted Answer

Gaseous oxygen in the Earth's atmosphere was produced as a by-product of photosynthesis. This process involves the conversion of carbon dioxide and water into organic compounds and oxygen using sunlight as energy. It is believed that the rise of atmospheric oxygen levels resulted from the emergence of photosynthetic organisms about 2.4 billion years ago.

The Gaseous Oxygen in the Earth's Atmosphere Was Produced as a By-Product