Where does the oxygen in earths atmosphere come from?

Answer 1

The origin of oxygen (and other large elements) is from supernovae.

On the smaller scale, the vast majority of our oxygen comes from ocean plants, from tiny algae to giant kelp. The atmospheric oxygen comes from the decomposition of water and carbon dioxide by organisms that use photosynthesis to make useful molecules in combination with the energy from sun light.

Answer 2

The majority of the oxygen in Earth's atmosphere comes from photosynthesis by plants, algae, and photosynthetic bacteria. These organisms take in carbon dioxide and release oxygen as a byproduct. Additionally, a small amount of oxygen is produced by photolysis in the upper atmosphere, where ultraviolet radiation breaks apart water molecules.

Answer 3

From plants and trees

Answer 4

Plantae (plants)