It is the second most abundant element in the earth’s atmosphere by volume after nitrogen. Oxygen forms about 21 percent of the atmospheric gases. It is an essential element for the building up of living organisms and its life processes such as respiration.
The Oxygen Reservoirs Are:
- Atmosphere –In terms of volume, 21 percent of Oxygen is present as free oxygen molecules, ozone, carbon dioxide, sulfur, water vapor, and nitrogen oxides.
- Biosphere – Oxygen is present at about 22 percent by volume as a compound of organic molecules and water molecules.