What does oxygen cycle mean?

The oxygen cycle is the biogeochemical cycle of oxygen in its four main reservoirs: the atmosphere (air), the total content of biological matter in the biosphere (the global sum of all ecosystems), the hydrosphere (a combination of water masses found on, below, and above the surface of planet Earth), and lithosphere / earth's crust. The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life on Earth (see the Great Oxygenation Event).

The oxygen cycle is the cycle that helps move oxygen through the three main regions of the Earth, the Atmosphere, Biosphere, and Lithosphere. The atmosphere, of course, is a region of gas that is located above the earth's surface and is one of the largest free oxygen reservoirs on earth. Biosphere is the sum of all Earth ecosystems. It also has some free oxygen produced from photosynthesis and other life processes. The largest oxygen reservoir is the lithosphere. Most of this oxygen is not alone or moves freely but is part of chemical compounds such as silicates and oxides.