Explain oxygen cycle in brief.
The oxygen cycle is the?biogeochemical cycle ?of? oxygen? within its four main reservoirs: the?atmosphere?(air), the total content of biological matter within the?biosphere?(the global sum of all ecosystems), the?hydrosphere?(the combined mass of water found on, under, and over the surface of planet Earth), and the?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 in its current form (see the?Great Oxygenation Event).