Nitrogen cycle

On Earth, atoms of the chemical element, nitrogen (atomic symbol, N; number of protons, 7; standard atomic weight, 14.0067 u) &mdash; an essential element for Earth's living systems &mdash; undergo cyclical movement through the atmosphere, the crust (lithosphere), water compartments (hydrosphere), living systems, and non-living organic matter, in a process called the nitrogen cycle, or more specifically, the biogeochemical nitrogen cycle.