In
Earth science, a
biogeochemical cycle or
substance turnover or
cycling of substances is a pathway by which a
chemical substance moves through both biotic (
biosphere) and abiotic (
lithosphere,
atmosphere, and
hydrosphere) compartments of
Earth. A cycle is a series of change which comes back to the starting point and which can be repeated. Water, for example, is always recycled through the
water cycle, as shown in the diagram. The water undergoes
evaporation,
condensation, and
precipitation, falling back to Earth. Elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another through biogeochemical cycles.'