Chemical cycling describes systems of repeated circulation of chemicals between other compounds, states and materials, and back to their original state, that occurs in space, and on many objects in space including the Earth. Active chemical cycling is known to occur in stars, many planets and natural satellites.
Chemical cycling plays a large role in sustaining planetary atmospheres, liquids and biological processes and can greatly influence weather and climate. Some chemical cycles release renewable energy, others may give rise to complex chemical reactions, organic compounds and prebiotic chemistry. On terrestrial bodies such as the Earth, chemical cycles involving the lithosphere are known as geochemical cycles. Ongoing geochemical cycles are one of the main attributes of geologically active worlds. A chemical cycle involving a biosphere is known as a biogeochemical cycle.