The laws of matter state that it can neither be created nor destroyed and earth can be considered a closed system with respect to matter; therefore all matter on earth cycles.
Natural cycles can be defined as the movement (or cycling) of matter or energy through a system. The movement is based on how living things within an Ecosystem interact with each other and also with their non-living environment. These cycles are how the earth renews itself to support life. Sometimes the cycles are gradual and productive while other times the processes can be violent and destructive. Regardless, ecosystems regenerate themselves based on the natural cycling though people can upset these balances in various ways.
Some examples of natural cycles include biogeochemical cycles, plant cycles, energy cycles etc.