Most natural solid waste is recycled by the process of decay. Think about it, air and water don't rot. The only things that are recycled by rotting/or falling apart are solid things.
In biology, the process of decay (decomposition) describes the metabolic degradation of organic matter into simple organic compounds such as nitrogen, for example, and inorganic with energy release. It is often equated with rot, which is different because it results from mold and not from the activity of decomposers.
The science that studies decomposition is generally referred to as taphonomy.
