Tracey Robinson, age 12, of North Vancouver, B.C., Canada, for her question:
WHAT CAUSES SUBSTANCES TO DECAY?
Most of us tend to shun decaying substances. As usual, this attitude is about halfway sensible. For example, there is no reason to shudder and feel stricken with horror. But decaying substances usually harbor germs and other pests and it is wise to refrain from handling such stuff as rotting garbage with bare hands.
Nature is an excellent housekeeper on a global scale. Living things create countless tons of waste materials every day. However, nothing is discarded, and numerous operations work to recycle all materials back into useful production. The most important of these garbage disposal projects is the process of decay.
Animals produce waste materials and eventually depart, leaving their dead bodies. Trees shed their leaves, and finally their woody trunks become too weak to stand. Every day the world of nature is littered with a large assortment of waste materials. Every day all sorts of decaying processes break apart these used substances to be reused and recycled throughout the land of the living.
Usually the decaying process is started by larger creatures and finished by mini organisms, too small to be seen. The bodies of sizable animals may be partly consumed by vultures and other carrion eaters. The crumbs may be consumed by various beetles, mites and an assortment of other soil dwelling insects. Earthworms feast on fallen leaves.
These visible projects remove sizable chunks of garbage from the landscape. But tons of crumbly waste are left behind. This material provides food for a multitude of microscopic plants and animals. Some are molds and mildews. Most of them are decay bacteria of various types. As nutrients are absorbed, molecules built by living plants and animals are broken apart into simpler substances.
Normal soil teems with assorted decay bacteria that break up plant cells. Some of the simpler materials are reused by living plants to build more of their hydrocarbons. Soil also contains decay bacteria that release smelly gases as they break up animal wastes. Some of these bacteria are unfriendly germs but eventually the messy decaying material is converted to dusty dirt.