All ecosystems have certain common basic features of structure and function. They all have living and non-living components through which there is a flow of energy and exchange of materials. Birth, Growth, death and decay are the four pillars that keep life going on the planet. The soil does not offer an endless supply of minerals to land living organisms nor do fresh water and sea to their inhabitants.
Yet in the millions of years during which life evolved and flourished on land, the soil has not been exhausted of the nutrients required by plants. Similarly, the atmosphere has not run out of its oxygen or carbon dioxide. Shortages of these substances are prevented because they are circulated and recycled in a community in a delicately balanced cycle of events.