Matter must cycle continuously in order for organisms to continue to exist.
Except for the particles making up the solar wind, the earth has a finite amount of matter from which to make rocks, soils, rivers, plants, animals and other life forms. The total amount of matter present today is close to the total amount of matter that existed when Earth reached its current state. When organisms die, bacteria, fungi, and protists digest them and return the matter they contained to the environment. If matter didn't cycle through the environment, the amount of matter would reduce until there could be no life on earth.