Why on earth do not end the same substances from which living organisms have been building

Why on earth do not end the same substances from which living organisms have been building for millions of years and continue to build their bodies?

The Earth is a closed system of circulation of chemical elements. There is a law of conservation of matter, according to which nothing is taken from anywhere and disappears into nowhere. If a person accumulates various chemical substances in the body during his life, after his death, not a single element will disappear anywhere. Also, the number of elements remains unchanged. Thus, chemical elements circulate in nature, feeding first one creature, and after his death, the next creature.