When animals and plants die, they decompose
surprisingly quickly. The body of an adult
human, if exposed to the elements, is reduced
to a mere skeleton in about three weeks.
The bones last longer, but not a great deal.
Shakespeare was right when his gravedigger
in Hamlet (Act V, Scene I) estimated there
was not much left of a cadaver after eight or
nine years. Even huge trees go the same way,
and about as quickly.
The end product of this composting process is a remarkably
resistant and complex organic substance called humus, which
is largely responsible for the brown color of the majority of
soils in temperate regions.
Humus is a mixture of the highly altered remains of the
original organic matter—whether from plants or animals—that
arrives at the soil surface, as well as new compounds made by
bacteria and fungi. But only a small fraction of the original
material is destined to become humus. Most simply disappears,
turned back into the carbon dioxide (CO2), water, and mineral
salts from which it was first made.
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