The living microbial biomass includes<span> the microorganisms responsible for decomposition (breakdown) of both plant residues and active </span>soil organic matter<span> or detritus. Humus is the stable fraction of the </span>soil organic matter<span> that is formed from decomposed plant and animal tissue. It is the final product of decomposition.</span>
The Earth's rocky outer crust solidified billions of
years ago, soon after the Earth formed. This crust is not a solid
shell; it is broken up into huge, thick plates that drift atop the soft,
underlying mantle.
The plates are made of rock and drift all over the globe; they move both
horizontally (sideways) and vertically (up and down). Over long
periods of time, the plates also change in size as their margins are
added to, crushed together, or pushed back into the Earth's mantle. These plates are from 50 to 250 miles (80 to 400 km) thick.
Industrial development resulting in pollution.