Geoscience Reference
In-Depth Information
valid for all other processes leading to the creation of soils. Inasmuch as transforma-
tions of various components of organic matter coincide with most of these men-
tioned processes, intermediate and subsequent organic products and by-products
depend upon a complex series of reaction rates. When we compare the complicated
process of creating a soil that takes decades to thousands of years with human or
animal life, we recognize that a soil's existence passes through childhood, adoles-
cence, and adulthood. However, it is more complicated. When external climatic
conditions change, soils may return to their adolescence or even to their childhood
in order to fi nd an alternative path of evolution and aging. And in some instances,
they may even die - akin to the fi nal event of human or animal life. Soil formation
is a very complicated process lasting for a long time and keeping its own dynamics.
The complex system allows substances to enter and leave, while concomitantly
encouraging the acceptance and release of specifi c energies required for critical
soil-forming processes.
Genuine soils fi rst originated about 400-350 million years ago on sediments
along the mouths of rivers fl owing into big lakes and into oceans. These wet porous
media enabled the entrance of primitive plants from the shallow sea onto land. Even
though the sediments were not fi xed owing to the absence of plants and easily
washed and blown away into rivers and oceans, voluminous amounts of weathered
rock materials were available for the birth of soils.
A new situation began when the fi rst pioneering plants found their feet in soils.
With their roots actively aggregating the originally loose sand, silt, and clay materi-
als, plants protected the sediments and developing aggregates from the continuous,
relentless splash of water that previously washed them down into rivers, lakes, and
oceans. The plants also reduced the blowing force of strong winds and tornadoes.
When the plants died, their dead remains provided perfect nourishment for the
microorganisms already present that were busy taking the energy released as they
disturbed the chemical bonds in rocks and minerals. Other troops of microorgan-
isms were moving from waters of oceans and rivers ashore into the pores of sedi-
ments, driven by the chance of fi nding residues of plants and nutritional ingredients
in excess. However, because not all pores were fi lled completely with water, they
had to accustom themselves to their new environment. As a result, new families of
microorganisms evolved as they adapted to the fl ip-fl op tactics of water and air -
that is, the solid surfaces of pores on which they resided were sometimes completely
surrounded with free liquid water, and at other times, the microorganisms were
touched by varying amounts of air that partially fi lled the pores. This variation of
both air and water was the situation when nearly sterile mineral sediments started to
attract colonies of microorganisms and subsequently attracted emerging plants.
Such sediments serving as a home for microorganisms that modifi ed local physical
and chemical properties also became a home for plants. The higher the density of
microorganisms, the more attractive was the newly formed home for plants. This
home was the birth of new global environment we now call soil. Soils fi rst origi-
nated near the water of rivers and seas. Then in the run of million years, the soil-
forming processes were extending together with pioneer plants into regions more
distant from rivers and oceans. Ultimately, soil occupied all terrestrial regions of
