Geoscience Reference
In-Depth Information
Chapter 5
The Birth of Soils
Readers, at this moment, we beg each of you not to get discouraged as you wade
through this chapter, the longest one in our topic, trying to grasp all of the essential
facets of the birth of any soil. To explain and interconnect each of them required
elucidation of a network of physical, chemical, and biological processes occurring
together within specifi c domains below and above the Earth's surface during various
time intervals ranging between microseconds and thousands of years. Sit tight while
you read and perhaps reread parts of it before we proceed together into the next
chapter.
Soils are never born all of a sudden like a woman delivers a baby or cow delivers
a calf, nor is the origin of a soil a relatively rapid process like the germination of a
plant from a moist seed. At this point, our inclination to compare soils with living
organisms is limping along in an unconvincing manner. Actually, the birth of a soil
begins with gradual transformations of its originating materials, usually compact
rocks or their weathering products that vary in size from big stones to dust particles.
During the time of fl oods, the smaller particles are transported by water mainly to a
neighborhood of rivers or by rivers into an ocean where they settle down to initially
form a muddy riverbed or seabed. After the fl ood, the muddy material gradually
becomes dried out, compacted, and chemically fi xed to eventually form a solid,
sedimentary rock - after which, the process of weathering starts all over again.
Sometimes the particles are transported by wind during dust storms. The trans-
ported material could be enriched by decayed plant residuals that glue the small
mineral dust particles together. Much less frequently, whenever excessive amounts
of plant residues prevail in stagnant water enriched with small mineral particles,
another member of the family of soils, peat, makes its appearance.
Combinations of many individual reactions running at the same time and infl u-
encing each other create the initial transformation of the dense mineral matter.
Moreover, the rates of reactions increase or decrease with time. Since they are trig-
gered by outside factors and since those factors are frequently not constant in time,
the weathering rates of rocks during any given time period may be consistently high
or low as well as remarkably stable or variable during other periods. The same is
