Geoscience Reference
In-Depth Information
Chapter 3
Soil Is the Skin of the Planet Earth
We have mentioned earlier in the introductory chapter that recent soil scientists like
to say in their scientifi c jargon that the soil is a sort of skin to our planet Earth. When
we have now more space and the reader has more time, we can afford the luxury of
going into some details. First, this comparison is not exact because we mammals are
born with skin, have it at the beginning of our existence, and continue to have skin
throughout our lives even if it is not in perfect condition upon death. Hearing the
parable about Earth's skin, others may deduce that soil and the Earth were created
simultaneously. Such a conclusion is not valid. The soil, or the Earth's skin as we
used to say, started its existence when macroscopic life was moving from oceans to
the mainland, to the surface of continents and islands. This migration was happen-
ing roughly 500 million years ago - maybe even a little bit earlier. It was the time of
Earth's adolescence and certainly not immediately after the birth of our planet.
During this period, various kinds of proto-soils gradually began to uniquely develop
and slowly appear at diverse locations. Before this time, only weathering fragments
and remnants from rocks - stones, gravels, sands, and even clays - scattered across
continental surfaces, completely void of any action by living macroorganisms.
Without the contributing actions of these organisms, a soil cannot exist. Although
some microorganisms, mainly bacteria, were thriving at that time, their contribution
to the transformation of the weathered inorganic rocky material was negligible and
has not been documented. As our initially skinless planet aged, an outer jacket of
soil eventually became a reality owing to the essential actions of macroscopic life.
Real soil does not exist without such a living community.
Another snag or incongruity can be identifi ed in the everyday analogy that com-
pares the relative thickness of the soil on the Earth to that of the skin of humans or
animals. The soil layer forming the boundary between the Earth and the atmosphere
has a thickness usually of only 1 m, sometimes 2 m, and rarely more than 2 m. This
layer in the context of the Earth's radius of 6,378 km is extremely thin - it is about
six million times smaller than the radius of the Earth. Sometimes the soil layer is
about three million times smaller than the radius of the Earth. Generally, we can say
