Geoscience Reference
In-Depth Information
Soils are not everywhere the same. They change remarkably even along small
distances, and when climatic and vegetation conditions change substantially across
large distances, their physical, chemical, and biological properties differ to such an
extent that their similarity is absent, and soils even display huge assortments of dif-
ferent colors across local, regional, and continental landscapes. Variations of soil
are neither chaotic nor by haphazard and correspond to strong relationships imposed
by spatial and temporal environmental conditions according to scientifi c laws. Soils
in tundra regions differ substantially from soils of steppes or prairie lands, and they
again diverge from soils in humid tropics. Even a nonspecialist recognizes differ-
ences according to the color of the soil in a trench or an excavation for a road. A
layman notices that tropical soils are usually not gray or grayish brown but much
more colorful and sometimes refl ect colors of the entire spectrum of a rainbow.
Soils differ substantially not only within great distances of climatic and vegetative
zones but also within much smaller distances. For example, soils vary along the
slope as well as within the valley at the bottom of the slope. Soils are taxonomically
classifi ed into orders, suborders, great groups, subgroups, families, and series in a
similar way as are other natural resources are classifi ed. Taxonomical systems are
not yet globally unifi ed. This is not the only scientifi c disadvantage, but it is a practi-
cal drawback. We have to consider the fact that soils with their crop and animal
productivity are an important basis of the non-predictable daily changing market
values of national economic resources.
Soils are as vulnerable as living organisms. As the environmental system changed
during the geological evolution of our planet and beginning at the time when living
organisms occupied the land, soils developed and changed continually. We can fi nd
sometimes the remnants of those past soils. They are called paleosols and we devote
more attention to them later on in Sect.
13.3
,
Granny Soils. These earlier existing
soils are sometimes buried under the dust and ash of the past volcano eruption, or
they are hidden under thick layers of loess blown by windstorms occurring in the
very cool climate of glacials during the last two million years of Pleistocene. Similar
to a snowdrift, a loessdrift could form to a depth of several meters, but the time for
its development differed greatly from that of snow. Without interruption, loessdrifts
were formed during tens of thousands of years. In this way the paleosol, being older
and lying under the loess, was preserved. In some instances, paleosols are found
hidden below the sediments of rivers.
Abrupt changes of the global environmental system have been caused by the
catastrophic impacts of asteroids or a comet colliding with the Earth. Soils were
completely destroyed - only small remnants have been found under layers of fossil
dust and ash. When such catastrophes happened, soil disappeared from the entire
continents. And after such events, because the climate and vegetation changed, the
new slowly formed soils differed from the earlier soils. Without the impact of an
asteroid, serious soil damage in the last 11,700 years during the Holocene has been
caused by human activity. This damaging activity, strengthened during the previous
two centuries, has recently led to catastrophic consequences in some regions.
In one of civilization's cradles, Mesopotamia, some dynasties collapsed after
introducing a primitive irrigation system that accelerated rather than restricted soil
