Geoscience Reference
In-Depth Information
before the Middle Ages - that is, burning wood, watering the product of burning,
and next evaporating the solution in a pot. The Neo-Latin kalium has its roots in the
word alkali which was derived from the Arabic
al-qalyah
that also means plant
ashes. The stable, mainly occurring
39
K is related to the non-stable isotope
40
K with
a half-life of 1.25 billion years that decays to stable argon
40
Ar. The ratio of these
two K isotopes applied for a very long time between 100,000 and 4 billion years BP
is generally used for estimating the age of biotite and volcanic rocks. The use of
uranium isotopes does not strictly fi t the method derived for carbon dating because
all three natural isotopes of uranium are unstable and decay differently. Although
several alternate procedures have been developed for uranium age dating, the appli-
cation of
238
U/
206
Pb with a half-life 4.5 billion years is decisive and is applicable for
ascertaining ages for times less than the half-life. Reliable dating was successfully
achieved. Rubidium and strontium isotopes
87
Rb/
87
Sr provide age dating opportuni-
ties, too, similar to isotopes
85
Kr and
3
H/
3
He.
With paleosols never being found as undisturbed soil profi les, researchers gener-
ally discover only small parts of the original profi le, or on rare occasions when they
have good luck, they fi nd intact segments of the original horizons. Usually they have
to study micromorphological bodies in the complete absence of macroaggregates.
The main task is to describe the shape of microaggregates and the material of globu-
lar components similar to microspheres. Additionally, the shape and material of thin
fi lms covering silt and sand particles, the cutans, are described. The name for these
microforms, introduced in 1964 by Roy Brewer, was accepted by soil scientists.
Based on fabric and shape of cutans, local conditions of soil evolution are classifi ed.
The main grouping of cutan fabric into major categories is as follows: carbonates,
iron oxides (sesquans), organic matter (organans), and type of clay minerals (argil-
lans). The kind of solid surface of silt and sand also plays an important role in the
formation of the shape of cutans. In addition to particle cutans, there are ped cutans
covering the surface of microporous peds and void cutans fi lling the micro-voids
where the particles contact each other. With cutans being further subdivided into
products of eluviation, illuviation, diffusion, and stress action, details of soil pro-
cesses can be identifi ed. Through them, the soil type is detected as it was evolved in
the past. Occasionally, other remnants of weathering could also be found.
For example, if kaolinites prevail in clays of cutans of the soil protected now
from recent climate change and vegetation, soil paleontologists will search for iron
concretions. And if they fi nd them, they will tentatively accept the hypothesis of
Latosol evolution during the past era and will try to confi rm their assumption by
other evidence. Finding paleopedologic evidence that the climate was warmer and
more humid in that specifi c era, they verify and accept their hypothesis of Latosol
evolution. When there are residues of Vertisol evolution characterized by traces of
distinct swelling in rainy seasons and shrinkage during rainless seasons, the paleo-
soil scientist will study the thin fi lms on micro-cracks within soil microsections.
The cutan coating of microaggregates is similarly studied. Because this type of
research requires observations at the microscopic or even nanoscopic level, studies
were performed only recently using contemporary fi ne instrumentation that enabled
chemical and shape analysis to be realized on ultramicroscopic size of soil samples.
