Geoscience Reference
In-Depth Information
between the features of discovered paleosols and the impacts of climate, surface
morphology, and plants responsible for their formation and evolution. Because he
considered paleosols as reliable sources of information about climate and universal
soil-forming factors at the time of their origin, Glinka was ahead of his contempo-
raries by more than a quarter of the century. His ability to understand broad, univer-
sal links encouraged and enhanced cooperation with soil scientists abroad and
accounts for him being one of the cofounders of the International Soil Science
Society in Rome in 1924.
One relationship that has proven useful for paleosols is that between the depth to
the calcic horizon and the mean annual rainfall. A new compilation of data pre-
sented here demonstrates that this relationship holds throughout the world for arid
land soils. The use of this relationship for interpreting the paleoclimate from
present-day observations of paleosols is easily illustrated with an extinction event
occurring 33.9 myr (million years) ago during the transition from the Eocene to the
Oligocene. By the way, it was not a truly extreme event in the Earth's history even
if it is called Grande Coupure (Great Break). Cetaceans (such as a whale, dolphin,
or porpoise) were the main affected animals. The general cooling was accompanied
by climate phases documented by transitions from Entisols to Inceptisols and by the
upward shifting of calcic horizons.
Estimating the age of observed relics of past soils is a very important part of
studying paleosols. For the youngest paleosols, which evolved not earlier than
40,000 years ago, radiocarbon dating is commonly used. It is based upon the deter-
mination of the ratio of “ordinary” carbon
12
C to radioactive carbon
14
C. With the
top index denoting the number of neutrons in the carbon nucleus, we know that
12
C
has 12 neutrons and is stable. We also know that
14
C is not stable since it has 2 addi-
tional neutrons and is in a continual transition to eventually become stable, nonra-
dioactive nitrogen
14
N. Because the rate of
14
C decay is in equilibrium with the rate
of appearance of new
14
C created by cosmic radiation, the relative concentration
12
C/
14
C in the atmosphere is virtually constant. We say virtually constant owing to
the fact that minute oscillations of cosmic radiation occur. However, this slight
oscillation around its average value is negligible in our dating method. We are tak-
ing 1 atom of
14
C as related to 1 trillion atoms of
12
C. The same ratio of those two
isotopes exists also in living organisms, since this constant ratio enters into plants
due to photosynthesis. When atmospheric carbon forms organic molecules, the ratio
of the two isotopes is kept the same in the new organic molecule like in the atmo-
sphere and the same is valid for animals consuming the plants and the same happens
to plankton in waters. All living bodies on the Earth, including us,
Homo sapiens
,
have the concentration
12
C/
14
C in equilibrium with that in the atmosphere. The
decayed atoms
14
C in living bodies are replaced by the
14
C from the atmosphere. At
the moment of death of the animal or the plant, all metabolic functions stop and the
acceptance of atmospheric mixture
12
C/
14
C also stops. Because
14
C is not stable, a
slow decay is running and the atom
14
C is transformed into
14
N and a weak beta
radiation inside of the dead body. However, this decayed isotope
14
C inside of the
organic molecule is not replaced by the new isotope from the atmosphere since the
organism is dead and the earlier living functions have stopped. The consequence of
