Russian Journal of Earth Sciences
Vol. 4, No. 4, August 2002
One-way and quasi-periodic climate changes:
Geologic evidence
N. M. Chumakov
Abstract
During the last three billion years, the Earth has been experiencing a slow global
cooling, expressed in the progressively increasing frequency and scale of glacial
events.
Based on these indications, geologic history can be divided into three climatic stages:
(a) non-glacial (Early and Middle Archean), (b) with episodic glaciations
(Late Archean to
Middle Riphean), and (c) with frequent periodic glaciations (Late Riphean-present).
The
cooling has apparently been caused by changes in the density and composition of the
atmosphere, by the waning of heat flow from the Earth's interior, and by an increase
in
the planet's albedo in response to continental growth. The irreversible climate trend
was
modulated and obscured by numerous superposed temperature oscillations of varying
periodicity and amplitude. A broad spectrum of such oscillations, from ultralong-term
(a
few hundreds of million years) to decadal-scale, have been established. The Phanerozoic
exhibits a hierarchy of coordinated periods of climatic oscillations of 10-12 ranks.
Climatic oscillations of the first two or three ranks are to be detected in Proterozoic
glacial sequences. In light of the above, the Earth's climate history appears to
be
naturally determined, the slow irreversible cooling of the Earth's surface being
superposed by a rather regular pattern of periodic oscillations. The inference suggests
itself that the Earth's highly complex and open climate system has been rather close
to a
stationary state, and that among the multitude of nonlinear processes bearing on
climate
there were a small number of those most influential, "governing" processes with periodic
attractors. Glaciation maxima preceded principal tectonic phases, and they are clearly
correlative to suprasubduction volcanic maxima, whereas the periods of degradation
or
cessation of glaciation coincide with tectonic, granitization, metamorphic, and,
occasionally, mantle-plume volcanic maxima. This suggests that onsets of glaciation
were triggered by explosive volcanism and by the ensuing volcanic winters.
Deglaciations must have been due to increases in atmospheric transparency, to carbon
oxidation and partial decarbonatization in sedimentary sequences of orogens, and
to
pulses of mantle plume volcanism. A similar explanation applies to long-term climatic
oscillations that lasted 30 m.y. on average. Short-term climatic oscillations are
explicable
by variations in the astronomical parameters of our planet, and ultrashort-term ones,
apparently, by solar activity variations.