OLSEN, Paul E., Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY 10964.
Much recent work points to chemical weathering of continental
silicates as the principal control of atmospheric CO2.
Presently, chemical weathering is mediated by plants. Vascular plants increase
chemical weathering by drastically increasing acid leaching through respiration,
decay, and microbial symbionts. Through the Phanerozoic the continuing
evolution of terrestrial plant communities must have had a major effect
on weathering rates. However, the efficacy of plant-induced-weathering
is decreased by herbivory, which in turn decreases the invasion of soil
by roots and leads to increased physical weathering. There is a dramatic
correlation between the appearance of major plant trophic, reproductive,
and defensive innovations, increased terrestrial organic carbon burial,
and the onset of "ice house" conditions (presumably caused by decreased
CO2). Conversely, there is also a correlation
between the appearance of major herbivore inroads on terrestrial plants
and global "hot house" conditions presumably resulting from higher CO2.
I propose that the major "ice house"--"hot house" cycles of the Devonian-Quaternary
were caused by the lag between plant innovations and complete compensation
by herbivore-detritivore response. In this way, it seems possible that:
1) the Carboniferous coals are a consequence of limited herbivory and soil
litter decomposition and the Permo-Carboniferous glaciations were caused
by dramatically increased chemical weathering caused by the previous global
spread of vascular plants; 2) the Mesozoic "hot house" was brought on by
massive increases in megaherbivores and litter decomposers; and 3) Cenozoic
cooling and Quaternary glaciations resulted from the spread of herbaceous
angiosperms and most recently grasslands. Our own superherbivory, if continued
for tens of millions of years, will bring us back to mid-Mesozoic "hot
house" conditions, not by the burning of fossil fuels, but rather by a
global increase in physical over chemical weathering.
Geological Society of America, Abstracts with Programs,
v. 25, no. 3, p 71