On Mar 19, 4:08 am, "Raymond W. Arritt"
<[email protected]> wrote:
> Alastair wrote:
> > Yes, I gave you a bum steer referring to grasses. What I should have
> > said was that the evolution of the C4 pathway could have been the
> > cause or a contributing factor leading to the current Pliestocene ice
> > age.
> >http://en.wikipedia.org/wiki/C4_carbon_fixation
>
> The C4 mechanism confers an advantage at low CO2, so it's more likely
> that changes in C4 abundance during the Plasticine were driven by
> fluctuations in CO2 than the other way around.
>
> -rwa
If the drawdown of CO2 since the Cretaceous was due to plants, then C4
plants would be able to survive and continue the drawdown at lower
levels of CO2 than C3 plants. In other words, until the C4 plants
evolved, the lowest level of CO2 that could be achieved would be the
minimum required for C3 plants to survive. With the evolution of the
C4 plants that minimum level became much lower.
It is more complicated than that, with vegetational sequestration of
CO2 being only one leg of an interwoven carbon cycle, but it does
provide a limiting value.
Cheers, Alastair.
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