Re: EVOLUTION: Stress needed for diversity?

From: Michael S. Lorrey (
Date: Tue Mar 21 2000 - 21:29:33 MST

Technotranscendence wrote:
> On Tuesday, March 21, 2000 9:11 AM Billy Brown wrote:
> > I don't doubt that complex organisms capable of surviving such
> environments
> > are possible, but I have some reservations about the idea that they could
> > evolve locally. Before you can have organisms with lots of elaborate
> > adaptations for surviving extreme environmental swings, you have to have
> > simple organisms that don't have such adaptations. You need an
> environment
> > in which life can arise, solve the basic survival problems like energy
> > production and reproduction, and reach a level of complexity that allows
> > complex adaptations to evolve. That implies that a world that has a
> stable
> > period followed by wild climate swings may support interesting life, but
> one
> > that has always had extreme shifts may not evolve life in the first place.
> While I agree with what Billy is saying here for the most part, Earth is not
> as tame as some might think. Even now, some climatists have proposed that
> the Earth has completely frozen over several times in its history and that
> rapid climate change followed by stable periods might be the rule. (See
> "Snowball Earth" by Paul F. Hoffman and Daniel P. Schrag in _Scientific
> American_ 2000 Jan for the former (now at
> and "Rapid Climate
> Change" by Kendrick Taylor in _American Scientist_ 1999 July-August.) This
> is by no means like a highly elliptical orbiting planet scenario, say, of
> Poul Anderson's _A Circus of Hells_, or the OnOff Star scenario in Vernor
> Vinge's _A Deepness in the Sky_, but it should give one pause.

Actually, the basis of the earth's deep freeze occilations were due to
the travels of the continents. With most continental areas on the
equator and periods of heavy vulcanism, such periods were a natural
consequence. During this period, antarctica was not at the south pole,
so it was not sequestering 3/4+ of the ice on the planet. No land locked
ice cap meant sea levels 200 meters higher than they are now. Higher
pressure at the bottom of the ocean allowed greater sequestration of
methane hydrates under the ocean floors, and thus less methane in the
atmosphere(methane is about 6x more effective as a greenhouse gas) The
loss of methane causes a cooldown, increases in ocean ice caps, and
glacial buildup, the vulcanism of the newly spreading continents kept
the dust levels high. The CO2 concentrations and global climate
temperature are linked only by a log relationship, such that CO2
concentrations variances at low levels have wide impact on temperature
fluctuations, but as concentrations increase, this effect falls off.
According to my geologist cousin, essentially if we dropped the
atmospheric CO2 levels by 50%, we'd drop global temps by 20-30 degrees,
while if we increase them by 50% from the current levels, global temps
will go up by less than 5 degrees.

According to Drew, the antarctic ice cap (the large one, not the small
one on the coast) is stable over the long term, and its been that way
since the last major extinction/possible impact period of 22 million
years ago. The winds flow outward from the cap (the catabatic winds),
and are replenished from cold upper atmospheric air that drops down from
high altitudes (and the higher altitudes are cooling down while the
surface levels of temperate climates is warming up.) The Greenland ice
cap may collapse, and the arctic ice cap will most likely vanish in a
few decades. If the Greenland ice cap collapses, it will result in sea
level rises of 3-9 meters at most. If only the arctic ice cap melts
away, there will be little or no sea level changes, because that ice is
already floating in the water. Any rise will simply be due to thermal
expansion of the oceans.

Mike Lorrey

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