> On Wednesday, October 03, 2001 9:51 AM Mike Lorrey firstname.lastname@example.org
> > If moons were not so important, Venus would have beaten us in the
> > civilization game. Venus was once in a cool greenhouse stage earlier
> > than earth was, and if earth did not have its atmosphere and lithosphere
> > stripped by planetesimal impact and resultant sequestration of 98% of
> > its atmosphere, the Earth would be just like Venus right now.
> I've heard this view mentioned before. Does anyone know of any articles in
> the scientific literature on it? I'd like to read more about it.
There was a good post several months ago on this list linking to an
article on the argument. I also recommend Martyn J. Fogg's seminal
textbook "Terraforming: Engineering Planetary Environments", which I
think should be on the reading list for all Extropians.
Originally, the Earth had about 50 times the atmosphere it has right
now, and a crust thicker than that of Venus. About 3.5 billion years
ago, a planetisimal glanced the earth, remelting its crust while
launching most of it into orbit around the earth, eventually
agglomerating into the Moon. Prior to this, the earth had no tectonic
system. With a thick crust, the earth had a slow percolation system like
Venus. Only when most of the crust was blasted away into space was a
plate tectonic system able to develop.
Similarly, prior to the formation of the moon, the earth had a far
weaker magnetic system that relied on the thermal convection currents of
the inner earth to generate asymmetric fields of varying strength around
the earth. It was only when the tidal drag of the moon on the earths
rotation occured that the current rotor-stator system of the core/mantle
system began to generate the preponderance of the magnetic field we have
today. The fact that the rotational and magnetic north poles both
precess is evidence of this.
The planetesimal impact blasted a good portion of the earth's early
atmosphere into space as well, and enough dust into earth orbit to
significantly cool the earth enough to allow life to form without
incineration. With life, the CO2 predominant atmosphere became
sequestered over time and is now the vast layers of limestone that
underlie much of the continental plates.
Life could never form today on Venus, as even the most basic bacteria
would incinerate many kilometers above the surface. When the sun was
significantly cooler several billion years ago, this was not the case.
At the time that Venus was broadly hospitable to life, the earth was in
its 'Ice House' stage, where life only existed around volcanic vents and
within the very rock of the earth. As the Sun warmed over time, Venus
eventually became inhospitable, and any life that may have evolved was
never able to develop any technology due to its thick lithosphere.
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