"Robert J. Bradbury" wrote:
>
> Mike wrote:
> > Very interesting, and corroborating my earlier statements about large
> > moons being necessary for intelligent civilizations.
>
> Mike, I believe you are making at least one unsubstantiated leap.
> The development of "intelligent civilizations" would appear to
> depend in large part to the "rate" of evolution from simple
> organisms to higher organisms.
Yes, and which exhibits greater evolutionary rates, land or sea
organisms?
I didn't say 'intelligent organisms' because this would be entirely
possible with waterworld planets (as we see so plainly with dolpins,
whales, octopi, etc). If the waterworld scenario holds, there would be
so little land available for land life, and most of that would be
heavily volcanic, and thus subject to high rates of cataclysmic
extinctions, far higher than would be beneficial to evolution toward
intelligence.
A species that evolves intelligence in water will never get beyond the
stage of harnessing fire for obvious reasons, unless it migrates to
land, and then is limited by the cataclysmic behavior of supervolcanos
that are the norm with thick crust worlds.
> The existence or lack of existence
> of large moons may effect the geology and length of the liquid
> water period of a planet, but there is very little evidence
> (since we only have 1 data point) regarding the relation between
> those phenomena and the evolution of intelligence. We know for certain
> that the mutation rate for an organism can vary over a wide range
> (contrast HIV with Deinococcus radiodurans). Constraints on mutation
> rates for higher level organisms are far from certain. The most
> recent evidence from comparisons between the Mouse & Human genomes
> suggests that factors that influence gene duplication and successive
> adaptations may play a key role in the rate of evolution. So
> the development of intelligence may depend on two quite different
> genetic mechanisms (gene duplication & gene mutation rates) which
> may be independent of each other and have a very wide range of
> possible values.
Also consider the prime points of my own argument, that did not focus on
the crust thickness issue that much. I focused on the magnetic field
phenomenon, where the tidal drag induced by a large moon induces a
differential rotational speed between inner and outer planetary layers
to generate a dynamo. A waterworld planet without a large moon would
have no magnetic field strong enough to protect it against cosmic rays
and radiation from its sun, so what land that did arise from
supervolcanos would be pummelled not only by constant volcanic activity,
but severe UV and other deadly levels of radiation. Thus any intelligent
species that did arise in the seas would not be able to migrate to land
without technology to protect it from radiation, but if it does not
migrate to land, it will never develop technology in the first place.
>
> Geologists & astronomers can make all the arguments they want to
> about "Rare Earth's" and while those arguments will be interesting
> they are not "trump cards" because biology can compensate for
> a very wide range of environmental variables.
We would need to see evidence that life can thrive alone on islands that
are not only volcanically unstable, but bombarded by high radiation
levels due to lack of a magnetic field. If you can come up with a
possible scenario for such, I am all ears.
This archive was generated by hypermail 2b30 : Fri Oct 12 2001 - 14:39:48 MDT