RE: NS reversals

[brian whatcott <inet@intellisys.net>]

At 13:17 5/6/98 -0600, you wrote:
> Does anybody if there has been any attempts to correlate the reversing 
> events, when there must be a period of "randomized" field, with speciation? 
> I suspect that the time scales may be grossly different, just curious.
> ...
> Joel Rauber

My (not extensive) reading suggests that geomagnetic field reversal is an
'instant' event as judged by the geological record.
 You will recall that the successful plate tectonics theory drew convincing
support from the field reversal record provided by trawling along the
orogenetic track from oceanic bed samples.
 In addition, a standard sampling method is to mark a terrestrial rock
sample's orientation, then core it out with a diamond hole saw.
 These techniques can hardly distinguish a thousand year difference in
general,
so that is how long a 'geological' instant may be.

   But it is well to say something about speciation. This is naturally tied
to cycles of generation - the principal avenue for assortative coupling of
characters. There is a large variation in time-scale involved here:
students may personally witness the evolution of say drug-resistive
characters in bacteria, or perhaps differentiated morphology in fruit-fly,
but they will hardly hope for noticeable (fixed) change in domestic animals
such as horse or cattle whose world-wide commonality of bred-in features is
obvious - but pursued over longer-than-human lifetimes.

 I think of the "arab" horse and the Guernsey, Jersey, Aberdeen-Angus,
Hereford cattle whose British placenames memorialize their ancestry. One
can argue that such an environment was conducive to a theory like
'Evolution by Natural Selection'. The evidence of differentiated cattle,
pigs, sheep, horses, dogs, cats and plants was all around. (Where folks
have lived more transient lives and selective breeding is less obvious, one
might argue that religious beliefs which stress one time creation of
species are more acceptable.)

At any rate, to answer Joel's question - if we surmise that a
field-reversal and the associated U-V and other radiation intensifications
last a thousand years, we might expect most change in the species which
leave the scantiest traces (geologically).

Whatcott     Altus OK