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From: guy@slu70.UUCP
Newsgroups: sci.bio,sci.astro,sci.misc
Subject: Re: Mass extinctions
Message-ID: <11@slu70.UUCP>
Date: Tue, 31-Mar-87 10:07:15 EST
Article-I.D.: slu70.11
Posted: Tue Mar 31 10:07:15 1987
Date-Received: Sat, 4-Apr-87 07:32:08 EST
References: <784@scicom.AlphaCDC.COM> <1522@husc6.UUCP>
Organization: St. Louis Univ., St. Louis, MO
Lines: 13
Xref: utgpu sci.bio:205 sci.astro:782 sci.misc:236
Summary: reversal periodicity

In article <1522@husc6.UUCP>, gallagher@husc4.HARVARD.EDU (paul gallagher) writes:
> some single ultimate cause, but there are "no obvious terrestrial or solar
> processes operating cyclically on time scales of 10^6 to 10^7 years", except
> for the unproved hypothesis of periodic magnetic reversals.  So the ultimate
Not only is this hypothesis unproved, there are excellent reasons for believing
it to be untrue. Careful statistical analysis of the reversal record shows
no periodicity whatsoever. The probability of reversal is best modeled as
a completely stochastic process (although there are gradual changes in the
reversal rate). See "The Earth's Magnetic Field" (Merrill and McElhinny)
for more details and citations.

Your friendly geophysicist,
                Guy M. Smith