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From: thomas@bnl.UUCP
Newsgroups: sci.bio,sci.astro,sci.misc
Subject: Re: Mass extinctions
Message-ID: <91@bnl.UUCP>
Date: Fri, 10-Apr-87 09:25:10 EST
Article-I.D.: bnl.91
Posted: Fri Apr 10 09:25:10 1987
Date-Received: Sun, 12-Apr-87 05:45:02 EST
References: <784@scicom.AlphaCDC.COM> <1522@husc6.UUCP> <11@slu70.UUCP>
Organization: Brookhaven National Lab. Upton, N.Y.
Lines: 39
Xref: utgpu sci.bio:271 sci.astro:831 sci.misc:243

> 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

In Physics Today, February 1987, p. 17, there is a report on "Do asteroid
impacts trigger geomagnetic reversals?" which is based on an article by
Richard Muller and Donald Morris in Geophysical Research Letters, November,
1986, p. 1177.
   Their coupling of extraterrestial impact to geomagnetic reversals predicts
that abrupt climatic change should occur at the same time.  Supporting
evidence has recently become available from discoveries by R. V. Krishna-
murthy and coworkers at the Ahmedabad Physical Research Laboratrory in
India.  (Nature 323, p. 150, 1986.)  Quoting:
   The Karewa plateau in the Vale of Kashmir was once a vast lake.
   The geomagnetic reversals of the last few million years are
   precisely documented in the magnetostratigraphy of its deep
   sediment, now conveniently exposed.  Examining the carbon-nitrogen
   ratio of the organic component of this same sediment, Krishna-
   murthy and company found striking, narrow peaks rising an order of
   magnitude above background at precisely the times (depths) of
   three geomagnetic reversals, including the most recent.  The
   nitrogen concentration is taken to be a measure of the protein-rich
   plankton and algae population of the lake water.
 The Physics Today article is a "news" report, so it is quite readable even by
those who are not experts in this area.  It also quotes some skeptics near
the end of the article.

                                         Richard A. Thomas
                                         Brookhaven National Lab