Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site pyuxt.UUCP Path: utzoo!watmath!clyde!burl!hou3c!hocda!houxm!mhuxl!ulysses!gamma!pyuxww!pyuxt!marcus From: marcus@pyuxt.UUCP (M. G. Hand) Newsgroups: net.physics Subject: Re: Reversing of Magnetic Poles Message-ID: <128@pyuxt.UUCP> Date: Mon, 4-Jun-84 23:02:47 EDT Article-I.D.: pyuxt.128 Posted: Mon Jun 4 23:02:47 1984 Date-Received: Wed, 6-Jun-84 05:50:12 EDT References: <1458@seismo.UUCP> Organization: Bell Communications Research, Piscataway N.J. Lines: 22 So, geophysics - something at last that I as a geochemist can reply to. However, on this occasion i would do best to point out that the frequent reversals in the earths magnetic field have taken place over significant periods of time even by geological time scales, and then point you to the Scientific American of September 1983, which ought to become a 1st year geo-sciences set text book. (Geological time scales tend to be relatively inaccurate because of the imprecision in measuring a set point in time. Relative times may be fixed using geologically instantaneous events - volcanic erruptions, both lava and dust layers, turbidity currents, then things like ice ages and magnetic reversals which take place over a significant but short length of geological time, and later on we get to floral and faunal changes and extinctions, whose duration, as the age increases becomes less significant as a proportion of absolute age. Radio active dating still has a number of serious problems resulting from biological preference for different atomic masses, potential partioning of atomic masses through statistical thermodynamics of magma differentiation over geologic time scales, potential isolation and separation of magmas, contamination with country rocks, ..... this is not to say that they are no good, but simply that one must be prepared to justify ones assumptions and that there may be a number of different angles of attack.) Marcus Hand (pyuxt!marcus)