chris@umcp-cs.UUCP (06/03/84)
I haven't heard anything about ``will'' flip, but the Earth's poles
have reversed in the past. Evidence on/in rocks from the Atlantic
sea floor, near one of the crust plates [sorry if I'm getting words
wrong; my tectonics is rather rusty], shows that they have reversed
more than once before.
Chris
--
In-Real-Life: Chris Torek, Univ of MD Comp Sci (301) 454-7690
UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris
CSNet: chris@umcp-cs ARPA: chris@marylandflinn@seismo.UUCP (E. A. Flinn) (06/03/84)
|>>I have heard rumor that in the year 2000 (+ or - a few years) |>>the magnetic poles of the earth are going to do a flip-flop. |>>Is this only a rumor or is there some truth to it? No and yes. The strength of the geomagnetic field has been decreasing almost linearly for many years. The measurements made by Magsat in 1979 confirmed that *if* this linear decrease continues, the field strength will vanish in about 1100 years from now. Other changes are also taking place - the non-dipole components of the field are changing, there is the well-known westward drift of the geomagnetic field, and the inclination of the dipole component is gradually changing. |>>If it is true, is it going to be a gradual change of polarity or rapid? Gradual, if the linear trend continues. The field has reversed direction many times in geological history, so presumable the field will keep on changing, the north and south poles having changed identity. |>>What impact might it have on our magnetic shielding from |>>solar radiation? There is no evidence for species extinctions at the previous times of magnetic reversals, so it seems unlikely that life on earth would be profoundly affected. We will be bombarded by the solar wind for a few hundred years, and I haven't seen any discussions of the environmental implications of this sort of thing. -- Ted Flinn
marcus@pyuxt.UUCP (M. G. Hand) (06/05/84)
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)