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Re: Impacts and ETs




How be it earth is cooling in such places as California?   It seems to
suggest, liken the time of dinosaurs, that earth will again shift its
axis.

Albert B. Franklin

This one is actually pretty much on topic!

The term global warming refers to the overall average temperature based on the mean between the highs and lows taken over many data collecting points around the globe. (N is huge). Berkeley's new cooperative computing project using BOINC is projecting big global increases over the next century. 1998 was the hottest year on record with 2002, 2003, 2004 being the next 3 in order. 2005 is setting up to be warmer than 1998. Having said that, it has been warmer in the past and the Mesozoic (dinosaur's time) was one of those warmer periods. The earth's axis wanders gradually over time as the planet wobbles but this is not a rapid phenomena. Known as the Chandler Wobble, the crust of the earth floats around over the hot liquid mantle of the earths deep interior in an immeasurable slow process. This is not to say that it has to be a slow phenomena. These two issues are not directly linked on a short term basis or to put it simply....Global warming (or a cooling California) as a result of greenhouse gasses will not cause polar shifts. The latter could however change the temperature because of the effect causing a change in atmospheric circulation patterns in some cases but this is not the case today as the Chandler Wobble (though variable in it's rate to a small degree) is sitting on it's 140 year measured average since 1998. The root cause of polar wanders is baseline tectonic movements effecting the rotation so significant tectonic changes can certainly change climate but not so much visa versa.

To relate this back to the Mesozoic, the source of the discussion below is. http://www.mala.bc.ca/~earles/news.htm

In a year 2000 paper published in Science, geologists from Texas A&M University and the Scripps Institute in California have suggested that there was a 16 to 20° shift in the earth's rotational pole at around 84 m.y. ago.

The theory is based on magnetic data from 27 Pacific seamounts. The data show a fairly typical "apparent" polar wandering curve (related to continental drift) for the period from 125 to 39 m.y. - but there is evidence of a major jump in the pole position at around 84 m.y. The authors can't yet pin-point the time of the shift, but they suggest that it might have taken around 2 m.y. to complete - which implies a rate of change of just over 1 metre per year - roughly ten times faster than the fastest plate motion rates. They suggest that the shift resulted in a change in the earth's spin axis caused by a movement of mass either on or within the earth.

A spinning earth, like any other spinning object, is most stable when most of its mass is as far away from the spin axis as possible (ie. close to the equator). If a large mass moves towards one of the poles there will be a tendency for the object to roll to bring that mass back towards the equator. In the case of the earth, the spinning axis will still be pointing towards the same stars in space, but the pole location will be a different point on the surface.

The displacement of mass required to cause such a shift could be related movement of plates, or to a change in the distribution of material within the mantle. The authors of the paper in Science suggest that the latter is the most likely case, and they point to the end of the Cretaceous long-normal superchron (where the number of magnetic reversals per million years dropped to zero and lasted from about 110 mybp to 83 mybp), at 83 m.y., as evidence that there was a major reorganization of the mantle at this time.

One possible trigger for a major change within the mantle is the disposition of subducted oceanic slabs. It is predicted that the phase change in mantle mineralogy at a depth of around 660 km could affect the buoyancy of subducted slabs, and that in some cases the slabs may get "hung up" in this region, and then break through en masse - abruptly shifting the distribution of mass within the earth.

References

Sager, W. and Koppers, A., , Late Cretaceous Polar Wander of the Pacific Plate: evidence of a rapid true Polar Wander, Science, V. 287, p. 455-459 (January 2000)

Kerr, R., Did the dinosaurs live on a topsy-turvy earth?, Science, V. 287, p. 406-407 (January 2000)

Frank Bliss
MS Biostratigraphy
Weston Wyoming

On Feb 13, 2005, at 9:42 AM, Albert Franklin wrote: