Re: Impacts and ETs

[frank bliss <frank@blissnet.com>]

> 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:
>