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RE: well-lit dinosaurs



Title: RE: well-lit dinosaurs
At 10:42 AM -0500 3/2/01, Thomas R. Holtz, Jr. wrote:
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of Gavin Rymill
>

>This is only tenuously a list topic but the BBC website still managed to make it a dinosaur headline!!
>
>http://news.bbc.co.uk/hi/english/sci/tech/newsid_1196000/1196652.stm
>
>Still interesting though.
>
Cool stuff.  Apparently preliminary data suggests that the Earth's magnetic field during the Long Cretaceous Normal (C34n, running from the lower Aptian (c. 120 Ma) to the beginning of the Campanian (c. 83.5 Ma)) was three times the present intensity.
 
This mid-Cretaceous is an interesting time for a number of (quite possibly interrelated) reasons:
 
*Highest sea levels since the Cambrian (at least), making it the highest in post-Pangaean history
*Higher activities of the mid-ocean ridges
*Faster rates of sea-floor spreading
*Extremely low temperature gradient from equator-to-pole (that is, climate at the equator and climate at the poles were very similar, and hot)
*Greater total separation of landmasses than at present, due to the net effects of plate tectonics and oceanic highstands
*REALLY big South American and African dinosaurs
*Fins, fins, fins, fins...
*Arrival of Asian-style dinosaurs into the Western Interior of North America (latest Albian/earliest Cenomanian)

Yes. And as for the magnetic declination and magnetic field during the Cretaceous (and other times), then:

I think this depends on where the rocks "were" when they got magnetized and especially what their "altitude" was when they got magnetized. If they were down deeper and "sent" by tectonics to "higher" levels that could cause a greater B field (closer to the loop currents).  If during a flip period, it might be possible to have local anomalous high fields.  Also if "rocks" are squeezed this would force the magnetic lines of force to appear closer together (thus appear like a greater intensity field).

Remember F = qE + (v X B) were B is the magnetic field intensity.

F is the total electic + magnetic force
E is the electric field
q is the charge of the particle
v is the velocity of the charged particle
A compass lines up along a B field direction, since the NORTH MAGNETIC POLE OF THE BAR MAGNET seeks out the opposite MAGNETIC POLARITY... the magnetic pole in Northern Canada.  North magnetic pole of the compass is the point, south magnetic pole is the feathers of the arrow.

B is generated by the loop currents in the molten core... loop current  generates a three D magnetic dipole pattern.

Just my paleodeclination thoughts for the day.

:-)
Cheers, (Fridayfridayfriday)
Marilyn W.
--
                     =00=  =00=  =00=  =00=
                  Marilyn D. Wegweiser, Ph.D.
             Adjunct Curator of Vertebrate Paleontology
                   Cincinnati Natural History Museum

Assistant Professor of Geology
Department of Geology                     mdwegweiser@bsu.edu
Ball State University                        Office: 765-285-8268;765-285-8270
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