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"Natural" atomic explosion in the Sahara

Flying goat raised this topic in a muddled  recollection.  My own
recollection is also muddled, but as I recall it was  a bit 
farther south in Africa than the Sahara.  The date was earlier
than 3 Ga.  It was not an explosion as such but rather a contained
nuclear reaction rather like an atomic reactor, continuing for a few
thousands of years.  This does not require partitioned isotopes of
uranium, merely a high local concentration.  


Someone asked me about the references for the date of the melt
rock oc Chicxolub.  I originally wrote from memory.  I have finally
found references.

The best reference is Carl C. Swisher and others (eleven of them)
(1992). Coeveal 40Ar/39Ar ages of 65.0 million years ago from
Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites.
*Science* 257,  14 August 1992, pp.954-958.  The same  issue of
Science also includes a more general editorial on p. 878.

Swisher and his crowd found a date for the glassy melt rock nearthe
base of the crater (1,390 to 1,393 meters below the surface) of
64.98 Ma plus/minus 0.05 Ma.  Glassy tektites from the K-T boundary
ejecta layer on Haita were dated to 65.01 plus/minus 0.08, and from
Arroya ek Mimbral, Mexico at 65.07 +/-   0.10 Ma.  These dates are 
statisti cally indistinguishable.


>From: David Brez Carlisle
bk090@Freenet Carleton.CA