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k/t "bone spike"

If the impact occurred and caused the acid rain suggested by the modellers
it is not hard to see why a bone spike would be the last thing that you
would expect to find.  Consider for a moment the boundary clay.  What ever
produced that had to erode many rocks to produce that clay everywhere we
see the boundary.  That sort of erosion implies very large quantities of 
very acidic water falling out of the sky.  Now consider the average bone.
It will dissolve within an hour if put into 6M HCl.  Put it under water
in water that has a pH < 6 and it will dissolve within 1 week to 1 month
depending on the size of the bone and it's bone type (relative % of compact
to cancellous bone important here).  The acid rain falling under the 
K/T impact model scenario is more than sufficient to destroy any bone
on the surface within a short period.  Moreover, the water would have
also penetrated the upper soil zones.  There combined with bacteria
( who can survive very acidic conditions!) would have produced even
more acidic water (just as occurs today in many soil zones) because
of the dead vegetation and animals.  That would have been capable of
dissolving the calcium phosphate from any bones in the active vadose
zone.  Even bones in the upper phreatic zone might have been affected
because the upper groundwater table likely would have become acidified
also.  This sort of geochemical scenario can also explain why few
bones (if any??) have been found just below the K/T boundary. 
(Correct me there if I am wrong Tom/George/....)
The only bones not likely to have been severely affected by such 
events would be those that had already been remineralized to silica,
which is a process that normally takes a long time, and would not
likely have happened to bones less than 100 ka to maybe 10 Ma (at 65 Ma).


Bonnie A.B. Blackwell,                          bonn@qcvaxa.acc.qc.edu
Dept of Geology,                                off: (718) 997-3332
Queens College, City University of New York,    fax: (718) 997-3349
Dept of Earth \& Environmental Sciences,        fax: (718) 997-3513
The Graduate Center, CUNY,                      messages: (718) 997-3300
Flushing, NY 11367-1597