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Re: Asteroid Impact Finally Confirmed



At 09:17 AM 3/10/97 -0600, Robert.J.Meyerson@uwrf.edu wrote:

>>B) How come lots of marine plankton (which assumably were the base of the
>>ocean food chain) went extinct, but horseshoe crabs, many fish and sharks
>>did not?
>
>For a variation of the above explanation.  Plankton suffered greatly, but how 
>did algae fare?  If some varieties of algae were to come through in good
shape, 
>they might be able to provide a solid enough nutrient base that would allow 
>relatively small animals to survive (I know this doesn't explain the Great 
>White lineage going through alright).

The coccolithophorids, one of the major photosynthesizing groups of
plankton, suffered a catastrophic decline at the K-T boundary.  Although
they are still present (at greatly reduced numbers), they were a huge
component of the later Mesozoic seas.

Coccolithophorids are covered with tiny plates of calcite, called
coccoliths.  When the plankton dies, the coccoliths disaggreate from the
tissue and accumulate on the sea floor.  If lithified, we call these
deposits "chalk".  Thus, coccoliths are where the Cretaceous (i.e., "the
Chalk") gets its name, and the loss of major chalk deposition was one of the
classic markers for the Cretaceous/Tertiary boundary.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661