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three impacts at the K-T boundary



>In light of the comet or asteroid impact on Jupiter, it seems plausible that
>the K-T boundary is the tailsman of a multiple impact on earth.
>   The Deccan Trap flows in India date from 66 million and, according to some
>recent publications, the flows overlay sediment littered with shocked quarts.

Not entirely true.  The Deccan Traps are a series of flows, interbedded
with sedimentary layers of both Cretaceous and Tertiary age.  Thus, the
flows began well before the end of the Cretaceous, and continued until much
later.  Unless the impact traveled backwards in time, the initiation of the
Deccan Traps was not due to the terminal Maastrichtian impact.

>   The Chixulub crater off the Yucatan is dated to 65 million and is, of
>course, associated with shocked quarts and tsunami rubble throughout the
>Caribbean.

Although there is some debate about the age of Chicxulub (Meyerhoff et al.
1994), this is the only good potential K-T impact site known.

>   The long eroded and filled in crater in Iowa also dates from 65 mya.

Most certainly not!  See Izett et al. 1993 (I'll look up the full reference
but it was in one of last year's issues of Science).  Radiometric,
biochronologic, and good old fashioned stratigraphic dating techniques all
point to a mid-Campanian date (i.e., 12 my before the K-T boundary).

>   Perhaps the earth was bombarded, much the same way Jupiter was, with
>direct impacts in both North America and Asia, creating direct effects on
>those continents and, of course, indirect long-lasting effects worldwide.
>   Any thoughts on the potential for multiple impacts?

For one thing, the terminal K-T boundary event had to include at least one
asteroidal (as opposed to cometary) impact - there is no evidence of
sizable amounts of metals in comets, while there is good hard evidence of
high concentrations of iridium in iron meteorites.  Nevertheless, multiple
impacts would certainly be more effective than a single strike in stressing
species to extinction.

An additional thought - consider the scale of some of the Jupiter strikes. 
Many of them were vastly more powerful than anything which struck during
the Phanerozoic (540 Mya to the present).  If just one of the larger of
them had struck the Earth, it would have produced a crater which extends
from Washington, D.C. to New York City, and probably have boiled the oceans
to a vapor in the process.  So much for multicellular life...

So remember what David Gerrold has said about Mother Nature:

Mom's a bitch!

                                     
Thomas R. Holtz, Jr.
Vertebrate Paleontologist in Exile
U.S. Geological Survey
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092

email:  tholtz@geochange.er.usgs.gov 
Phone:  703-648-5280
FAX:            703-648-5420