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Re: multiple bolide impacts

>The Deccan Traps flows date from 66 mya. The crater below Mason (?) Iowa
>(long since filled in by glacial debris) is also dated to 66 mya. Of course,
>the Chixulub crater is dated to 65 mya.

Updating you about recent discoveries, the Manson crater is very well dated
at the mid-Campanian, millions of years older than the K-T boundary.

>   In the geological record, there are numerous multiple impact records,
>including three craters in Siberia dating to 2.5-to 2 mya. These may not have
>been simultaneous but may have fallen periodically over some 10s or hundreds
>of thousands of years.
>   Could then the K-T boundary be, in reality, a phenomenon that was some one
>or two million years in the making or perhaps 10 to hundreds of thousands of
>years in the making? Granted the Deccan Traps can be attributed to the
>pulling away of the Seychelles from India 66 million years ago, but could
>that rift have been triggered by a bolide impact?
>    And could that impact have coincided witht the Mason Iowa event and
>perhaps other smaller impacts?
>   And could the Chixulub impact be related to all these events? I ask this
>in light of the continuing debate over the decline of dinosaur species and
>families before the K-T and with the disappearance of many marine reptile
>families several million years before the coup de grace.
>   The Deccan Traps volcanic episode (one of many in the geologic record)
>lasted perhaps 100,000 years and may very well have stressed marine and
>terrestrial environments to the point that researchers see declines in
>families in the fossil record in the latest Mastrichian. The declines would
>have leveled off once the volcanism finally subsided, but there was too
>little time for family or species rebound before the Chixulub event.
>    The more information that comes to light about Chiculub, Mason Iowa, and
>the Deccan events, the more I suspect multiple extra-terrestrial agents -
>perhaps a comet or asteroid "storm" - moving through earth's orbit over the
>course of two or three million years.
>   Does anyone have an opinion on the likelihood of such a senario?

The "meteor swarm" idea has been tossed around by many individuals.
Basically, the thing that's needed for such events would be a massive, dark
object a few hundred or thousand AU (astronomical units = 93 million miles)
out.  Such a dark object (Lucifer if you like Niven & Pournelle, Nemesis
for most everyone else) would periodically come close enough in system to
shake a few thousand comets out of orbit (thousands would be needed if you
expect multiple impacts on a little dustspeck like home...).

No dark object of this sort has yet been identified.  One way to really
support this idea would be finding impacts of similar dates on other solar
system objects; one problem with the idea is that, to get an iridium spike,
you need an asteriod rather than a comet.

Thomas R. Holtz, Jr.                                   
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092