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Downgrading the Chixalube Impact
Date: Fri, 2 Oct 1998 21:42:11 -0400 (EDT)
From: John Bois <email@example.com>
To: "King, Norm" <firstname.lastname@example.org>
Subject: Re:Norman MacLeod's opinion of Alvarez' dispassion
On Fri, 2 Oct 1998, King, Norm wrote:
> Walter Alvarez is a geologist. His father, Luis, was an astrophysicist.
Of course. Why else would he be fossicking for iridium all around the
planet. Sorry about that.
> I would say that a bolide is indeed implicated in the extinction. It is
> implicated by the apparent contemporaneity of the events (as go also
> pointed out).
> But is it the whole answer? That's another question.
> I think it is also true (but if anybody can dispute this statement,
> please do so) that there are no data relating the extinction of anything
> to any particular event, including matters of competitive interaction.
> We just think some connections are reasonable. So, it all boils down to
> what you are going to accept as a reasonable connection.
Right. But this is a "feeling". There is no confidence interval or any
such statistical test.
> You also can't
> _prove_ that smoking causes cancer.
People who smoke are more likely to get cancer. This is a reasonable
connection then. There are lots of thoroughly reliable data on that.
But there are none on dinosaurs and bolides. Indeed, there are data to
suggest dinosaurs were in serious decline
(from 32 to 19 genera in the last 10 million years) without the influence
of the bolide. Archibald says: "...recent studies show (the Chicxulub
crater) to be more on the order of 100 km across. This is the same size
as the Popigai Crater in Siberia, which was formed almost 36 mya, and
which appears to have been formed at the same time as the 80 km wide
Chesapeake Bay impact crater. Thus we have 100 and 80 km wide craters
that formed at the same time (within present margins of error) that caused
no identified extinction, while Chicxulub is supposed to have devastated
the world's biota."
While this is my last post on the Alvarez subject, I would like to
know if any other people here have heard of this downgrading of Chixculub
(from 180 km to 100 km.).
Haven`t heard of any "downgrade", but just got finished reading Chatterjee`s
book ..."The Rise of Birds", where he indicates an approximate 600 km
"Shiva" crater that he believes was concurrent with the Chicxalube impact.
He also indicates that small fragments of additional bolide strike (s) at
the K-T boundary were found in a drill core from Deep Sea Drilling Platform
576 in the western north pacific. All this indicating multiple strikes from
numerous bolides, all concurrent, and all lying in an apparently straight
line path circling the globe, which he terms the "Alvarez Impact Belt"! So,
it could have been very similar to the Shoemaker-Levy impact on Jupiter not
so long ago.