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Re: craters and the k/t
Date: Fri, 6 Sep 1996 01:40:12 GMT
From: Brian Pickrell <firstname.lastname@example.org>
Subject: Re: craters and the k/t (Norm King)
Frank Crary (fcrary@rintintin.Colorado.EDU) wrote:
: In article <Dx85Hz.6vIemail@example.com>,
: Henry Spencer <firstname.lastname@example.org> wrote:
: >>Have you come across any discussions of the possibility of a chain of
: >>craters being associated with the k/t event?
The recent event on Jupiter is probably not a good model for Earth
impacts; Earth has a much weaker gravitational field than Jupiter, and is
less likely to either break up a nearby comet or capture all the pieces
: >The idea is not ridiculous, but it tentatively appears to be wrong --
: >the K/T event has been fairly solidly identified with the Chicxulub [sp?]
: >crater, which appears to be a single crater.
: I'm not so sure about that. [...] Given the
: difficulty of identifying the K/T event, after all those years
: of errosion, it's certainly possible that it produced a chain
: of craters which are either small and not yet identified, or
: which have been completely destroyed by errosion.
It's quite possible for a crater to erode away and leave no traces.
Most large, old impact sites which have been identified on Earth have
eroded so much that there is no trace of the original crater at all--the
crater and the rock it was in are completely gone. What remains is the
pattern of fractures in rock that was originally far beneath the crater.
That's what the Chixculub (?) structure is.
So it's possible that this crater was accompanied by others that aren't
there any more, but the odds are against it. What percentage of the
craters on the Moon or Mars are members of crater chains? I don't know,
but I think it's pretty small.
- If it won't go with a sledgehammer, don't force it.
Date: Fri, 6 Sep 1996 13:53:31 GMT
From: William Wiesel <email@example.com>
Subject: Re:craters and the k/t(Norm King)
Before the discovery of the Chicxulub (I checked the spelling) impact
site, attention focused on the Manson impact structure in the USA. This is a
35 km crater located at 42 deg north, 96 deg west, and dates to 65.7 +- 1 Myr:
indistinguishable from the K/T boundary. (see Richard Grieve, Meteoritics,
vol 26, pp 175-194, 1991. This is the "crater catalog".)
The problem with Manson was that it is too small to be "the" K/T impact
site. But since it is on the hemisphere of the earth centered at Chicxulub,
it could well be the impact site for the Chicxulub asteroid's satellite,
assuming that it did have one. I can't think of any way to test this idea,
These are my own personal opinions, and do not necessarily
represent those of the Air Force, Department of Defense, or U.S.
William E. Wiesel ph: 513-255-6565 ex 4312
Professor of Astronautical Engineering net: firstname.lastname@example.org
Department of Aeronautics & Astronautics fax: 513-476-7621
Air Force Institute of Technology
Wright-Patterson AFB, OH 45433-7765