CCNet 98/2003 - 6 November 2003
K/T MASS EXTINCTION DEBATE WIDE OPEN AND IN FULL SWING
It is nice to read such interesting and open debates! This is the way
Science should work! All participants can present their arguments
(flawed arguments are quickly dismissed by opponents), and a scientific
audience can compare the logic and weight of arguments of both sides.
K/T MASS EXTINCTION DEBATE WIDE OPEN AND IN FULL SWING
The Geological Society, November 2003
Welcome to the Chicxulub discussion page
This page contains discussion related to Keller, Adatte & Stinnesbeck's article, The Non-Smoking Gun (http://www.geolsoc.org.uk/template.cfm?name=NSG2349857238495). The most recent items in the discussion are to the top of the page. If you wish to contribute to this moderated on-line discussion, please Email the Site Editor (firstname.lastname@example.org)
13th impact crater associated with K/T boundary
From Tom Van Flandern* Received 5.11.03
Last year, a British team of scientists announced the discovery of a multi-ringed crater (named Silverpit) with a central peak beneath the floor of the North Sea, believed to have been caused by an asteroid impact between 60 million and 65 million years ago [1-4]. The crater has 10 concentric rings from 2-20 km in diameter. The rough dating suggests that the asteroid that caused Silverpit might have been a chunk that broke off the larger asteroid that hit the Yucatan Peninsula 65 million years ago. Together with the Chicxulub and other craters, this discovery gives new support to the idea that killer objects from outer space may have sometimes arrived in pairs or even swarms. "It's so clear," said Dr. Gerta Keller, a geologist and paleontologist at Princeton, who studies the links between cosmic bombardments and life upheavals. "A tremendous amount of new data has been accumulated over the past few years that points in the direction of multiple impacts."
Actually, that brings the list of impact craters sometimes associated with the K/T boundary (65Ma) to 13. These are: Beyenchime-Salaatin (Siberia), Eagle Butte (Oregon), Upheaval Dome (Utah), Manson (Iowa), Kara (Western Siberia), Kamensk (Siberia), Gusev (W. Russia near Ukraine), Unnamed (Pacific Ocean), Chicxulub (Yucatan), Belize (south of Yucatan), Haiti (Caribbean), Alvaro Obregón (N. Mexico), Silverpit (North Sea) [5-10]. However, the global distribution of these impacts argues strongly against chunks off a parent asteroid, which would be expected to have much less than a hemispheric distribution, assuming Earth's atmosphere is the agent responsible for the break up. Capture and tidal break up by Earth, similar to Jupiter's capture of Comet Shoemaker-Levy 9, is extremely unlikely (by a factor of over 10 million) because Earth has a much smaller mass and is closer to the Sun. The clear implication of this global terrestrial cratering cluster is the explosion of a planet-sized parent body in the main asteroid belt, a hypothesis for which considerable astronomical evidence already exists [11-22].
(2002), Nature 418, 520-523.
(1996), "Terrestrial impact crater list", http://www.meteorite.ch/crater.htm
(1991), Lunar&PlanetarySci. XXII, abstracts, 961-962.
(1993), Nature 363, 670-671.
(1993), Nature 363, 615-617.
(1980), Nature 288, 651-656.
(1998/03/12), "More evidence points to impact as dinosaur killer", JPL Press Release 98-42, NASA HQ & Pasadena, CA.
T. Van Flandern, Dark Matter, Missing Planets and New Comets, North Atlantic Books, Berkeley, chapter 11, (1993; 2nd edition 1999) - synthesis of exploded planet hypothesis (EPH) evidence.
Icarus 36, 51-74 (1978) - technical justification for the EPH.
http://metaresearch.org. "Solar System" tab, "EPH" sub-tab - recent updating and distilling of the most telling EPH evidence, and how its predictions have fared; to be published in 2002.
Mercury 11, 189-193 (1982) - the EPH as an alternative to the Oort cloud for the origin of comets.
Icarus 47, 480-486 (1981) - the EPH's "satellite model" for comets as an alternative to the "dirty snowball" model.
Science 203, 903-905 (1979) - asteroid satellite evidence, confirming an EPH prediction.
Science 211, 297-298 (1981) - technical comment on previous paper.
Asteroids, T. Gehrels, ed., U. of Ariz. Press, Tucson, 443-465 (1979) - theory and observations of asteroid satellites.
Dynamics of the Solar System, R.L. Duncombe, ed., Reidel, Dordrecht, 257-262 (1979) - short summary of selected EPH evidence.
Dynamics of Planets and Satellites and Theories of their Motion, V. Szebehely, ed., Reidel, Dordrecht, 89-99 (1978) -- short summary of selected EPH evidence.
Comets, Asteroids, Meteorites, A.H. Delsemme, ed., U. of Toledo, 475-481 (1977) - short summary of EPH evidence with technical critiques and author responses.
Science Digest 90, 78-82 + 94-95 (1982) - popular exposition of the EPH and its implications.
Multiple impacts not unusual
from Andrew Glikson* Received 5.11.03
Sir, The Archaean imapct records includes the following documented multiple impacts:
At least 2 and possibly more 3.47Ga impacts in the Antractic Chert Member, Warrawoona Group, Pilbara (Glikson et al., in press) and probably a double 3.47Ga impact in the Hoogenoeg Group, Barberton, South Africa (Lowe et al., 2003).
A double impact in the 3.24 Ga Mapepe Formation, Barberton, South Africa (S2 and S3) (Lowe et al., 2003).
A double impact in the 2.56Ga Bee Gorge Member of the Wittenoom Formation, Hamersley Basin (SMB-1, SMB-2).
A double impact in the 2.47-2.50Ga Dales Gorge Group, Brockman Iron Formation, Hamersley Basin, Western Australia (DG4 and DG7).
Major impact clusters are recorded in the late Devonian (Woodleigh, Siljan, Alamo Breccia, Charlevoix), late Jurassic (Gosses Bluff, Morokweng, Mjolnir), Late Eocene (Popigai, Chesapeake Bay). So far as the K-T boundary is concerned, already two impact structures are known (Chicxulub, Boltysh), as well as the fallout units recorded by Keller. The evidence suggests that double impacts and impact clusters are commonly recorded in the terrestrial impact record.
*Research School of Earth Science, Australian National University Canberra, ACT 0200
Smoking gun proponents "must defend themselves"
From Andrei Ol'khovatov, PhD Received 5.11.03
Sir, It is nice to read such interesting and open debates! This is the way Science should work! All participants can present their arguments (flawed arguments are quickly dismissed by opponents), and a scientific audience can compare the logic and weight of arguments of both sides.
My impressions, which are those of a person who is interested in Chicxulub but was never deeply involved in this research, are as follows. It seems that on the basis of "proved science", the arguments of G. Keller sound more logical, so her opponents have to defend themselves. It seems that their best argument is that our understanding of the processes discussed is not good enough for any solid conclusion to be drawn. This argument is hard to overcome, as indeed, here we are in terra incognita. For example, our understanding of all large impact phenomena is based on our knowledge of relatively small meteorite impacts extrapolated (with help of numerous calculations) to impacts many orders of magnitude larger.
Numerical calculations depend on a physical model of the event under consideration. In the case of smaller events, results could be verified just by comparing the outcome of one's calculations with reality. It is very much more complicated in the case of large impacts. So, all models of large impacts are "unverified" at the moment.
To sum up. It seems that nowadays a "complete victory" is not possible due to "being in the field of unknown". My impression is that more research should be conducted. And currently we should to recognise (at least to ourselves) that we really don't know why dinos disappeared!
*Moscow, Russia www.geocities.com/olkhov
The timing's right
From Michael Paine* Received 4.11.03
Sir, The debate over the timimg of the Chicxulub impact is fascinating and indicates a healthy state of scientific research on this topic. Irrespective of the timimg of the event, however, the wide range of research that has been conducted since Chicxulub's discovery has shown that the average frequency of such impacts is around 50 to 100 million years and the multiple environmental consequences of impacts the size of Chicxulub can easily account for the observed mass extinctions. In other words, the Chicxulub impact is an entirely plausible explanation for the KT extinction event.
Maybe there were multiple impacts and traces of the others have been lost to subduction and erosion or maybe there are other causes. My money is still on Chicxulub (this has nothing to do with it being Melbourne Cup horse race day in Australia).
For more on environmental effects of impacts see
*The Planetary Society Australian Volunteers
More pluribus than unum
From Matt Terry*. Received Sunday 2 November
Sir, This vision of multiple large impacts fits better with the palaeontological protests that the dinos' decline was more stretched out than that postulated by a single global "Cosmic Winter" disaster. As Clube and Napier have made clear, the injection of one or more giant, likely cosmogenic, comets into the inner solar system necessarily implies its subsequent fragmentation into a swarm of hazards, as the Kreutz group gives current evidence for.
Three hundred thousand years is not so long a time, on deep-space timescales, and it is positable that the Chicxulub crater is one among many impactors from that time, again, in resonance with the slow decline of the Triassic hyper-fauna. Statistically, given the limits of our search and the oceanic plenitude, we should expect that Chicxulub is certainly not the only, or even the largest, impactor of its time.
*Tampa, FL, USA
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