Predictions

Officer followed up his 1992 paper (with Drake and Meyerhoff) with one in the journal Geology (with Dartmouth colleague J. B. Lyons and Meyerhoff) and, later, with a section in his book with Page, The Great Dinosaur Extinction Controversy."" In the book, after setting up the anti-impact position by citing the various (to him at least, successful) challenges to the Alvarez theory that Charles Officer has championed through the years, the two authors come at last to the vexing issue of the crater itself. But for them, Chicxulub is not vexing at all; they merely rebury it: "The impactors [pro-impact scientists] would have something of a case if they would point to a massive impact crater . . . dating to the proper time in the geological record. They have searched far and wide around the world for evidence of even one such crater, but sadly for them, they have come up wanting. . . . One of the things that did not happen at the K-T boundary was impact by a gigantic meteorite."42

How, in the face of all the evidence just reviewed, can two authors come to such an opposite conclusion from almost everyone else who has studied the Chicxulub crater? Here is how Officer and Page managed it:

• Their book appeared in July 1996, allowing plenty of time for them to incorporate the results of the new drilling tests that by 1994 had begun to be reported at scientific meetings and in abstracts. Yet Officer and Page base their conclusions on only two sources: a report from 1975 and Meyerhoff's three-decades-old notes.

• They do not mention the strikingly concentric gravity patterns, the cenotes, or the import of the size of the structure (at 170 km to 300 km, perhaps the largest on the earth).

• The older paleontologic interpretations dated the Chicxulub structure at 80 million to 90 million years, far older than K-T time. Officer and Page mention the modern radiometric age measurements, but say only that they "give values ranging from

58.2 to 65.6 million years...in accord with what would be expected from samples...with loss of argon content."43 They compare this with the revision of Manson's age (although there the more recent measurement gave an older, not a younger age). To the unwary, their discussion leaves the distinct impression that the most recently obtained ages at Chicxulub are suspect and that the original ones stand unchallenged. Officer and Page do not reveal that two different laboratories conducted the modern age measurements on the Chicxulub igneous rock, that they used the highly precise argon-argon method, and that both gave precisely the same result—exactly 65.0 million years. It is true that in one of the studies, a few of the samples gave ages as low as 58.2 million years, which the original authors attributed to alteration, but most from that study gave 65.0 million years. Since argon loss causes ages to be younger than they really are, not older, the older ages are the more reliable. As testimony, in the other of the two dating studies, three samples of the Chicxulub melt rock gave 64.94, 65.00, and 64.97 million years.

• Although they list among their references the paper by Dartmouth scientists Blum and Chamberlain, who used isotopic ratios to establish a genetic link between the Chicxulub melt rock and the Haitian tektites, Officer and Page never actually mention this result in their text.

• They do not reveal that the Chicxulub igneous rock has anomalously high iridium levels. They acknowledge that it does contain shocked minerals, but pass them off as "of the volcanic/ tectonic type."44 (The original authors, however, clearly stated that the shocked minerals show the multiple deformation planes indicative of impact, features that have never been found in volcanic rocks.45) They do not mention that the Chicxulub melt rock is reversely magnetized, consistent with (but not proof of) a K-T age.

• Although in an earlier section they discuss the visit of the sedimentologists to Mimbral, in their section on the crater search they never mention the conclusion that the sedimentologists reached: that the Mimbral sediments "were deposited on short time scales (more likely 100,000 seconds than 100,000 years)."46

Chicxulub has met each of a reasonable set of predictions for the impact crater, and then some. First, the concentric gravity patterns and its huge size show that Chicxulub is not a volcanic feature but an impact crater. Second, with its breccias and a melt rock that is reversely magnetized and enriched in iridium and shocked minerals, it has the features expected of the K-T crater. Third, Chicxulub formed at precisely the time of the K-T boundary. Fourth, its age and isotopic geochemistry link it conclusively to the unusual Haitian tektites. Finally, turbidite-like K-T deposits enriched in iridium, spherules, and spinels, and believed by most experts to have been laid down in a day or so, encircle Chicxulub. In sum, if this structure is not the K-T crater, it is hard to imagine what would ever qualify. One could describe this result using the tiresome metaphor of "smoking gun," but in this case it is not really apt. When the perpetrator is long gone, merely finding a smoking gun is not enough— you need to know whose fingerprints are on it.

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