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FIGURE 4 Meteor Crater, Arizona. [Photo courtesy of David Roddy and the
U.S. Geological Survey.]
meteorites. Gilbert reasoned that if impact created this circular
crater, the meteorite must have fallen vertically and could still be
buried directly beneath the crater, where its iron magnetism would
give it away. Surrounding the crater should be a mixture of ejected
rock and meteorite fragments that together would have a greater
volume than the now-vacated crater.
Announcing that he was "going to hunt a star," Gilbert and his
assistants set out in October 1891 to measure the expected magnet-
ism of the crater floor, but found none. The volume of ejecta turned
out (by coincidence, we now know) to just match the volume of the
crater. As a responsible scientist who followed where the evidence
led, Gilbert had to conclude that impact had not created the crater.
Such a conclusion was especially obligatory in this case, since Gil-
bert had set out his intended investigation of Coon Mountain as a
model of the scientific method. He published his findings in 1896,
four years after his hotel room experiments. 9 Having failed to find
the predicted evidence of impact, Gilbert was forced to conclude
that something other than impact, most likely a deep-seated gas
explosion, had created the crater. Thus developed one of the great
ironies in the history of geology: Gilbert correctly concluded that
impact created the lunar craters, but incorrectly concluded that it
had not created the most visible of all terrestrial craters. For four de-
cades, Gilbert's enormous prestige and apparently meticulous meth-
ods put the theory of impact craters to rest.
The crater attracted not only scientific but commercial interest.
Geologist and mining entrepreneur D. M. Barringer, "unaware that
such ideas were geological heresy," as Marvin puts it, 1 0 decided that
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