Rosetta Stone - Four Revolutions in the Earth Sciences - page 162

Much of the nearby ejecta slumps back into the crater. The process produces an
explosion like that of a bomb, and it leaves a circular crater regardless of the met-
eorite's angle of impact, something that Gilbert and the other pioneers had no way
of knowing.
Shoemaker's detailed geological mapping showed that the rocks around Meteor
Crater perfectly manifest this theoretical process. The coup de grace to crypto-
volcanism was his discovery of two rare minerals derived from quartz at Meteor
Crater, one named coesite after its synthesizer. Scientists had produced the two
minerals in extreme high-pressure laboratory experiments, but they had never been
found in nature.
Bucher's Last Field Trip
In Walter Bucher's paper at the second of the two 1964 conferences, he argued
that three of the largest cryptovolcanic structures are associated with known geo-
logic structures and thus cannot have resulted from random events. 8 One of the
three “so-called meteorite scars” on which Bucher focused, the Wells Creek Bas-
in in Tennessee, he said was “aligned along an anticlinal axis.” Another, the Ries
structure in Germany, was related to “the crest of a major downfold.” The third,
the Vredefort Dome in South Africa, lay “in line with four other circular domes.”
This type of evidence may be suggestive, but it is hardly conclusive. Countless an-
ticlinal folds and downfolds exist, and a meteorite landing at random might well
hit near one of them.
Because some cryptovolcanic structures have shatter cones and coesite, yet ac-
cording to Bucher impact could not have caused the structures, he had to conclude
that the two putative markers must “not be accepted as sufficient evidence for im-
pact from above.” 9
On May 2, 1964, just before the conference convened, at Shoe maker's invit-
ation Bucher visited Meteor Crater. A former Bucher student, Wolfgang Elston,
was along to provide a first-person account. 10 “Gene's meticulous structural map-
ping convinced Bucher of the realities of the overturned rim and outward thrusts,”
Elston wrote, continuing, “as we left, [Bucher] conceded Meteor Crater, 'but the
Ries, that's different.'”
The “Ries” is a large circular geologic structure in Germany long believed by
Bucher and German geologists to be of volcanic origin. 11 In July 1960, just after
the death of his father, Shoemaker, his wife Carolyn, and his mother were on their
way to Copenhagen, where Gene would attend a conference. Deciding to do some
“geological sightseeing” on the way, the family stopped by the town of Nördlin-