To Hunt a Star - Four Revolutions in the Earth Sciences - page 149

One reason that the earliest students of the Moon did not conceive of meteorite im-
pact as a realistic hypothesis is that they could not imagine what might have fallen
to create the lunar craters. But after the descent of thousands of meteorites on a
French village in 1803 and the almost simultaneous discovery of the asteroids, im-
pact became at least a theoretical possibility.
By far the most distinguished scientist to attribute lunar craters to meteorite im-
pact was Grove Karl Gilbert (1843-1918), the chief geologist of the United States
Geological Survey. One biographer, drawing on the phrase that Gilbert himself
used to describe the USGS, subtitled his topic “A Great Engine of Research.” 4
In 1968 a group of geologists that included Gene Shoemaker reenacted Major J.
W. Powell's famous 1869 voyage down the Colorado River through the Grand
Canyon. Sitting around their campfire one night, they fell to debating who had
been America's greatest geologist. They chose Gilbert. 5 When he died, another
greatgeologist,WilliamMorrisDavis,wroteGilbert'sbiographicalmemoirforthe
National Academy of Sciences. 6 It was 323 pages long. Davis's own memorialist
noted his subject's affectionate devotion to Gilbert and ranked Davis's biographic-
al memoir “as one of the finest analyses of method and mental process in scientific
literature, a work truly worthy of its subject.” 7
Gilbert's interest in impact craters may have begun in 1891, at a meeting of
the American Association for the Advancement of Science in Washington, D.C.,
where he heard the mineralogist Arthur E. Foote describe a “circular elevation
. . . occupied by a cavity nearly three-quarters of a mile in diameter” close to a
small trading post in northern Arizona named Canyon Diablo. 8 Foote told how,
scattered on the surface around the cavity, were unmistakable iron meteorites, one
of which contained diamonds. Foote noted that the meteorite fragments “would al-
low a good deal of self-deception in a man who wanted to sell a mine.” 9 Revealing
a wry sense of humor that comes in handy for the field geologist, Foote said that
he would have brought back photographs of the specimens, but “a severe gallop
across the plain had put my photographic apparatus out of order” (414). He noted
that “a careful search failed to reveal any lava, obsidian, or volcanic products.”
Most audience members may have perked up at the mention of the diamonds,
but the scholarly Gilbert was more interested in the origin of the “so-called crater,”
which he said “was like the depressions on the surface of the Moon produced by
impact of an enormous meteoritic mass.” 10
Gilbert determined to go to Arizona and see for himself, writing a friend of his
“peculiar errand to hunt a star” and adding: “Numerous fragments of meteoric iron
have been found in a tract adjacent to a 'crater,' and the crater differs from others
in that it is composed of sandstone and limestone and has no volcanic rock.” This