The start of the 1960s solved one of the great mysteries of the American landscape east of Flagstaff, Arizona – a 50,000 year-old circular gash in the earth 560 feet deep and about a mile wide known by various names: Canyon Diablo crater, Barringer Crater or, most commonly, “Meteor Crater.” Westbound Americans after the Civil War and railroads expanding across the Southwest brought the crater to the attention of scientists who began in the 1890s to investigate the crater and look for its possible cause. Two conflicting explanations emerged at the end by the nineteenth century, one attributing the crater to a meteor of nickel-iron composition; the other (including the researches of the chief geologist for the UGS, Grove Gilbert) concluding it to be caused by the venting steam of a violent ancient volcano, in part, for the lack of an extant meteor at the site or magnetic traces of impact.
Daniel M. Barringer, 1860-1929
In 1903, Philadelphia mining engineer and businessman Daniel M. Barringer entered the controversy by staking a claim to the square mile around the crater. Barringer took the large iron fragments on and around the crater rim as proof for the meteor theory. He formed the Standard Iron Company to monetize iron deposits within the crater, and locate the iron’s source – the body of the meteor he thought must lay below the surface of the crater which no one, to that time, had been able to find. By 1906, researchers at Standard Iron in association with outside experts asserted and published their support for an impact meteor being the cause of the crater in Arizona. For over 25 years, until his death in 1929, Barringer plumbed the crater floor to a depth of 1400 feet searching for what he thought was a buried projectile from space, but to no avail.
What Barringer couldn’t know was that there was no meteor to find because it had vaporized on impact. In 1960 the geologist and planetary scientist, Eugene Shoemaker, supplied the hard scientific proof for Barringer’s and others’s assertions about a meteor. From his study of craters left by atomic bomb tests at Yucca Flats in the Nevada desert, Shoemaker discovered residues in the Arizona crater of specific substances – stishovite and coesite – that are formed only when quartz rocks are severely shocked by overwhelming pressure – naturally by some kind of impact event or artificially through a nuclear explosion. Thus were launched the fields of impact cratering and astrogeology which, before the 1960s, were in their infancies.
Eugene M. Shoemaker, 1928-97
After the work of Shoemaker and the birth of the idea of shock-metamorphic features, the search for craters on earth took off, and by 1970 researchers had tentatively identified some 50 so-called “impact structures” in various parts of the world, as well as reinvigorated the charting of impact craters on the moon, Mercury, and Mars through NASA and through organizations such as the Impact Field Studies Group. Since 1964 the site has served as a training spot for astronauts under the auspices of the USGS and NASA.
Probably the most-studied crater on earth, the work of the 1960s has advanced to include a calculation in 2005 of the speed of the asteroid into the crater at 27,000 mph, and computer simulations have estimated a required 300,000-ton mass to make the crater that came to earth 50,000 years ago – for an energy equivalent of a 10-megaton blast [Gerald G. Schaber, “A Chronology of Activities from Conception through the End of Project Apollo (1960–1973)”, 2005, U.S. Geological Survey Open-File Report 2005-1190. (PDF)]
Interestingly, Barringer and Shoemaker both went to Princeton University, though at different times.
Little did they know that the 1960s would bring their names together on sort of a joint project in Arizona; and history remembers both men. Shoemaker broke the meteor mystery east of Flagstaff in the 1960 working on a doctoral dissertation. For his part, Barringer has a crater on the far side of the moon named in his honor. In November 1967, the Department of the Interior designated the Meteor Crater a National Natural Landmark, and the Barringer family continues to administer the site as one of the most frequented destinations in the Southwest. For recent reminiscences by Mrs. Shoemaker, see https://science.howstuffworks.com/eugene-shoemaker-buried-on-moon.htm