Introduction

The Barringer Meteor Crater is located in North-East Arizona, to the East of Flagstaff (see map), set in sandstone desert. Boasting a diameter of approximately 1500m, and almost 170m deep, this is almost the largest impact crater in the world, second to a vast depression recently analysed on the Mexican Yucatan peninsula. Originally, the surrounding plain was speckled with over 30 tons of meteorite iron, scattered up to 8 kilometers from the crater itself. The towering crater rim is itself 45m higher than the bordering desert, and consists largely of giant smashed boulders, some as big as houses.

What Happened?

In 1891, the chief geologist for the U.S. Geological Survey, Grove Karl Gilbert, tested two opposing theories on the crater's existance; a giant meteorite impact, or the explosion of superheated steam caused by volcanic activity. If it were an iron meteorite that had created the crater, Gilbert reasoned that the meteor in question wold be a similar size to the crater, and furthermore the meteorite must then be taking up a substantial area within the crater. The volume of the hollow must then be less than the volume of ejected material in the crater rim. Magnets and compasses would also be influenced by the large mass of buried iron that should be present. Neither prediction was confirmed, and so Gilbert concluded that, being the only surviving theory, the crater must be volcanic. He stayed with this idea, despite the fact that there had never been record of volcanic rocks found in the area. The surrounding iron meteorite fragments were labeled as a 'coincidence'.

In 1902 Daniel Moreau Barringer, whose name the crater now bears, heard of the crater and, being a mining engineer, was somewhat interested. Upon learning small balls of meteoritic iron were randomly mixed with ejected rocks in the crater rim, Barringer decided this was a meteor impact crater. His reasonings, that he presented twice to the Philadelphia Academy of Natural Science, were in direct contrast to the conclusions previously drawn by Gilbert. Deciding on the practical approach, he set out to gather evidence in his support. His presented evidence was as follows: A. Millions of tons of finely pulverized silica present in the crater, only able to be created by enormous pressure. B. Large quantities of meteoritic iron scattered around the rim and surrounding plain. C. The random mixture of meteoritic material and ejected rocks. D. Different types of rocks appeared to have been deposited in the opposite to their natural order. E. No naturally occurring volcanic rock in the crater vicinity.

In 1928, after many unsuccessful attempts at mining the crater for metal, $200,000 was raised for a final mining assault on the meteorite. Barringer's directors, however, were very skeptical regarding success, and when the new mine shaft hit great quantities of water that could not be pumped out, they looked for a second opinion. They consulted senior astronomer F. R. Moulton, who first calculated the amount of energy produced by the impact of a meteor of sufficient size to create such a crater. He concluded that such a meteor would weigh only 300,000 tons - 3% of Barringer's estimte, and too small to justify further drilling. What's more, Moulton advised that such an impact would likely result in the absolute vaporisation of the meteorite. Work was halted at the crater the next year. Only weeks later, Barringer died of a heart attack.

Today's Opinions

It is widely believed by scientists today that the crater is approximately 50,000 old, and the meteor largely consisted of nickel-iron, suggesting it may have originated in the interior of a small planet. Approximately 50m across, it weighed roughly 300,000 tons, traveling at a speed of 64,000 kilometers per hour. The impact would have produced a 20-megaton force, equal to the detonation of 20 million tons of TNT.
Geologist Eugene Shoemaker published his landmark paper in 1963, analyzing the similarities between craters produced by Nevada nuclear weapons tests and the Barringer crater. Mapping carefully the layer sequences of underlying rock, and ejecta blanket layers where those rocks were deposited in reverse order, it was demonstrated that the Barringer crater and those caused by weapons detonations were nearly identical in all respects. With the publishing of this paper and it's convincing proof, Shoemaker succeeded in silencing the last few doubters.