Land Lines
10:12 am
Thu October 13, 2011

Land Lines - Meteor Crater


MPC: There are times when geology really hits home. Fifty-thousand years ago, an asteroid streaked toward the Colorado Plateau, searing a white hot line across the skies of Northern Arizona. It slammed into Earth at 26,000 miles an hour. Rocks were vaporized and any nearby animal--mastodon, camel, or ground sloth--was instantly killed. The impact whipped up winds of a thousand miles an hour.

REH: The house-sized asteroid ripped open a giant hole now known as Meteor Crater. A hundred years ago, locals called this place Coon Mountain. From a distance the upturned rim looks like just another butte out on the flat windy desert west of Winslow. But up close, its size is astounding--560 feet deep, 4,000 feet across. Strewn around the crater were dark chunks of iron and nickel--the ADiablo irons. It was word of those Airons that attracted Daniel Moreau Barringer.

The Philadelphia mining engineer was interested in mineral potential, and in 1905 he published a paper asserting the crater was the result of an impact. Barringer went up against august scientists of the day in a controversy about what actually created the crater. Grove Karl Gilbert, head of the U.S. Geological Survey, had already applied the best science of the nineteenth century and concluded the crater was the result of a volcanic steam explosion. Still, Barringer put his money on a meteorite--literally. He bought the crater and the land surrounding it, drilled into the floor, and hoped for the best. But the scientific community was not swayed and Gilbert's volcanic theory persisted.

MPC: Half a century later in the 1960s, geologist Gene Shoemaker revisited the origin of the crater. He looked at the intense cluster of meteorites that had intrigued Barringer. Under a microscope, Shoemaker examined pieces of native rock that had been ejected onto the surrounding plain. In nanoseconds, quartz of the Coconino Sandstone had been shocked into a new crystalline structure that could only occur with an instantaneous impact. The force had splashed a wave of rock up and out in all directions. Shoemaker mapped fracture patterns caused by the impact and saw that the natural order of strata on the rim had been reversed. The overturned layers--along with the shattered and melted rock--were undeniable signatures of a spectacular blast. Working at the height of the Cold War, Shoemaker and other scientists likened this to a nuclear explosion equal to twenty million tons of TNT.

REH: Daniel Barringer, the determined miner, spent the rest of his life looking for iron and nickel at Meteor Crater. His exploratory drill rigs are still visible at the bottom. Though he never struck pay dirt, his real reward came later when his theories were finally accepted.

It's now gospel that Meteor Crater is a scar left by an asteroid the first proven and best preserved impact feature on Earth. In the distant past, one may have caused the extinction of the dinosaurs. Will another asteroid hit earth again B most likely, yes. On average, a large meteorite strikes our planet about once every two thousand years. But you don't need to lose a lot of sleep over it. The chances of another one hitting right here are vanishingly small.

I'm Rose Houk. And I'm Michael Collier for Arizona Public Radio.