If we could see all the holes gouged in the Earth by asteroids, we'd run screaming for cover.
- By Tony Reichhardt
- Air & Space magazine, May 2004
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My next stops are Versailles (locally pronounced "ver-SALES") and Jeptha Knob, two other suspected impact structures in Kentucky. They lack shocked quartz or other proof and so are unconfirmed as craters but very likely are anyway.
There's nothing particularly asteroid-attracting about Kentucky. I could easily have chosen neighboring Tennessee or Missouri, each of which has two confirmed craters, or stayed home in Virginia and visited the Chesapeake Bay, which overlies a 35-million-year-old crater. At least 168 impact scars have been identified on Earth, with new ones added to the list each year, and hundreds more suspected. The confirmed ones range from the 200-mile-wide Vredefort crater in South Africa to a piddly little car-size dent in a field near Haviland, Kansas. We only know about that one because it happened so recently, about 1,000 years ago. Most craters smaller than 12 miles in diameter are long gone, eroded flat over geologic time, covered over with sediments, or subducted back into Earth's mantle.
The official list of confirmed craters, called the Earth Impact Database, is kept by geologists at the University of New Brunswick in Canada. Why them? In part because Canada, having large areas of old, exposed crust, has lots of old craters. And in part because Canadian scientists have taken an interest in the subject. Crater hunting is like that, says Richard Grieve, a geoscientist and impact expert with Canada's Natural Resources Department, which used to maintain the database. A dozen craters turned up recently in Scandinavia and Finland, he says, "quite simply because there's been a group of people who've made it their business to go out and find them."
Mark F. Thompson, a geologist and geospatial data analyst with the Kentucky Geological Survey, would like very much to add a new crater to The List. Actually, two craters: Versailles and Jeptha Knob. Today Thompson and I are driving in a soft rain through the rolling bluegrass country outside Lexington, past thoroughbred horse farms and bourbon distilleries, not far from the small town where Colonel Sanders opened his first chicken joint. I feel like I'm driving over a Howard Johnsons placemat showing the landmarks of Kentucky.
I never would have recognized the mile-wide Versailles structure had Thompson not pointed it out. For one thing, there's no obvious depression. The circular outline of the crater is marked only intermittently by small, deep sinkholes in the limestone terrain. The impact, if one occurred, happened as long as 440 million years ago. Versailles was discovered in 1962 and was originally thought to be a giant sinkhole itself. But later geologic mapping showed faults around the perimeter similar to those seen around impact craters. And the surrounding fields yielded a surprising number of breccias, lumpy conglomerate rocks made of sharp rock fragments fused together. Geologists often find breccias near volcanoes, but there aren't any volcanoes around here.
By the roadside, across a barbed-wire fence, Thompson spies what he thinks might be a breccia. "I wouldn't mind having a piece of that for myself," he says, then decides against it. We haven't gotten permission from the landowner, and he can get a piece when he comes back. He'll need to do more extensive fieldwork if he wants to prove Versailles a crater.
Kentucky's other candidate, Jeptha Knob, is 24 miles away. A three-mile-wide circular formation with a clump of hills sticking up from its center, it was one of the original "cryptovolcanic" structures that puzzled Walter Bucher back in the 1920s. Geologic maps reveal a neatly circular pattern of faults at the perimeter, where Thompson shows me contorted rock beds, evidence of the impact that occurred some 440 million years ago, back when Kentucky was under a warm, Caribbean-like sea. This was long before the dinosaurs, so there were no large animals to look up at the screaming fireball. Just a bunch of shelled creatures whose fossilized corpses I can easily pick out of the crumbly Ordovician-era breccia with my finger.
We head toward the center of the crater, which is on land owned by Cal Schmidt, a genial, soft-voiced man who looks to be in his early 70s. Schmidt greets us at his home on the edge of a small private lake. He's obviously proud of owning the central uplift feature of a suspected impact crater. When I tell him I spent the day before at Middlesboro, he quickly turns to Thompson and asks, "Is Middlesboro bigger than me?" A joke, but with a hint of concern.