He's still puzzling out some of the complex evidence himself, trying to reconstruct the details of the impact, which partly depend on what the impactor was made of (there's a big difference between the wallop of a loose iceball and that of a chunk of rock or iron), and how big it might have been (100 to 500 yards across, he guesses). He's starting to think the crater might not be as neatly circular as it appears, that it may be more elongated.
The Middlesboro impact was big enough to form what's called a complex crater. The initial excavation was followed by a rebound of material from the center, creating a central uplift feature, the way a pebble dropped in water splashes up a jet of water. Fractured material then slumped back into the crater, and the outer rim became terraced, unlike the neat bowl you find at the smaller (and fresher) Meteor Crater.
In this case the central uplift feature-ground zero-is on the grounds of the Middlesboro Golf Course, which dates back to 1889 and bills itself as the oldest golf club in the country. On this unseasonably warm Tuesday afternoon in November, the course is mostly empty. I watch a twosome approach the second green, right behind me. A guy who looks like he just stepped from the Land's End catalog whacks stiffly at a golf ball, which rolls about 10 feet. His next shot dribbles onto the green, and two undistinguished putts later, he picks up his ball, fuming. He looks to be having a bad day.
Of course, bad days are relative. Right next to the first tee (a 273-yard par 4) is an old, weathered block of sandstone that shouldn't be there. By rights this particular rock should be buried 1,300 feet below, with the rest of the Lee Sandstone formation. The asteroid that hit some 300 million years ago yanked it up in a horrifying instant, the central peak uplifted from underneath the now empty bowl.
Out at the perimeter of the original crater, Milam shows me rock beds turned completely upside down, a disorder that can't easily be explained by trivial events like earthquakes. "When I bring professional geologists here who aren't familiar with impacts, they just scratch their heads," he says. In the normal course of geological research, they would never encounter forces like the ones on display here.
Driving north from Middlesboro on Highway 25 late that afternoon, I see that the exposed rock on either side of the road returns to its normal pattern. Stacks of beds, the once-muddy floors of ancient seas, are as flat and regular as the layers of a cake. Order is restored. Leaving this place of past violence, I see a hand-drawn sign off the highway that says "Prepare to Meet God."
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.