MEADOWCROFT, PENNSYLVANIA NOW READY FOR VISITORS

Meadowcroft rock shelter (Pennsylvania) is the oldest known site of human habitation in North America, at least 16,000 years old. Its 52 carbon dates, in almost perfect stratigraphic order, reflect a continuous human record for 16,000-plus years. "It was like a Paleo motel," guide Eleanor Crowe said. "People would come along Cross Creek, seven miles from the Ohio River, and stay here, from the earliest Paleo-Indians to the time of European settlement."

Closed in 2007, the landmark has reopened with a new shelter of its own, a $2.3 million enclosure that's bolted into the bedrock. A new roof protects the archaeological dig, and new platforms allow more visitors to see the excavated levels and start piecing the timeline together for themselves. "Until we completed the new structure, there was just a temporary wooden structure built by the archaeologists to protect the site," said director David Scofield.

Archaeologists began digging and sifting in 1973, led by University of Pittsburgh professor James M. Adovasio. He and his students held six consecutive field schools there. For now, the dig is quiet, but millions of bone fragments, plant materials and cultural artifacts such as basketry fragments are being studied at Mercyhurst.

Facing south for warmth, with a good east-west breeze, this site 50 feet above the north shore of Cross Creek would stay dry and well ventilated. It remained more than 93 miles south of the ice front. Springs to the east and west made it ideal for hunter-gatherers to stay for a few days or set up a fall hunting camp.

We can still see a deer rib bone sticking out of the rock, proving that Indians butchered their kill here about 400 years ago. But what of the first inhabitants? As Adovasio and his students bore down into the layers of silt, the cultural evidence gets older and older. By the time they hit bedrock 15 feet down, Adovasio was sending specimens for carbon dating, and the word back was staggering: at least 16,000 to 17,000 years old.

Some archaeologists claim Adovasio's samples were contaminated, possibly by nearby coalfields. After results came back from four labs around the world, with no signs of contamination and identical carbon dates, some scientists changed their minds. Most of the site's critical artifacts are at Mercyhurst, but travelers can see some projective points from 4,000 BCE to 2,000 BCE in the Meadowcroft Museum.