Meadowcroft Rockshelter is an inviting sandstone overhang in a tributary valley of the Ohio River that's been welcoming anglers, hunters and travelers since the Paleo-Indians. The site in Avella, 30 miles southwest of Pittsburgh (Pennsylvania, USA), is now a National Historic Landmark. 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 and raked at an improbable 17-degree angle. 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.
     Archaeologists began digging and sifting in 1973, led by James M. Adovasio, a University of Pittsburgh professor. Later, Adovasio founded the Mercyhurst Archaeological Institute. 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.
     As Adovasio and his students bore down into the layers of silt, the cultural evidence kept getting older and older. By the time they hit bedrock about 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. But perceived wisdom in archaeology said that people arrived in the New World relatively late, about 11,500 years ago. Could Meadowcroft really be 4,000 years older? Adovasio and his work set off a firestorm that has raged for more than 30 years. Some archaeologists claim his 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 those critical artifacts are at Mercyhurst, but travelers can see some items from 4,000 BCE to 2,000 BCE in the Meadowcroft Museum. About a third of the site remains untouched, preserved for future archaeologists with as-yet-undreamed technologies.

Source: Miami Herald (31 May 2009)