How Discoveries at Meadowcroft Rock Shelter Changed the Date of the First Human Migration to North America
by Tom Imerito
Five decades ago beneath a rock overhang in Washington County, Pennsylvania the Atomic age collided with the Stone Age. Since then, Meadowcroft Rock Shelter has been a focal point of archeological innovation and discovery as well as scientific controversy and iconoclasm.
The story begins on Nov 12, 1955, when a gentleman farmer and amateur archeologist named Albert Miller noticed some burnt bone and flint flakes among the dirt that a woodchuck had excavated while burrowing in the forest floor beneath a rock overhang on his farm. His interest being piqued, Miller began digging. At a depth of thirty inches he discovered a flint knife, which he recognized as an important archeological find. Fearful of looting, he kept the site a secret for the next fifteen years while he sought professional archeological help.
The task fell to a young University of Pittsburgh archeologist named James Adovasio, who in 1973 took stewardship of the site primarily for its promise as a field training facility for budding university archeologists. Beginning that summer, the Meadowcroft diggers began to excavate, sort, map and catalog the site’s hundreds of discrete layers. Eventually more than two million prehistoric specimens, including human-made artifacts, plant residues, ash, charcoal and animal remains would be unearthed.
Then, on July 13, 1974, upon receiving the results of the site’s first radio carbon dating tests Professor Adovasio found himself catapulted into the center of a controversy that would call into question archeology’s tenaciously held date of initial human migration to North America of 13,500 years before the present. The date had been established by the 1929 discovery of a fluted spearhead in Clovis, New Mexico and subsequent finds of similar points across North America. But the Meadowcroft radiocarbon date came in at 16,000 years.
Although Meadowcroft was the most technologically advanced archeological dig in the world at the time and its methodologies were impeccable, carbon dates were initially dismissed simply because no other similar sites had been found up to that time. In retrospect, the reasoning appears to have been ironic because scientific discoveries, by definition, have no similar counterpart, that’s why they’re called discoveries.
In testament to the value of perseverance, Dr. Adovasio stuck to the scientific evidence and continued to excavate, despite widespread disagreement about the carbon dates. The site was covered to protect the excavation from the ravages of weather, animals, and forest debris; electrified with a tunable lighting system and power for tools; a telephone line and modem permitted instantaneous communication between the site and the University of Pittsburgh’s mainframe computer, at a time when the term broadband had not yet been coined; and cadres of multidisciplinary collaborators, including University of Pittsburgh geologists, sedimentologists, paleontologists, paleobotanists and climatologists joined in.
Then in 1999, a contingent of world renowned archeologists countenanced a remarkably well preserved site at Monte Verde, Chile with agreement that it had indeed been inhabited before 13,500 years ago, thereby breaking the Clovis First barrier which had stood for half a century. Subsequently, a similar group confirmed Meadowcroft’s claim of 16,000 years of continuous human habitation. To date more than a dozen sites indicative of human habitation before 13,500 years ago have been discovered throughout North and South America.
Today, Meadowcroft Rock Shelter is a living archeological museum protected by a magnificently designed building that serves to: curate the existing excavation; cover future excavations; and provide a place for visitors to look back at a few vestiges of humankind’s first activities on the North American continent. As it stands now, the eastern portion of the Rock Shelter remains under the roof, but undisturbed, awaiting the advance of new scientific tools for excavation and analysis. “When you excavate an archeological site, essentially you destroy it,” Adovasio said in an interview. “So we want to preserve what we have for future generations to explore.”
I guess we’ll just have to wait for the future to have a better look at our past.
This story first appeared in Tom Imerito’s TEQ column, Science Fare.
©Copyright 2007 Thomas P. Imerito/ dba Science Communications