AVELLA, Pa. -- A fluke rainstorm at an ancient rock shelter in western Pennsylvania has brought a renowned archaeologist back to the site of where a furious debate was launched in 1973 over when the first humans came to the Americas.
As a young archaeologist, Jim Adovasio found radiocarbon evidence that humans had visited the Meadowcroft site 16,000 years ago. To archaeologists it was a stunning discovery that contradicted the so-called Clovis first theory, which dated the first settlement in the Americas to New Mexico about 13,000 years ago.
The question is important because it ties into bigger questions on how and why so many different cultures developed in the Americas, and whether they all descended from one group that came across from Asia or arrived in multiple waves.
On that question, Adovasio's theory of multiple visits has mostly won out since other pre-Clovis sites have been discovered in North and South America.
The picture of early humans in the Americas "is so much more complicated than we ever thought it was 40 years ago," said Adovasio, a Mercyhurst University professor who returned to Meadowcroft after a decayed tree root let heavy rain flow into a part of the enclosed dig area in late July. The damage was unfortunate but presented an opportunity to re-examine the site, he said.
Meadowcroft is located on the banks of a small stream, about 7 miles upstream from the Ohio River. The overhanging sandstone ledges provided a perfect place for roving band of early humans to shelter from the elements.
"It has all the attractions of a prehistoric Holiday Inn, and that's why they used it," Adovasio said, noting that some early groups stayed for only a few days, but the spot was passed down through oral histories and people returned, eventually for longer periods.
The site was discovered when local historian Albert Miller found artifacts in a groundhog hole on family land in 1955, and he sought out professional archaeologists to investigate.
Dennis Jenkins, a leading archaeologist from the University of Oregon, agrees with Adovasio's broader points about the Clovis debate, but said some still have questions about Meadowcroft's exact age.
Jenkins said the main concerns are whether the earliest plant remains that helped date the Meadowcroft site are accurate, but he added that it looks like Adovasio "has done very meticulous work at Meadowcroft."
A recent poll of archaeologists found that opinions on Meadowcroft are still divided, with about 38 percent agreeing with Adovasio's dates, the same number unsure, and about 20 percent saying it isn't that old, according to a study published last year in the Society for American Archaeology.
Regardless, it is clear Meadowcroft has helped to change the way some younger archaeologists think. Instead of holding onto Clovis, they're open to multiple possibilities.
"I like archaeology because it keeps changing," said Anne Marjenin, the 28-year-old director of the Mercyhurst Archaeological Center lab, as she recorded details of the new Meadowcroft dig last week. "I don't think we should just dismiss any kind of evidence because there may not be a lot of it."
At Meadowcroft, archaeologists scrape away at layers of sand and dirt with razor blades, bagging each layer for separate laboratory analysis.
The current dig is examining the flood-damaged section in hopes of uncovering more details about the layers of the site that date from roughly 3,000 to 7,000 years ago, Adovasio said.
But the bigger message is that even as archaeologists learn more about Meadowcroft, other possibilities beckon.
Adovasio said there are other prehistoric sites near Meadowcroft, and he believes some of them have evidence of very early visits, too.
The Meadowcroft site is a National Historic landmark and is open to the public from Wednesday through Sunday during the summer. Visitors can watch the dig from a special observation platform built around the site.