FRESNO — Remains of what scientists believe could be the oldest structure ever found in North America have been dated by means of radiocarbon to at least 9,750 years, an archeologist said Saturday.
The dating was made possible by the discovery of charcoal from a hearth found in the clay-floor of what was once a 12-foot-long oval-shaped residential building near Bear Valley in the Sierra Nevada about 150 miles east of San Francisco.
"We are tremendously excited because this is the oldest structure apparently ever found in North America," said Melinda Peak, of Peak and Associates Inc. of Sacramento.
"It pushes back our knowledge about man and particularly his use of the mountains," she added. Peak's mother, Ann, is chief archeologist for the family company which in August found the structural remains eight feet underground while excavating the site of a hydroelectric project along a tributary of the Stanislaus River in Alpine County.
Because of its antiquity, as well as the firm's discovery earlier in the year of 12,000-year-old spear points at a prehistoric campsite 30 miles away, scientists expect some of early man's history on the continent to be revised.
"This in the very least will cause archeologists to dig deeper, because in the past many believed man had not even been in North America that long ago," said Walt Woolfenden, an archeologist for the National Park Service.
A discovery at Hell's Gap, Wyo., was previously believed to be the oldest man-made structure on the continent, dated at 8,000 years, said Peak.
The Sierra Nevada site has attracted nationwide attention since news reports of its discovery. At the time, Ann Peak estimated it was 10,000 years old. Carbon-dating, which measures the decay of carbon-14, has revealed the age with a margin of error of 180 years either way, she said.
The new find is expected to fuel a debate about how long ago humans migrated to North America. Sites and structures tentatively dated up to 32,000 years ago have been found in South America, but many scientists speculate those early inhabitants may have come by boat across the ocean since few sites more than 6,000 years old have been found in North America.
Scientists are sharply divided over when migration to the Americas occurred. Some say humans arrived 20,000 to 35,000 years ago, while others contend migration began no more than 13,000 years ago.