And the seaweed picked up at the Monte Verde site provide a direct link to people living in the area today, some of whom also use some of the seaweed species medicinally.

"What we have found ... are nine species of seaweed that are coming from rocky and sandy beaches located about 55 kilometers (35 miles) west of the site," said archeologist Tom Dillehay of Vanderbilt University in Nashville, Tennessee, who led the study.

"It indicates to us that the people of Monte Verde had a much stronger coastal industry than we thought previously. It indicates to us that we might be talking about people who initially entered into the Monte Verde site from the Pacific coastline itself," he told reporters in a telephone briefing.

The Monte Verde site 500 miles (800 km) south of Santiago has long been controversial. Discovered in 1977, its contents have been carbon-dated to more than 12,000 years ago -- dates that careful calibration using tree rings and other information suggest are actually more than 14,000 years old.

CONTRADICTING CONVENTIONAL WISDOM

This clashes with the one-time conventional wisdom that humans first crossed from Siberia using a land bridge over the Bering Strait about 13,000 years ago and then spread over the American continents.

But it supports newer genetic, linguistic and physical evidence that suggest this migration took place earlier, at least 16,000 years ago.

And it shows the upper layer of the site was occupied more than 1,000 years earlier than any other reliably dated human settlements in the Americas.

Dillehay believes it supports his theory that early Americans moved slowly down the Pacific coast, learning about the local flora, fauna and other resources as they explored. They would have moved inland a bit as they encountered raging, turbulent rivers full of glacial snowmelt.

Older theories have focused on a human blitzkrieg, in which fast-moving groups spread over the continent quickly as they tracked and wiped out herds of big game.

Some of the seaweed had been pressed into cakes and chewed as quids, like tobacco is sometimes today. Others had clearly been cooked, Dillehay and colleagues said.

"All nine seaweed species recovered at Monte Verde II are excellent sources of iodine, iron, zinc, protein, hormones, and a wide range of trace elements, particularly cobalt, copper, boron, and manganese," they wrote in their report, published in the journal Science.

At least two of the species are used medicinally by local indigenous people to treat chest and intestinal ailments, Dillehay said.

He said it might be possible to take DNA from the chewed quids, but noted they were highly likely to have been contaminated since they were collected.

Last month researchers reported they had analysed DNA from 14,000-year-old human waste found in a cave in Oregon.