The unearthing of artifacts can reveal much about the life and culture of ancient peoples, but it is an analysis of earth, not artifacts, that now has turned up evidence of a bustling pre-Incan silver industry in South America that had previously escaped the notice of archaeologists.

The new evidence -- uncovered by a pair of geologists rather than archaeologists -- suggests that mining and smelting of silver ore was done on a large scale in the Bolivian Andes 1,000 years ago, about 400 years earlier than the well-documented silver industry of the Incas.

"The fact that metallurgy is going on in that period isn't shocking," acknowledged Mark Abbott, a University of Pittsburgh geologist, "but its magnitude is surprising."

Abbott and a fellow geologist, Alexander Wolfe of the University of Alberta, report in today's issue of the journal Science that they found high levels of lead in the sediments of a small lake adjacent to a major silver deposit in southern Bolivia.

The high lead levels are an unmistakable signature of silver smelting, Abbott said, noting that the charcoal-fired, wind-drafted furnaces used to melt ore and extract silver through early colonial times produced clouds of lead. At Cerro Rico de Potosi, a rich mountain of silver ore, this lead would be carried on the wind from mountainside furnaces and settle into the nearby lake, Laguna Lobato.

The study of sediment cores, correlating different sedimentary layers with particular times, is a common tool for geologists, but its application to archaeology "is a real breakthrough," said James B. Richardson III, a Pitt archaeologist and a curator at the Carnegie Museum of Natural History.

But Abbott said he expects the findings to be met with a degree of skepticism, given the dearth of archaeological artifacts to support his conclusions.

"I'm sure we'll be hammered by archaeologists," Abbott said, noting that he and Wolfe study lake sediments primarily to record climate change, not to study cultures. He, Richardson and Pitt anthropologist Marc Bermann hope to do follow-up archaeological studies to find further nongeologic evidence.

"It's very surprising, but not impossible," Mary Van Buren, a Colorado State University archaeologist, said of evidence for pre-Incan silver industry. "People were there and they could have been doing this."

But Van buren, who has spent a decade studying silver metallurgy in an area near Potosi, said additional evidence of some kind -- remains of old smelting furnaces, for instance -- ultimately will be needed to prove that an intensive operation existed so long ago.

One of the problems with finding silver artifacts, said Ryan Williams, assistant archaeology curator at the Field Museum of Natural History in Chicago, is that it was so highly valued that it was never widely dispersed, but tightly controlled by elites.

Silver articles from the early era may also have been recycled by later cultures and, like any other silver piece, would be a favorite of thieves of any age. The Cerro Rico has been mined and remined so extensively that no evidence of ancient mining remains, Van Buren added.

The evidence uncovered by Abbott and Wolfe corresponds to the late stages of the Tiwanaku Empire, one of the first in South America. "We do not see much silverwork, if any, in the western Tiwanaku colonies," said Williams, who nevertheless described Abbott's work as "very exciting."

Van Buren, who has done most of her studies in Porco, about 30 miles from Potosi, said the Tiwanaku are known to have had intensive bronze metallurgy, so they probably would have been capable of silver metallurgy.

Though suggestions of a Tiwanakan silver industry run counter to the known archaeological records, other evidence from the lake sediments seems consistent with what is known about the later silver industry. Lead concentrations rise in sediments that date to around 1400, about the time the Incas are known to have begun their silver industry.

Also, the appearance of some silver in the sediments around the mid-1500s, when the Spaniards seized control of the silver mines, is consistent with tales suggesting that the Spaniards initially had trouble with smelting. Their furnaces reportedly burned too hot, Abbott said, causing some of the silver to be volatilized -- lofting silver particles into the air along with lead.

Lead was produced by the smelting furnaces because a lead ore, galena, was used as a flux -- a substance that would fuse with unwanted material in the silver ore to form slag, helping to separate out the precious silver.