New England Antiquities Research Association

 

A&M Method Challenges Cave Painting Claims

Reprinted from the Houston Chronicle

by Eric Berger

 

 

 

July 2, 2003

 

They are pictures of people, deer, llamas, crocodiles and even pumas.

There are more than 350 stone walls filled with such paintings at Pedra Furada, a prehistoric site in a remote area of Brazil. They also may be the oldest cave paintings ever found in the Americas, and their discovery could radically change scientists' understanding of how and when the first people came to this hemisphere.

The problem is, a Texas scientist says the paintings, drawn with charcoal and other pigments, are not 30,000 years old, as a team of archaeologists led by Brazilian Niede Guidon there claim, but just a few thousand years old.

At issue is the method used to date the cave paintings, still very much a young field.

Scientists have long used radiocarbon dating to determine the age of old objects. Living organisms consume a rare form of carbon during their lifetimes and by measuring the ratios of these carbons in dead material, scientists can determine when the plant or animal died.

But most cave paintings were done with inorganic pigments -- reds, browns and yellows -- that cannot be radiocarbon dated because they lack carbon. Charcoal can be accurately dated, but it yields the oldest possible date because the charred wood used for the painting could have been dead or burnt long before being applied to a wall.

To tackle this problem, scientists can measure trapped electrons in the thin layer of calcium that builds up on cave paintings over the centuries. It's a proven method for dating stalactites and stalagmites in caves. But it's problematic for dating human art because limestone in cave walls, at millions of years old, can contaminate the calcium deposits and give a much older age.

Brazilian scientists recently used this method for setting the age of several Pedra Furada paintings at between 27,000 and 44,000 years old, backing Guidon's claim of a very old site.

To add validity to the findings, however, the Guidon team sent material to Marvin Rowe, a professor of archaeological chemistry at Texas A&M University, who has developed a novel method of dating cave art called plasma extraction.

Rowe's method is unique because he can extract traces of carbon within the non-living pigments, giving scientists a potentially powerful new tool to date cave painting.

In his lab, Rowe tested 12 mostly reddish paint samples and found ages ranging from 1,230 to 3,730 years ago, hardly eyebrow-raising dates for human habitation in South America.

"I was so disappointed myself because it would really have been a fantastic result," Rowe said.

Guidon did not accept the results, Rowe said.

Guidon was at the research site and unavailable for comment.

But the physics professor who performed the dating for Guidon, Shigueo Watanabe of the University of São Paulo, said he stands by the older dates. In an e-mail, Watanabe said he is flying this week to Pedra Furada to obtain a new sample of the calcium found in another area to date it.

He points out that there has been little independent verification of Rowe's technique.

Human occupation at Pedra Furada 30,000 years ago, let alone 50,000, would shatter scientific theories of the peopling of the Americas.

Until the last few decades the long-held belief was that mammoth-hunting humans crossed a Bering Sea land bridge about 12,000 years ago, based upon a notable archaeological site near Clovis, N.M., which dates to 11,500 years ago.

In 1985, an anthropologist at the University of Kentucky, Tom Dillehay, reported finding human artifacts at the Monte Verde site, in central Chile, that were 12,500 years old. The finding has led scientists to believe that humans were here earlier, and possibly came by boat rather than land.

Dillehay says his own excavations at Pedra Furada support people living there 11,500 years ago, but not earlier.

"We need to keep our minds open, but cautiously so," Dillehay said.

 

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