Prehistoric Fires Spark a Scientific Leap Forward

 

REHOVOT, Israel -- Somewhere, back in the mists of time, a primitive human realized how to light a fire. Suddenly, people could cook their food, keep warm in the cold, scare off predators, and, perhaps not least of all, gather around a central meeting place to enjoy one another s company after a hard day.

Cut to 1996. Those fires, and the people who sat around them, are long dead. The only memories of them remain in crumbling bones and tools and piles of dirt; our ancestors and all the complex doings of their lives have, as the saying goes, returned to dust and ashes.

And yet, for some people, the dust and ashes still breathe. Prof. Steve Weiner, a structural biologist at Israel's Weizmann Institute of Science, is one such person. In fact, he has spent the past decade studying dust and ashes -- and in the process has made a discovery that could move knowledge of prehistoric humanity several steps forward.

Weiner has discovered how to identify and analyze ancient ashes -- the most direct evidence of fire -- after they have almost entirely disintegrated. It may seem astonishing that, with science as advanced as it is, no-one could do so until now.

And yet this was the case: Ash is largely made up of unstable minerals that react and change constantly and are difficult to recognize even days after a fire goes out. Archaeologists have assumed certain sediments are ash, but until now there has been little scientific analysis of the composition of ash.

"What we found is that while most ash minerals do change over time, a very small component -- only about 2 percent of the original volume of the ash -- stays relatively stable," Weiner says."We know how to recognize this component now and can look for it, and we have a much better chance of proving something was ash even though it might not look like ash at all."

The discovery was made while Weiner was working in two prehistoric caves in northern Israel with postdoctoral fellow Dr. Solveig Schiegl, archaeologist Dr. Ofer Bar-Yosef of Harvard University, and geologist Dr. Paul Goldberg of Boston University. The finding is reported in the September issue of the Journal of Archaeological Science, and has already earned the 48-year-old South African-born Weiner a rare honor: He is the first Western scientist in 60 years invited to work at China's famous Zhoukoudian cave, home to the bones of Peking Man, believed to be among the first humans to use fire deliberately, some 500,000 years ago.

Weiner, who heads the Weizmann Institute s Environmental Sciences and Energy Research Department, admits he made the discovery almost serendipitously. He had chosen the Israeli caves -- which had been inhabited as far back as 250,000 years ago -- to study their rich collection of bones and artifacts.

He took with him a portable infrared spectrometer, a device that enabled him to analyze mineral samples on-site -- the first time this equipment, common in chemistry laboratories, was used at an archaeological dig. The device helped reveal that animal bones found piled in one cave, Kebara, were placed that way by the cave dwellers and were not a result of dissolution in some parts of the cave and preservation in others.

This led to the conclusion that Neanderthals were trend-setters in home design: they were among the first to divide their caves into separate areas of use, with a hearth at one end and a garbage dump at the other.

But when Weiner used the equipment in a second cave, Hayonim, he ran into a puzzle." I kept getting enigmatic readings on the spectrometer from all over the cave floor; I couldn t identify the major component of the sediments," he says. "It was only after some time that I realized I had gotten the same reading from some of the hearths in Kebara. That gave me the connection to fire, and I understood that this reading indicated ashes. Even though there were almost no hearths in Hayonim, there was ash all over the floor."

To test his theory, Weiner and his colleagues collected wood from local trees, burned it, and studied the results.

They found that a very small proportion of the ash was composed of a relatively stable group of ash minerals, known as siliceous aggregates. It was these siliceous minerals that made up a large proportion of the sediments -- in places up to three meters (9 ft.) thick -- on the floor of Hayonim and in the hearths of Kebara.The abundance of these minerals indicates that humans inhabited the caves intensively over periods of thousands of years.

"These caves were probably coveted real estate that were inhabited over a long period, and there is a lot to be learned here," Weiner says.

He and colleagues are now seeking to uncover the record of human habitation in the area by studying the sediment layers: They assume that ash would be present only in sediments from periods of habitation.In addition, the ashes and their surrounding sediments may throw light on changes in ecology, climate, and geology over the millennia.

At the same time, Weiner is busy analyzing samples he brought back from China this past May. He cannot yet say exactly what is in them: Unlike the well-preserved Israeli caves, Zhoukoudian has been cut open and exposed to the elements for years, and the sediments are diluted.

"At present scientists agree that Zhoukoudian was the earliest proven use of fire by man, based on evidence such as burnt bones and what was assumed to be ash," Weiner says. "I can t confirm or deny that yet; we re still analyzing samples."

Weiner is working on both the Chinese and the Israeli material with Drs. Bar-Yosef and Goldberg. They plan to return to China next May to try to complete the work. "Earlier investigators assumed certain things, based mainly on what they saw with the naked eye," Weiner says. "But we need to re-examine everything. We need to know exactly what the Zhoukoudian sediments are made of, and, if there proves to be ash, that it didn t come from a brush fire, but from one that was man-made and deliberate."

Meanwhile, applying science to archaeology has already shed new light on age-old secrets.