A team of archaeological scientists in the United States and Germany say they have developed a technique to accurately determine the age of stone tools and artifacts between 50,000 and 100,000 years old, a period that has proved particularly tricky to map with other methods. If it's accepted by archaeologists and anthropologists, the technique could result in a clearer picture of the era and even lead to new discoveries about the civilizations that thrived in that period.
     "Our objective is to close the chronological gap that is so critical to paleoanthropology," said University of California at Irvine professor Jonathan Ericson, who helped form the project. "The process will allow people to refine chronologies that have not been able to be refined because of the limitations of current techniques."
     The new technique, called quartz hydration, takes advantage of the natural properties of quartz, a mineral found in many rocks. Whenever a rock containing quartz is cut or polished, perhaps for a statue or ax head, the quartz at the surface is left exposed. Over time, water diffuses into the quartz, forming a layer. By measuring the layer, Ericson and his team members found that they could determine how long ago the rock was cut. The technique can be used to date artifacts that were created between 100 and about 100,000 years ago, Ericson said.
     The group verified their theory by measuring the hydration levels on various artifacts with known ages, including Olmec pendants from Mexico and belt buckles from Austria. They also conducted tests on 100,000-year-old objects found on Lukenya Hill in Africa. The downside, of course, is that the new technique can't measure the age of organic material, like human remains or wood.
     In comparison, the most popular technique for determining the age of archaeological finds, radiocarbon dating, is only effective for objects that are less than 50,000 years old. It is also limited to organic matter, and therefore can't be used on stone tools or statues. Another technique, potassium-argon dating, works on minerals, but tends to be accurate only when artifacts are between 100,000 and 4.3 billion years old.
     "Until now, archaeologists have had to rely primarily on techniques like stratigraphy" - estimating an object's age depending on how deep it is buried in relation to other objects - "to determine the age of artifacts in the 50,000-to-100,000-year period," said Ericson. Because they rely on estimation, relative techniques like stratigraphy are considered less precise than absolute techniques, like radiocarbon dating. Ericson cautioned, however, that quartz hydration is not a complete replacement for absolute or relative techniques. Indeed, quartz hydration is temperature-dependent, meaning that a researcher must first know the conditions in which a given artifact was created and buried to get an accurate measurement of its age - information that may not always be available. But even this has its benefits. Ericson said he imagines that scientists could use measurements of quartz hydration along with the known age of an artifact to figure out the historical temperature at an archaeological site. The technique might have other benefits, too. "This could be useful in art history, for detecting forgeries," said Ericson. "If you have quartz artifacts, you can see what's been made recently and what's actually very old."
     Ericson estimated the cost of the quartz hydration technique to be $500 to $1,000 for each artifact. He added, though, that the overall cost could vary because the measurements must be performed with the help of multimillion-dollar particle accelerators.

Sources: Todai@UCI (12 April 2004), Wired News (14 April 2004)