Proving the Past

Archaeology once appeared to be the domain of science fictioneers. The digger merely seemed to exercise his imagination in reverse. Instead of forecasting the farout future, he re-created the long-lost past. From a few hunks of bones he built dinosaurs. In the ashes of ancient camp fires he saw the life story of extinct societies. He re-created primitive artifacts from the flimsiest shards. Today, says

British Digger Don Brothwell, he and his colleagues go even farther than that--but they guess even less. From aviation to atomic physics, from electronics to chemistry, a whole host of sciences now help archaeologists to extend their observations with astonishing accuracy.

Oldest Man. Atomic physics, says Brothwell in the current issue of Discovery magazine, can take a large share of the credit. When a manlike creature, Zinjanthropus, was discovered in East Africa three years ago, geologists from the University of California, using a potassium-argon isotope dating system, were able to show that flat-browed Zinjanthropus lived some 1,750,000 years back in prehistory, the oldest manlike animal yet found. By measuring the amount of potassium 40 and its decay product, argon 40, in a digger's find, scientists conceivably can fix an object's age at 50 million years, with a probable error of less than 2%. The radioactive carbon dating system, for which Dr. Willard Libby won a Nobel Prize in 1960, reaches back for only 50,000 to 60,000 years.

In the archaeologist's kit, there are more than a dozen other methods that allow him to date the objects he unearths. By measuring the electron emissions from reheated pottery with extremely sensitive instruments, scientists are able to determine when the pottery was first fired. This technique, called thermoluminescence, was used to date Greek pot shards from the Agora, near Athens, back to the 9th century B.C.

Obscure Elements. With the aid of atomic physicists, fragile specimens can now be subjected to chemical analysis without destroying them. At Brookhaven National Laboratory on Long Island, scientists have been bombarding archaeological finds with neutrons. Elements in pieces of pottery, for example, are thus made temporarily radioactive; and by observing their radioactivity scientists are able to identify them down to the tiny traces of rare elements. At Oxford and the Naval Research Laboratory in Washington, physicists have bombarded archaeological specimens with electrons, causing the specimens to give off X rays. By running a spectrum analysis on the X rays, the physicists are able to determine just what the specimens are made of. X-ray analysis has already allowed the Oxford researchers to uncover some archaeological frauds, including some 18th century copies of ancient Chinese porcelains.

"Archaeology," says Brothwell, "is no longer pure excavation. It has matured into a discipline demanding the cooperation of a variety of scientific fields." In their quest to extend history, archaeologists are using proton magnetometers to search for the ancient Greek city of Sybaris. They have used aerial photography to locate Etruscan tombs and to find a lost Andean road that was once part of a pre-Inca civilization. By analyzing the content of bone, they have shown Piltdown man for what he was--a forgery that fooled scientists for 41 years.

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