Alas poor Yorick, I know his age to the nearest five years

September 3, 1999

Henry Schwarcz's dating service is much in demand to fix the age of artefacts, including human skulls.

One could say that Henry Schwarcz has become a geologist-for-hire. Having produced the strongest evidence yet that humans lived in the Middle East before the last Ice Age, his skill at fixing a date to an ancient artefact has turned into a service sought after by archaeologists and palaeoanthropologists.

The path that took the McMaster University professor beyond the strict definition of a geologist - one who studies the earth's crust - came by way of a dating technique he pioneered that involves the teeth of animals hunted by ancient humans and the electrons they have accumulated from surrounding radioactivity.

When the Hamilton, Ontario, scientist started this work, studying 130,000-year-old skeletons and tools, there were very few ways to date the remains accurately.

"I guess I built a good mousetrap," says the Chicago-born professor. He says a void in archaeology needed to be filled, and his work with electron spin resonance, which measures electrons, seems to have done that.

This past spring, Professor Schwarcz was recognised for his "extraordinary contributions" in applying physics, chemistry and geology to archaeological problems by the Society for American Archaeology and given its Fryxell medal.

The technique in dating an ancient tooth, for example, sounds a lot more high-tech than the brushes and shovels of the archaeologist set.

After putting the sample inside the desk-sized ESR machine, Professor Schwarcz bombards it with microwaves and a magnetic field. A built-in computer then counts the number of electrons found in the tooth, accumulated from years of common radioactivity.

"In its crudest explanation, this means the stronger the signal, the older the sample," Professor Schwarcz says.

To understand the conditions that aged the sample, he measures those findings against the amount of radioactivity at the site. Through that equation, he can measure with relative accuracy the number of years the skeleton was lying in a site.

The teeth he studied, found inside a South African cave, gave clues to a more sophisticated Africa than Eurocentric archaeologists would have us believe, Professor Schwarcz says. The teeth were 70,000-80,000 years old.

Professor Schwarcz also studies ancient diet and directs a "small army" of graduate students and postdoctoral fellows.

On the day of this interview, he had received an email from a museum curator who had heard of his latest project, which involves the dating of human skulls.

If the curator brings the skull to Canada, Professor Schwarcz will be able to gauge its age "without cutting it up or chipping off any pieces".

With many of the skulls in museums around the world undated, this friend to archaeologists and palaeoanthropologists should soon also have his name in the address books of many curious curators.

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