Romantic ideas of archaeology tend to be outdoors in nature,
adventurous excursions to lost cities, ancient tombs and, occasionally,
temples of doom. Chemistry, by contrast, rarely conjures up such
notions: Laboratory all-nighters with centrifuges whirring just aren't
But the relatively young marriage of these two
sciences - only a few decades old - has developed into a deep and
sometimes revealing relationship.
It was radiocarbon dating,
invented by University of Chicago chemist Willard Libby in 1949, that
gave archaeologists the ability to determine the "absolute age" of
unearthed artifacts.Mobile laboratories and new analytical technologies have carried chemistry into the field. It's now routinely practiced at most archaeological digs, said Joseph B. Lambert, a professor of chemistry at Northwestern University, used for everything from analyzing exploratory soil samples to ancient DNA.
"In the past, an archaeologist looking at a bit of pottery or a piece of marble could only tell so much," said Lambert. "Now, with access to tools like gas chromatography, nuclear magnetic resonance and polymerase chain reaction, they can chemically analyze that pottery or marble to determine its age, where it came from and what kinds of processes it has gone through. Chemistry reveals what can't be seen."
Chemistry helps archaeologists dig deeper.
Throughout history and the world, people have concocted fermented drinks, such as wine and beer. And not just for the taste, said Patrick McGovern, a molecular archaeologist at the University of Pennsylvania Museum of Archaeology and Anthropology.
Fermentation - a natural process that converts sugars into alcohol - helps preserve some food and beverages, McGovern said. It can enhance nutritional values. It possesses analgesic and disinfectant properties. And, of course, it produces mind-altering effects well-suited to certain social and religious functions. Or simply getting through the day.
"It wasn't easy living in ancient cities," said McGovern. "They were crowded, dirty, sometimes violent. Wine was a necessary social lubricant."
McGovern, who works in the Museum Applied Science Center for Archaeology in Philadelphia, has spent years tracing the evolution of fermentation, searching for clues to the first tipple.
At the moment, that appears to have occurred in China, at a place called Jiahu. There, McGovern and colleagues say they've found 9,000-year-old evidence of an alcoholic drink.
The actual drink, of course, is long gone. McGovern's evidence consists of analyzing residues extracted from fragments of pottery that once held liquids and comparing them with surviving liquid samples from a later period: the Shang dynasty, which lasted from 1200 B.C. to 1046 B.C.
Both samples contained trace amounts of chemicals consistent with making a fermented beverage of rice, honey and a fruit - either grapes or hawthorn berries, both of which grow in China.
These ingredients in combination would naturally ferment, said McGovern. The trick would be to stop the process before the wine turned to vinegar. That requires adding either another ingredient, such as tree resin, or sealing the liquid in an oxygen-free container, like a fired clay vessel. The Jiahu site is the oldest in China where pottery has been found.
McGovern's ultimate goal is to figure out how and why early cultures made alcoholic beverages, and what that says about human social development.
"Chemistry is absolutely essential to establishing that fermented beverages even (existed at the time). We can actually date and determine these products, instead of just depending on later historical records or inferences that aren't based on any real data.
"Then, depending upon the context of the discoveries, you can make inferences about the role fermented beverages played in ancient societies. You can create hypotheses and look for specific clues. Were the beverages used only in ordinary living? Were they used in cultic or burial practices? The evidence at Jiahu strongly suggests that 9,000 years ago fermented beverages had already become incorporated into many aspects of life."
Before the Inca Empire, there was the Wari - a militaristic, expansionist society that thrived in the Peruvian Andes from A.D. 500 to A.D. 1000.
The Wari were notably violent. Unearthed stone iconography, for example, depicts Wari warriors carrying or wearing decapitated heads. They were known to eat the bodies of vanquished enemy warriors.
In 2001, researchers from the University of North Carolina at Chapel Hill found direct evidence of the Wari's grisly ways: 21 trophy heads buried at a site called Conchopata near the city of Ayacucho in southern Peru. The heads had been severed, the brains scooped out and holes drilled through the crania and jawbones.
But the skulls were not solely those of enemy warriors killed in battle. Many, in fact, belonged to women, children and old people. Scientists didn't know what to make of the discovery. Was this evidence of a more benevolent side to the Wari? Did they, like other early cultures, practice some kind of ancestor veneration? Were these skulls the cherished remains of Wari mothers and daughters, sons and grandparents?
"It's been a huge debate," said Tiffiny Tung, a member of the North Carolina research team and now at Vanderbilt University. "Where did the Wari get their heads?"
Recently, a different group of scientists came up with a possible answer by measuring levels of a trace element in the skulls and in guinea pigs living in the region. Strontium is a radioactive alkaline earth metal found in rocks and soils, and by extension in plants and animals living in the region.
Kelly Knudson, director of the Center for Bioarchaeological Research at Arizona State University, looked at the ratio of two isotopes or forms of strontium found in the trophy skulls and in nontrophy skulls recovered in the same area. Because geologists did not have strontium isotope measurements for Conchopata bedrock, they used measurements taken from native guinea pigs.
In the skulls, Knudson and colleagues measured strontium isotope ratios in tooth enamel and in bone. The isotope ratio in tooth enamel remains constant throughout life, a reflection of where the person originates. The ratio in bone changes constantly, reflecting a person's recent history (for example, diet).
All the strontium isotope ratios detected in the nontrophy heads were similar, suggesting that their owners had all eaten food from the same geographic region throughout their lives. The trophy heads, however, displayed much more variability in their strontium isotope ratios. Those ratios also differed markedly from measurements in the Conchopata guinea pigs.
Such diversity, says Knudson, suggests the original owners of the trophy heads were not locals or cherished ancestors, but rather luckless victims of Wari raids upon enemy communities. The Wari took the heads of enemy warriors, but apparently considered skulls of all ages and genders to be trophy material.
There is a scene in the Bible (Mark 12:43) in which Jesus watches people making offerings to a temple treasury. The rich, he notes, give large sums of money and valuable gifts while a poor widow puts in just two small coins.
Jesus is more impressed by the latter, telling his disciples: "Truly I tell you, this poor widow has put in more than all those who are contributing to the treasury. For all of them have contributed out of their abundance; but she out of her poverty has put in everything she had, all she had to live on."
Such low-value copper coins are now known as "widow's mites," a reference to giving when one has little to give. In Biblical times, they were the currency of ordinary life, "used by everyday folks who didn't have gold or silver," said Mark Benvenuto, a professor of chemistry at the University of Detroit.
Because widow's mites were so commonplace, scientists presumed the coins represented fairly crude metallurgical technologies. Why, the reasoning went, would a society 2,000 years ago put much effort into making what essentially were pennies for the poor? It wouldn't make sense.
That thinking changed, however, when Benvenuto and colleagues analyzed 36 coins last year using a special kind of X-ray technology that can "see" about 100 microns (about 0.004 of an inch) into a solid object without any sort of cleaning or sample preparation. Called energy dispersive X-ray fluorescence, the technology beams X-ray photons at an object, then measures the distribution of energy among the affected particles, revealing what the object is made of. Benvenuto's analyses showed that the widow's mites were, in metallurgical terms, surprisingly advanced.
"They were a lot purer than we expected. There was a high percentage of copper, some tin, smaller amounts of what we would call slop - arsenic, antimony, zinc, lead. These guys didn't know about elements the way we do, but they weren't stupid. They knew that adding lead to the mix, for example, brought down the melting temperature so that they wouldn't need as much coal."
Understanding how coins were made offers insights into other aspects of long-ago cultures. For example, researchers at the University of Liverpool and the American University of Beirut are measuring isotope levels of lead and silver in more than 1,000 Roman coins. They want to know how much silver was used and where it came from.
Imperial silver coins were the financial backbone of the Roman empire, the currency of major trade. As such, Roman emperors sometimes manipulated the silver content of the coins to affect financial markets or to shore up government spending.
Historians attempting to explain ancient Roman economics and financial policy have long based their explanations upon superficial analyses of silver coins. Until recently, it was difficult to chemically analyze a coin without destroying it in the process. New chemical and isotopic tests leave the coins undamaged, but promise to reveal their true silver values and how Rome, like governments throughout history, manipulated money markets for their own purposes.