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Where Chemistry Meets Archaeology Reviewed by Mary T. Baker

" ^ ^ races of the Past: Unraveling the I Secrets of Archaeology Through I Chemistry" is an engaging ac­

count of the role of chemistry in archae­ology. In it, Joseph B. Lambert, professor of chemistry at Northwestern University, explores more than the use of chemistry to analyze culture and its evolution. He also reveals chemistry to be an essential element of that evolution.

The chemist's analysis of the remains of past societies, according to Lambert, does more than contribute to our knowl­edge of past human life. It also docu­ments the early development and impor­tance of chemistry itself. He revisits this idea throughout the book as he takes the reader on a tour through millions of hours of research in the field of archaeo­logical chemistry.

Many people might not automatically think of chemists as "analysts of culture," but most are not surprised to hear that chemistry can be used to illuminate the past through study of artifacts. Indeed, much less would be known about our past without chemists and their continu­ally improving analytical methods. Unfor­tunately, public perception of such work is usually of the "black box" nature, in which chemists, using arcane arts, infalli­bly pinpoint the maker of a particular neolithic tool, the date it was made, and its purpose. With another shake of the black box, the chemist might then infer the entire social structure of the tribe employing the tool, and even throw in the average temperature at the time, thereby also giving us an idea about glo­bal warming.

"Traces of the Past" gives its readers a peek into the actual world of archaeolog­ical chemistry and reveals the reality of this research: tedious data collection, careful development of testing protocols, cautious statistical analysis, and numer­ous reinterpretations of data.

A nonscientist reading this book might be a bit dismayed to find out that chemists' work is both more complicat­ed and less certain than that black box. However, such a reader is likely to soon become intrigued with the diversity of

information contained in artifacts and the various tools chemists have to coax it out. Deciphering an object's past from incomplete bits of (sometimes) vague clues can be a very engaging mystery.

Lambert literally works from the ground up, starting with the information chemists can wrest from stones and soil. Elemental and isotopic analysis can

"Traces of the Past: Unraveling the Secrets of Archaeology Through Chemistry," by Joseph B. Lambert, Ad- ; dison Wesley Longman, One Jacob Way, Reading, Mass. 01867-3999, 1997, 320 pages, $30 (ISBN 0-201-40928-3)

match a stone with its quarry, often with a reasonably high degree of certainty. Ra­tios of different isotopes and elements to one another provide a distinct "finger­print" for each source of stone. Pieces of a broken marble statue, for instance, identified through isotopic fingerprinting of the carbon and oxygen in them to have come from different sources, pro­vide evidence that the statue was re­

paired or had other additions made to it. Elemental fingerprinting of flint axes, when compared to flint from known flint mines, can indicate the existence of as yet undiscovered mines.

Elemental analysis of the soil around potential digs is used to supplement oth­er survey methods, such as aerial sur­veys, and sometimes even locates a set­tlement when other methods have failed. Concentrations of phosphate in the soil, for example, generally indicate human habitation, the phosphate coming from sources such as body wastes, refuse, and graves. Surveying the soil's elements can also shed light on a known site, helping to indicate which buildings might have been used to shelter animals and which ones humans.

Pottery has long been used by archae­ologists to document trade between groups of people in a particular area. Be­fore elemental fingerprinting became a fairly reliable way to link pottery with its clay source, archaeologists relied mostly on design elements to group and at­tribute pottery. But color, shape, and decoration can be copied; and they can evolve simultaneously in different settle­ments. Comparing elemental fingerprints of clay sources with those of pottery found nearby can give strong evidence of trade (or lack of it) between groups.

Chemists also rely heavily on spectro­scopic methods—mass, ultraviolet, visi­ble, and infrared. They usually use these methods to identify and characterize an object's components, rather than to link it to a particular source. For example, even though dyes found in textiles are more susceptible to the effects of aging than are pottery and stone, identification of these dyes can help determine what an archaeological textile must have looked like originally, which, in turn, gives a more complete picture of the people who made and used it. Because textiles and other dyed materials general­ly survive in lesser amounts than inorgan­ic artifacts, this kind of analysis has been aided by recent advances in spectroscop­ic methods that enable analysis of micro-samples. Although some dyes are specif­ic to an area, and so serve to link objects with their site of manufacture, most are common throughout an entire continent.

Analysis of organic materials often re­quires chromatography as well as spec­troscopy. Tree resins, for example, used to waterproof textiles, have very similar infra­red spectra, even when they come from different parts of the world, because they all contain similar terpenoid compounds.

OCTOBER 27, 1997 C&EN 57

Modern chemical tools help reveal the human past, but chemistry also played a key role in the evolution of human culture

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Gas chromatogTrtpiuwW^ apearumciriL· analysis of the resins will reveal trace ke­tones and alcohols that might be particular to one species of tree. Similarly, lipids in food residues can be characterized by their patterns of long-chain fatty acids, which can be separated by either gas or liquid chromatography.

Chemical studies of human remains— though controversial—are perhaps the most interesting. Carbon and nitrogen iso­tope ratios and trace elemental analysis in bone can provide information about diet. Carbon isotope ratios, for example, have been used to document changes in con­sumption of maize among native Ameri­can peoples, showing that the cultivation of maize came about at different times in various parts of the Americas.

Using chemical methods to date hu­man remains is not yet strongly estab­lished, but it has potential to yield the most useful information to archaeolo­gists. Amino acids racemize at a measur­able pace after the animal or person con­taining them dies, and the extent of race-mization of proteins extracted from archaeological bones can be a useful way to date such remains. In some cases, the method has yielded results that do not agree with other dating methods.

Electron-spin resonance and thermolu­minescence have also been used with some success to date bones and teeth, yielding answers based on the rate of free radical buildup that begins after the living tissue dies. These methods have been used to begin to place dates on stages of human evolution. For example, they point to an overlap in time between Neanderthal and modern humans, mak­ing it less likely that Neanderthals were ancestors of modern humans.

Modern, living humans can also be studied for chemical clues to the human past. The frequency of genetic variants of factors such as blood type sets a "genetic distance" between populations that can give an idea about how early humans mi­grated to populate the planet. Similarly, mitochondrial DNA studies can trace common ancestry of populations. Unfor­tunately, both of these types of studies have been seized upon by racial extrem­ists, who have tried to warp the results to fit their own political agendas, a re­minder to both chemists and archaeolo­gists that their work is potential fuel for political and social battles.

These are only some of the areas cov­ered in "Traces of the Past." Lambert's par­ticular insight is his suggestion that just as chemistry aids archaeologists in studying

the evolution of humans and their culture, archaeological studies also reveal the evo­lution of chemistry. Lambert sees chemis­try as having been critical to the evolution of culture. It's not enough to define hu­mans as toolmakers, he argues, since some nonhuman animals also use tools, and some—such as birds and primates—are even known to modify their tools. The real distinction between humans and oth­er animals, Lambert suggests, came when people learned to make chemical changes in their environment. Fire and the chemi­cal changes it produces in stone, pottery, and food were the first step. It was fol­lowed by manipulation of plant materials to make goods such as adhesives and per­fumes, fermentation of grains to make bread and beer, and the tanning of leather and dyeing of fibers for clothes. All of these discoveries earn our ancestors the distinction of being "the chemical animal."

"Traces of the Past" describes itself as being "for any reader intrigued by the in­terplay of science and history." It might make for dry and dense reading for a nonchemist, despite many short reviews on atoms, nomenclature, and reactions when these topics arise. Unfortunately, some of the explanations are oversimpli­fied, leading to at least one inaccuracy in

the description of polymers, particularly regarding acrylics in modern paints. How­ever, chemists will find the book interest­ing and be able to disregard any oversim­plified explanations. Because the book covers a spectrum of chemical specialties, even chemically trained readers are likely to appreciate having these reviews in the areas outside their own specialties.

The book offers a useful concentra­tion of methods, results, references, and figures in a field that is relatively new and has few books that give such a broad overview. Lambert, who has been work­ing in the field for more than 30 years, brings to it his experience and his repu­tation as a careful and thorough research­er. This reliability, combined with his choice of chemistry as the hero of the story of human cultural evolution, makes "Traces of the Past" pleasant, at times ex­citing, and informative. I suspect it will quickly become required reading in many graduate courses, and I recom­mend it for any chemist.

Mary T. Baker, a polymer chemist at the Conservation Analytical Laboratory of the Smithsonian Institution, studies the degradation of modern polymers found in museum objects and teaches chemistry of conservation.^

The art of mentoring "Adviser, Teacher, Role Model, Friend: On Being a Mentor to Students in Science and Engineering," National Academy Press, 2101 Constitution Ave., N.W., Washington D.C. 20418, 1997, 84 pages, $7.75 QSBN 0-309-06363-9), also available on-line at http://www.nap.edu/ readingroom/books/mentor.

Reviewed by Mairin B. Brennan

The importance of mentoring students in technical fields gained national at­

tention last year with the debut of the Presidential Award for Science, Mathe­matics & Engineering Mentoring. Ten in­dividuals and six institutions received the award in 1996 in recognition of their out­standing efforts to increase the participa­tion of underrepresented groups in sci­ence, mathematics, and engineering (C&EN, Oct. 7, 1996, page 38).

Some of those recipients returned to Washington, D.C, in September 1997 to participate in a symposium honoring the 10 individuals and nine institutions that received the award this year. They re­

counted the impact of the award on their mentoring efforts and the new­found recognition it earned them at their institutions. Meanwhile, however, facul­ty members elsewhere are struggling to find their mentoring feet, often at colleg­es and universities that have few resourc­es to train or assist faculty in becoming good mentors.

Now they have help. A guidebook compiled by the Committee on Science, Engineering & Public Policy of the Nation­al Academy of Sciences, National Academy of Engineering, and the Institute of Medi­cine should prove an invaluable resource. Aptly entitled "Adviser, Teacher, Role Model, Friend: On Being a Mentor to Stu­dents in Science and Engineering," the 84-page booklet is "intended for faculty mem­bers, teachers, administrators, and others who advise and mentor students of sci­ence and engineering."

Six concisely written chapters pro­vide a wealth of information on how to do a number of things. The following are among them:

• Break down communication barri-

58 OCTOBER 27, 1997 C&EN