where chemistry meets archaeology
TRANSCRIPT
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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-
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