Archaeological Classification and Analysis
Lesson Objectives: Understand lab processing of data and materials,
stone, ceramic, organic, human, and other remains; dating and other
analytical methods.
How do we do artifact and ecofact classification? Every science must begin with classification, but what are the bases we use to define different artifact types? Are they biased, and do they reflect what the makers of the artifacts thought? The obvious useful attributes are raw material (stone, metal, glass, ceramic, etc.), morphology (form, including size, shape, design, etc.), and style (more elusive—including design, decoration, etc.). Can we separate purely technological or functional aspects of an artifact from stylistic aspects? Can we look at the pure utilitarian function of an artifact but also the social and even ideological function? Let’s look at an artifact type in the classroom—your writing implements (have students hold up various ones). Most of them are long and skinny for functional reasons. What aspects might be stylistic? Even the color of the lowly pencil: what does yellow designate? Anyone have a pencil of a different color? What messages are on the pencils—printed company names, the university name? These messages are social, even ideological. We can do the same with pens. What does the expensive gold Cross pen show beyond pure function? Does it function better to take notes?
Can we learn of function, style, social and ideological implications from past
artifacts? Can we assume they will be similar to ours (no!). How does the archaeologist
interpret artifacts for which no function is obvious (such as a cache or hidden
pile of figurines, a burial with a pot over its head, and so on)? We can say,
“must be ceremonial!”
Here we will do a coin trick. One student needs to give me a handful of change (to be returned of course!) that we can lay out under the document camera or even on the table for all to see. We pretend that these are discoidal artifacts recovered in excavations from the planet Muni Mula, which we know was inhabited in the past by people. But we do not know what the artifacts are, so we start by trying to classify them. They are all round and made of metal, we can see. What bases do we use to classify? We can use size (arrange coins in descending order by size). Since in our culture bigger is better and more valuable, we might think that the biggest artifact is too (quarter) and that the smallest is the least valuable (dime). How about raw material? In our culture rare is more valuable, so we might assume the penny is the most important. How about whatever is pictured on the artifact? We cannot read the writing, but what is rarest? Most have long-haired men and buildings, but what about the new quarters? The Sacajawea dollar (or Suzy B’s, or liberty dimes) are very rare, and show women, so might we assume women are more important in this culture(!)? What other criteria to use? How about context, provenience. Many of these artifacts have come from large monumental structures (banks), but there are different distributions of the different types elsewhere. For example, large glass and metal machines containing traces of what might have been weird food remains have some of these metal discoidals, but not the copper-colored ones. We suspect those are even more important ritually or ceremonially because they seem to occur most often in caches inside ceramic animal effigy vessels in only one room of the domestic structures (piggy banks in kids’ bedrooms)! The exercise illustrates the problems with criteria for classification of artifact types in prehistoric archaeology.
What are artifact assemblages? The group of
all artifacts from a site, or from a particular temporal component of
the site, consisting of subassemblages based on finer and patterned
sets of artifacts representing human behavior. So the recent temporal
component of the site of our campus consists of assemblages of modern
artifacts, within which there might be a glass artifact assemblage,
a paper assemblage, plastic, etc. The faunal assemblage, animal remains,
would include discarded chicken bones, a few squirrel skeletons, etc.
The historic artifact assemblage underlying the concrete of campus might
include wooden and stone foundations of early hunting cabins and pasture
facilities, with a faunal assemblage of deer and cattle bones. The prehistoric
materials include a stone tool assemblage of spear points and a faunal
assemblage that also has deer bone.
What are diagnostic artifact types? Recognizable items that are found in particular time periods or places and give a cultural characterization. So a diagnostic artifact of the recent campus site component would be a plastic cup; of the historic component, perhaps an old china or stoneware mug; and of the prehistoric component, a sherd of a pottery vessel. Artifacts are usually first classified based on raw material type and technology.
What are lithic artifacts? A fancy word for stone, and the study of them includes other jargon such as debitage, French for the garbage of stone chips or flakes left by manufacturing stone tools. Why are stone tools the first kind described by the book? Not only are they the earliest artifacts we have for humans, being the best preserved, but also they do reflect our value system that is based on technology! What would be another way of classifying tools that did not involve technology? Here we can mention, for example, the categories used by historic archaeologists in the Southeast, such as domestic, architectural, etc., based on different kinds of human activity.
What other stone tool terminology is important? A blade is a flake that is at least twice as long as it is wide, and important for fancier stone tools. Retouching might be seen on a stone tool, chipping off of little flakes to make sharper edges or steeper edges for scraping instead of cutting or slicing. What stone tool types are important? Bifaces are flaked on both sides to get a nice edge, while many scraping tools are unifacial, flaked and shaped on one side only. Projectile point is the term for what most people call arrowheads, and even that is a value-laden term, because they might really be knives or other tools and not projectiles flying through the air. The flintknapper has just made a point of the type we call Florida Archaic Stemmed, estimated to be some 5,000 or more years old. There are many projectile point guides (show several) to use in North America to tell the approximate age of the point by its shape. Here is the Florida guide (Bullen 1975); we can also use the Alabama guide (Cambron and Hulse 1968), and there are others for states or regions (e.g., Justice 1987).
What attributes of stone tools can be studied? Raw material type can be determined in many ways, including physiochemical study of trace elements in the stone to establish the place of origin. Use wear studies look at the scratches and tiny chips and other signs of use on different materials: cutting meat leaves different patterns than cutting wood or hoeing soil. Residue analysis now includes even looking at traces of DNA in blood on the edges of stone tools to see what species of steak was being cut up!
Why does your book list ceramic artifacts right after stone? Fired clay artifacts also preserve well, are often the next-oldest kind recovered, and also reflect our Western penchant for classification based on technology. Firing clay to make figurines was known in the Upper Paleolithic, some 25,000 years ago, in Europe and elsewhere. Apparently this technology was then either lost or at least not used much until about 10,000 years ago, when people started making earthenware vessels for holding things, presumably mostly food, and cooking food. We still eat off plates that are mostly fired clay, unless we have paper or plastic or styrofoam!
What attributes of ceramics can be studied? Pottery is a more plastic medium, allowing the makers to incorporate more variability. If you make a mistake or change your mind when chipping stone tools you need to reshape the piece into something smaller or throw it away and start over. With pottery you can reshape the wet clay before you fire it, and even add things after it is fired, such as engraving or painting. There are many more pottery types than stone tool types, at least in southeastern U.S. archaeology. The standard artifact we find is a potsherd, a broken piece (pass some around), but what other things are made of clay? Figurines, spindle whorls, whistles, etc.
What are the raw materials for ceramic artifacts? Natural clays, of course, and also often temper or aplastic, some material added to the clay for various reasons, from the functional (better firing) to the stylistic. Who in the class has made pottery? What are the possible tempering agents? In the Southeast we find sand, grit (crushed quartzite), shell (crushed), and grog (crushed clay fragments, often probably old pots, maybe smashed in a fit of temper!). The earliest pottery in North America was tempered with plant fibers; in Florida this was Spanish moss, like we see hanging on the trees outside this building. The fibers burned out and left squiggly line open spaces in the clay (show example). Besides describing the clay minerals, the clay sources, and the decorative or surface treatment of the pot (stamping, incising, punctating, painting, etc.; show examples), we can determine something else about the manufacturing technology. In the New World there was no potter’s wheel. Early vessels were simply hand-built, like that first one you did in kindergarten. For the last 3,000 years pottery was made by the coil method, rolling a big snake-like form in your hands and coiling it around to shape the pot, then smoothing it. If we find a sherd of sand-tempered pottery that has uniform wheel marks on it at a Florida archaeological site we know it is from a Spanish olive jar, which very much resembles Indian pottery except for this technological clue.
What are fancier types of ceramics and how are they made? Old World technologies early produced fine china, vitrified clay we call glass, and fancy glazes able to be done because higher firing temperatures could be achieved. Does this mean New World peoples “lagged behind” and were not as bright as the Chinese or Egyptians? Maybe in glass manufacture, but does this mean in the rest of their technology or other areas of life? Remember that in this class we want to abolish the use of the terms “primitive” and “advanced,” since they are making ethnocentric judgements about cultures based on our own values, which place technology above nearly everything else!
Besides shapes, functions, and raw materials, we can also study residues on ceramics, as with stone or any other artifact. Ancient pots can sometimes still have food in them! What about pottery styles? Can we get at the meaning of some design on a pot that the potter intended? Given the opportunity for such variability, would the maker not put very individualized designs on these artifacts? Some archaeologists assume women made all the pots, and others, in a sometimes misplaced (I think) feminist approach, want to see the pottery designs as ways that always-oppressed women tried to empower themselves by their pride in self-expression. These are not always testable hypotheses in the far distant past, and we do now have many ethnographic examples of men making pottery and of women who have plenty of power already in their own cultures making pottery designs expressing far different ideas: religious, artistic, or just traditional design like the family always made.
What kinds of analyses can be done with metal artifacts? The same identifications of types, raw materials, trace elements showing places of origin, and studies of manufacturing technology. Early metalworking was done perhaps 9,000 years ago in southwest Asia with copper.
Why is copper earliest? It is available in some parts of the world as raw nuggets, and it is soft and easily shaped by heating. In a technique we call cold-hammering, Native Americans, for example, as well as many others around the world, could heat pieces of copper they picked up in northern Michigan and pound them into shapes of ornaments and tools. Pass around a piece of raw copper (I purchased this one at a museum shop). When a hotter fire could be made, copper could be melted and poured into casts.
What other metals were used early in prehistory? Silver, tin, and gold are soft and workable. Raw iron was rarely available from meteors. The process of making alloys was discovered thousands of years ago, probably in many places. Alloys combine two or more metals, and the most famous archaeologically is bronze.
What two metals make up bronze? What milestone do we name after bronze? Again, emphasizing technology, we note the Bronze Age because people discovered this combination of copper and tin had a lower melting point and cooled into a harder metal for making even more wonderful artifacts. Weapons, of course, would be nicer to have in a harder metal, especially for those who see technological development as completely linked to rise in military power (like the modern military-industrial complex, perhaps?). But there are many more bronze items with ceremonial and decorative functions, not to mention domestic utilitarian uses. The book shows (p. 126) 3,000-year-old bronze pots, and of course ancient bronze vessels in much of the Old World had to hold a lot of wine. I now pass around bronze replicas of pre-Roman Etruscan items, a coin and a little horse statue. The coin has an obvious set of functions (buy stuff, honor the ruler whose head is on it), and the horse may have been more than decorative if it was thrown into a spring as a spiritual offering. Look at the bronze fibulae pictures in the book (p. 127). Beyond the utilitarian function of holding up your clothes, they are of many different decorative styles that said something about your taste and probably status and position in life.
Why does iron metallurgy develop later and what milestone does it mark? The Iron Age began with development of a more complex technology, especially the requirement of a hotter fire, and of melting out the “bloom” and then reheating it and hammering it into shape. When you add charcoal, somewhat later in time, you get steel. There are many ancient technologies that we still have not been able to replicate in modern times.
What is special about gold artifacts? Gold is also soft and easily workable, and does not tarnish. If you have on, say, a ring someone gave you that you thought was gold and it is making a green stain on your finger, it is not pure gold! What kinds might you find in Florida? Of course, historic shipwrecks are known for Spanish gold, and while the silver coins end up looking like a blackish-gray rock on the sea floor, the gold is still gleaming. Because so many cultures value it highly, including ourselves, we love to study gold. So does Indiana Jones, who stole the gold idol at the beginning of the movie. Native Americans did have some gold and, especially in Central America, worked it into fancy forms. But usually in prehistoric Florida we do not find any gold, though we might get copper (show copper ear discs from a Florida site). One of our graduates who runs a contract archaeology firm in Orlando excavated a human skeletal hand with a gold ring on one finger. It was found in an area scheduled for a housing development and not known to be a cemetery. It was a recent historic burial, and the engraving on the ring led him to the person’s descendants, who still lived in the area.
What do we mean by organic artifacts? Anything made of something that was once alive, such as wood, shell, bone, leather, hair, horn, teeth, ivory, etc. I'm passing around a shell tool typical of Florida and some other coastal areas. The book shows bone harpoon heads (p.129). Of course, all these are of materials that are more perishable and less often found archaeologically.
What analyses can we do of organic artifacts? The usual, such as raw material type, manufacture, style; by now you should know the right questions to ask. Remember that the archaeological record is so biased in favor of what is preserved that we forget how important these artifacts are. But look at reconstructions at various sites, whether the Spanish mission site of San Luis in Tallahassee, with its European church but native council house and chief’s house, or perhaps the Forest Capital Museum’s reconstruction of a historic Florida homestead in Perry. All the buildings are of wood, the furniture, most of the tools and other artifacts are made of plant materials!
How do ecofacts differ from organic artifacts? They are not shaped into tools but are the result of human activity. The most typical are food remains, but there can also be naturally occurring remains affected by humans. For example, at sites where humans have cleared the forest to build houses, the natural pollen will not show tree species, but weeds that grow up in cleared areas.
What is paleoethnobotany? Study of plant remains from archaeological sites. It can be done at the macrobotanical level, looking at seeds, charcoal and wood pieces, etc. Some sites I have excavated have produced carbonized persimmon rind, native fruit skin that was dropped into the prehistoric fire and preserved for 1,500 years! At the microbotanical level we can study pollen remains, which is also known as palynology, and phytoliths, also known as biosilicates, which are mineral deposits that form in the open spaces inside plants (much like your pot for boiling water or your glass shower door in Florida will have scale form on it from calcium or iron in the water). Pollen is very distinctive for each species. This picture of pollen under the high-power microscope (in Fagan 1985) shows the grains looking like little alien spaceships. Phytoliths also have distinctive shapes based upon which species they form in.
What can archaeobotanical remains tell us? Besides what plants people may have eaten or used for other purposes, we can learn what was growing in the area or brought to the site. Pollen from species that are no longer present in the region gives us a clue to ancient ecosystems and climates, for example. The study of environmental change, especially as it is linked to human action, is enormously important today. We can also learn about the process of domestication of plants, where people change from gathering wild resources to producing their own. The latter is MUCH more work, so it is important to understand this.
How can we tell if plants were domesticated? What is domestication? Biological evolution; that is, genetic change, but through cultural, not just natural, selection. Genetic engineering is nothing new, it has been going on for 10,000 years or more. The only difference today is that we can do it inside the cell, with the DNA. But selecting what characteristics you want in a controlled, domesticated species is old, even if Gregor Mendel only described the process more recently!
What characteristics do humans want in their plants? Today we want hardier food crops, sometimes better taste, but often weirder things such as the square watermelons that the Japanese have produced that won’t fall off the truck or the “Flavor-Saver” tomato that can be picked when it is green and supposedly redden slowly enough to have a long shelf life and make money for the produce market (ask your grocer, and see if you think they have any flavor!). Besides food plants, we breed things for beauty and style—aren't they still trying to produce a truly blue rose?
What about prehistoric people’s domestication goals? They wanted more food, bigger, tastier, and easier to harvest. They bred out wild characteristics that allow the plant to reseed itself or otherwise propagate. Your book (p. 133) shows you the corn plant they began with, a small seed head on a grass, which is what corn is, and the big ear we ended up with after millennia of domestication. Corn is so domesticated that it cannot seed itself. It needs humans (or machines!) to open up the husk and plant the seeds.
What is zooarchaeology? The study of animal remains from archaeological contexts, with the same kinds of goals that we have for plant remains. What is the species, how was it used, what was its availability in the environment, and what about the domestication processes?
What faunal ecofacts might we see at a Florida site? Most common are shells from shell middens. But the zooarchaeological techniques we have today, including soil flotation and identifying tiny remains, show us that these prehistoric people were not just eating oysters and clams all day. In fact, if you order oysters in a restaurant, you get a huge platter with a dozen big shells, but the actual meat is a very small amount. So first of all, we realize that the amount of garbage associated with a species and the amount of meat it produces may not be proportional. With fine-screen recovery of tiny fish vertebrae we can see that Florida natives probably netted lots of fish for dinner, with only some oysters on the side. Zooarchaeologists have formulas to estimate meat weights based on the remains, and also to estimate the minimum number of individuals at the site. So one deer bone represents way more meat than a pile of oyster shells. Two deer leg bones, if they are right and left, could represent one deer, but if they are both from the left side then you have at least two deer. And so on.
What are coprolites? There is a lot of terminology associated with analysis of ecofacts, but this is the best word, meaning preserved feces, or dried-up old turds. A pile of animal bones and plant remains at a site can tell you what the people had at the site, but a coprolite is direct evidence of what someone ate, if it is a human sample. (This is also a cute word to know and use for many purposes!)
What kinds of human remains can be preserved archaeologically? Any and all, as we already saw from the discussion of site formation processes and human mummies in bogs, deserts, and wet sites. But usually human remains uncovered by archaeologists are skeletons or portions of skeletons. In Florida, when human burials are preserved the bones are often the consistency of cheesecake, even inside coffins, and hard to record or excavate.
What can we learn from human remains? From soft tissue there can be any kind of medical and biological study we want, from blood typing to DNA analysis, identification of stomach contents, height, weight, sex, cause of death, health and illness, trauma and pathology, diet, etc. We can get a lot of these from skeletons as well. Bone studies that identify chemical isotopes indicating what the person ate can tell us not only about diet and health, but also about past environments and socioeconomic systems that produced good or bad nutrition. Sex and gender issues in the past are also well addressed with skeletal remains, as are other social questions. We can also look at cultural modifications of the human body, such as piercings, tattoos, dental work, and cranial deformation resulting from binding the soft skull bones of an infant (pictured in the book, p.137).
What about the ethics of excavating and studying human remains? There is no discussion of ethics and professional responsibilities at this point in your book, and only a brief discussion at the end of the book where modern social issues are noted. But it is much too important not to discuss right now. The history of archaeology clearly shows that Native American skeletons and others from unmarked human graves were treated differently from those of the dominant society. Modern and even early historic cemeteries of white folks were protected; it would be illegal to dig up any graves without some kind of permission for a special reason. But unmarked graves were not covered by law until recently. The skeletons were treated as scientific specimens, just like the artifacts, to be studied in the lab. Anthropological archaeology recognizes that the descendants of the people whose remains are being studied may not agree to such study, and activism by Native Americans and other groups has succeeded in changing the laws.
The 1990 Native American Graves Protection and Repatriation Act (NAGPRA) requires U.S. museums and other institutions to return human remains and other cultural property, especially burial goods, taken without permission, to the people of their origin. New laws in Florida and most other states require archaeologists encountering unmarked human remains to report them to the state archaeologist and locate descendant communities with whom to consult about the disposition of the remains.
What does this mean locally? In Florida, for example, if I am digging and uncover a human skeleton, first I must determine if it is recent or not. If there is gold in the teeth, or a metal belt buckle or plastic, I call the sheriff and the coroner! If it looks like a prehistoric burial, I must contact the state archaeologist; but what about descendant communities? A Seminole Indian burial, which might have glass beads or other indicators, would be easier to deal with because we could call the tribe and begin consultation. They might want it not excavated at all, excavated and immediately reburied at their cultural center in Tampa, or they might allow certain studies such as those noted above.
With clearly prehistoric skeletal remains the picture is more complicated because there are no native Florida Indians left. They were exterminated by the early Spanish and other Old World conquistadors, through violence but mostly by introduced diseases. Into the empty land of Florida came Creek and other native folks from Alabama and Georgia, who with their African slaves and occasional Scottish traders evolved into the Seminoles of the eighteenth century. So there are no clear representatives of Florida native peoples to consult with about prehistoric remains, and a determination must be made in each case by several interested parties, including modern Indian groups. We will return to these issues later in the class.
What can we learn from soils and sediments excavated by archaeologists? Rivers, lakes, different kinds of wind, water, and erosional action produce different soils that may give us clues to past human and natural action. This is why site formation processes are important to know. For example, a Florida hurricane might produce a nice culturally sterile white sand layer on top of a dark organically stained midden zone, sealing the midden nicely. Understanding soil deposits helps us reconstruct the original landscape of the site.
What do you think is meant by micromorphology? Inexplicably placed in later discussions in your book (see p. 185), it is the study of microscopic traces of soils and sediments to determine localized information, such as use of individual rooms within excavated houses or activity areas at sites. This is real detective work; microscopic traces of feces or pollen or other materials can help assign functions to certain places within sites.
What information does a cultural feature produce? As we already discussed, features can range from small postmolds and pits to large buildings. Some are constructed by humans while others may be accretionally deposited by human action, like garbage dumps. Analyzing spatial layout, construction technology, and associated artifacts and sediments can give everything from purely functional to social information. The carbonized fruit skin I mentioned from a Florida site came from a garbage layer which has other information about seasonality. This layer also had duck bones in it. Because the persimmon fruit is ripe in the fall and ducks arrive in the fall (to be shot for a nice dinner), we know the prehistoric people must have lived there in the fall. This is supported by a different line of evidence, namely that the site is on the riverbank and the river floods every winter and early spring today. Flood deposits are evident in the prehistoric garbage layer as well, so we know it would be easier to live in this spot during summer and fall during its occupation 1,500 years ago too.
How does an archaeologist get a date? Dating the past can be done with several different methods that are well-explained in your book (chapter 7).
What is the difference between direct and indirect dating? Direct methods date the artifact itself, while indirect methods date something it is associated with. It is seldom possible to date a stone tool or a clay potsherd, for example; radiocarbon dating requires something with carbon in it. But we might date the charcoal next to the stone tool or sherd under the assumption that they are the same age.
What is the difference between relative dating and absolute dating? Relative methods give an age only in relationship to something else, while absolute methods give a calendrical date. An easy relative method to understand relates to the law of superposition; deeper things are older than shallower things, but we do not know absolute ages.
What are some types of relative dating? Artifact seriation is done by arranging artifact types according to their stylistic similarities and/or frequencies of occurrence. See the nice figures in your text showing both twentieth-century automobile designs (p. 149) and Sir Flinders Petrie’s stylistic seriation of ancient Egyptian pot types (p. 151). We may not know the absolute dates, but we can arrange the styles that look most similar closest to each other on the chart. What is the disadvantage of this method? First, it assumes gradual change through time and would not work with everything (look at the radical shift from slide rule to pocket calculator, or from pocket notebook to PalmPilot—those artifacts do not look anything alike!). Second, you can see gradual change through time, but you don’t know which end is up! Which is the earliest and which the latest?
Frequency seriation arranges artifacts based on frequencies, assuming that types gradually come into popularity and gradually fade out. The very nice chart of New England tombstone types on p. 152 shows how a frequency seriation can produce battleship shaped curves. The tombstones have the dates on them, but you could also do this with artifact types arranged by vertical stratum. The curves look like battleships in plan view, or portions of battleships; hence the name. The tombstone study of Deetz and Dethlefson cited in your text is a famous one because it shows stylistic change through time that can be correlated with social and ideological trends. Look at the three kinds of tombstone motifs in the chart: the death’s head, cherub, and urn-and-willow pattern. All three fit nicely in the half-circle of the top of the tombstone, so in terms of design, we have the constraints of shape to consider. Within that shape, however, the winged, skull-like death’s head gives way to the happy little winged angel, then the asymmetrical design of an urn with the flowing, still wing-like fronds of the willow. What does this say about the living people commemorating their dead loved ones? They are going from a more harsh, New England-style Protestant view of hellfire and damnation to a more benign view of heavenly bliss, then to a totally secular decorative motif that suggests waning power of religious beliefs!
What is fluorine dating? It is a relative dating method described in your book along with other bone chemistry relative methods on p.158. It is based on the principle that two bones buried together at the same time will take up the same amount of fluorine (and other elements) from the soil. It is famous because it is the method used to expose the hoax of the notorious “Piltdown man” fossil. Many textbooks in the 1970s and 1980s removed the story of Piltdown, which was too bad because it is fun and also packed with social and scientific meaning. It has been put it back in again since the 1990s, but needs more explanation because it says so much about the influences of world politics and intellectual arrogance in anthropology. The Piltdown skull and teeth were found in England between 1911-1915 by amateur paleontologist Charles Dawson, who convinced all the big famous men, and they all were men, in anthropology that they represented the “missing link” creature evolutionarily placed between apes and humans. No other finds resembling Piltdown were unearthed, and over the decades the australopithecine early hominid remains coming out of south Africa began to convince the scientists that the earliest humans originated in that continent from apelike ancestors. By the 1950s, when fluorine dating proved the skull to be a fake, few believed in it any more. It was a cranium (head without lower jaw) of a modern, if old (maybe Roman?) human and the lower jaw of an ape, filed to fit together and dyed to match! But the two did not have the same amount of fluorine. Who did the hoax? We are not sure. Dawson died shortly thereafter, and other possible perpetrators have been suggested, including Teilhard de Chardin (a famous Catholic priest and evolutionary thinker who may have been a young prankster at the time) and Sir Arthur Conan Doyle (author of the Sherlock Holmes stories). But meanwhile, we also need to ask why the fossils were so readily accepted as human ancestors. First, they fit the expected picture of a large braincase and ape-like jaw. Now we know that brain size was the last thing to evolve, and that early human forms are recognized by their upright, bipedal skeletal structure. Second, where was Piltdown found? In England, the home of so many of the major thinkers who accepted it, and easier to see as the home of the earliest humans than Africa, where the people are dark and considered inferior!
What is the difference between absolute and chronometric dating? Absolute dating means the calendrical date can be known. It is pretty rare and usually only possible with things that have dates on them, such as newspapers or coins. Your book does not give the term “chronometric,” but it is important to differentiate and not quite absolute. Chronometric means measuring time since something has elapsed. Most of the dating methods we use in archaeology are chronometric; examples follow.
Most people have heard of radiocarbon dating; how does it work? Invented by Nobel Prize-winning physicist Willard Libby in the 1940s, this method is based on the radioactive decay of the carbon 14 isotope (written as 14C). All living things take in carbon through food, breathing, etc. The proportion of the carbon 12 isotope to carbon 14 is known, and after the organism’s death the radioactive decay takes place at a known rate, measured by the concept of the half-life. This means, for carbon 14, with a half life of 5730 years, that after that many years only half will remain to emit radiation. The radiation can be measured and the time elapsed since the organism’s death calculated. The advantage of the method is that there is often charcoal, bone, or other organic material that can be dated, and this method is usually the most important for archaeology. The disadvantages are that you have to have something organic, not stone or pottery, and you have to have enough of it to date (about a cup of charcoal or, for dating a large animal or human skeleton, an arm and a leg!), and you have to have about $300. Another disadvantage is that the date comes out as a statistical approximation within two standard deviations, so there is something like a 33% chance that it is not correct. Another disadvantage is that farthest back you can date things because of that half-life is about 40,000 years, so that the human experience before that, some 2 million or more years, is too old to date by this method. This is fine for North and South America, however, because apparently there were no people here that long ago.
What is AMS radiocarbon dating? The letters stand for accelerator mass spectrometry, and this technique is a wonderful refinement that allows the physicist with a big particle accelerator machine to count the actual carbon atoms. Therefore it needs far less material for dating, such as a piece of charcoal as big as a pencil point tip. This can be a great advantage when there is not good organic preservation at your site. From our USF excavations of a shell midden in Florida, we obtained a sherd of fiber-tempered pottery that broke open to show a couple fibers of Spanish moss still unburned and undecayed in the clay. These were dated by the AMS method—one of the rare times that we COULD date a potsherd in this fashion. The date returned was about 4,000 years before the present.
There is yet another disadvantage of radiocarbon dating that has lately been corrected by utilizing a totally independent chronometric method, known as dendrochronology. What does this word mean? Tree ring dating, using sequences of thick and thin rings from trees with overlapping lifetimes and working backward in time. We can even find living trees that are several thousand years old, and your book shows a picture of one of these, the gnarly old bristlecone pine from the southwestern U.S. Ring characteristics depend on annual weather patterns, so this method works best where there is great variability, as in the southwestern desert. Disadvantages of the method are that you have to have enough wood, and the wood the artifact was made of may have been old already when used, or used for a long time, as in a house beam.
How has dendrochronology changed radiocarbon dating? The great gift of tree-ring dating has been to help correct the errors in radiocarbon dates and provide a cautionary tale of science. The assumption was that uniform amounts of radioactive carbon were present every year in the atmosphere and absorbed by all living things. When someone decided to check this by radiocarbon dating individual tree rings with known ages, it became clear that past levels of carbon 14 have fluctuated a lot. Now whenever you get a radiocarbon date, it is corrected or calibrated along a curve produced by tree ring dates to give a more accurate calendrical age.
What other dating methods are important for archaeology? Several other chronometric methods are based on measuring time elapsed since some physiochemical change. Most important is potassium-argon dating which again measures decay of a rare radioactive isotope of potassium that results in its becoming argon gas. Here the half-life is 1.31 billion years, so much older things can be measured. But you need something that has the requisite minerals. Luckily, there is potassium in volcanic deposits that have contained early human fossil forms in east Africa, so many of those finds have been so dated.
What is archaeomagnetism? Another chronometric dating method that is based on the fact that the earth’s magnetic fields shift over time. When soil or clay is heated, the iron particles in it align themselves with the poles. Since north moves over time at a known rate, we can measure the magnetic alignment in the ground and compare it with today’s. The method is often used in the eastern U.S. when we encounter hearths or fire pits with burned clay. You isolate a small cube of soil in the ground and cover it with plaster, on which you mark the current compass north. Then you cut it out of the ground and send it for archaeomagnetic dating, and they will see how the alignment of the iron particles in this soil cube compares with the current alignment of north. Again, the disadvantages are that you have to have burned soil with iron content. The advantage is that it is not difficult or too expensive.
Which dating method is best to use? Since there are advantages and disadvantages for all of them, the very best strategy is to use more than one independent method. Radiocarbon is the most important for the New World and later Old World prehistory, but if you can confirm your radiocarbon date in some other way, your results are much more reliable. At a site in northwest Florida where we were working during 2002, we had already excavated typical prehistoric pottery that has been dated often to between A.D. 1200 and the time of European contact when we got that tiny glass bead from the fine screen of the flotation machine. We know the Native Americans had no glass until the Spanish brought it in the sixteenth century. I found enough charcoal to get a radiocarbon date from a small pit feature that had the bead in it, and the date was returned as about A.D. 1500—very early in historic times (White 2000). There are no historic records for this part of Florida that early. So I am returning to dig a little more and see if more accurately dateable evidence might be found.