Kenneth L. Feder McGraw-Hill © 2004 The McGraw-Hill Companies, Inc. All rights reserved. C H A P T E R Probing the Past 2 The Past in Perspective

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 2 Probing the Past Epistemology: How We Know What We KnowEpistemology: How We Know What We Know Paleoanthropological and Archaeological SitesPaleoanthropological and Archaeological Sites Analyzing Archaeological Data Determining the Age of a Site or Specimen Summary

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 3 Epistemology: How We Know What We Know The “Science” in the Study of the Past –Science often begins with objective observation of the world or universe. Anthropologists concentrate on humanity. Paleoanthropologists archaeologists focus more specifically on the human past. –Scientists come up with general explanations, or hypotheses, for what they have observed. They also need to test these hypotheses by predicting what other data will be found if a hypothesis is valid.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 4 Paleoanthropological and Archaeological Sites Paleoanthropological and archaeological sites are places where physical evidence of a past human presence can be recovered. –The skeletal remains of human beings or human ancestors –Artifacts—objects made and used by past peoples –Ecofacts—environmental elements that exhibit traces of human use or activity Sites are defined by the recovered objects themselves and by the physical arrangement of the remains.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 5 Paleoanthropological and Archaeological Sites How Sites Are Formed –Taphonomy—The study of how paleontological remains ended up in a particular place. Features—Clusters of archaeological material that can be analyzed in our attempt to reconstruct a particular activity or set of behaviors. Primary refuse—When the items used together and deposited together are left exactly where they fell by ancient people. Secondary refuse—Deposits where people took their trash to a pile or pit, removing it from the immediate vicinity of their living quarters.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 6 Paleoanthropological and Archaeological Sites How Sites Are Preserved –Once material objects are laid on or in the earth, natural processes may cover, protect, and preserve them. How Sites Are Found –Many of the sites have been exposed by erosion. –Scientists search for sites through a process of subsurface sampling, placing test pits at regular intervals. Sophisticated remote-sensing devices—ground- penetrating radar, proton magnetometers, or electrical resistivity meters, can help search for sites.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 7 Paleoanthropological and Archaeological Sites How Information Is Recovered –A single artifact, devoid of any context, provides only a fraction of the information provided by an object for which context has been preserved and recorded.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 8 Analyzing Archaeological Data How Artifacts Are Analyzed –The Sources of Raw Materials Determined through trace element analysis in which impurities in tiny or “trace” amounts are scanned for. –Uses procedures such as neutron activation analysis and x-ray fluorescence. –Tool Manufacture and Use Experimental replication is the process of attempting to authentically re-create ancient artifacts. Morphology is the form of the object, what it looked like, and by the evidence of wear patterns. –Social Patterns

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 9 Analyzing Archaeological Data How Ecofacts Are Analyzed –Many archaeology labs possess osteological comparative collections, or bone libraries, where ancient specimens can be compared to known labeled specimens. –The minimum number of animals represented in the faunal assemblage at a site can be reconstructed. –Most animals exhibit two distinct forms on the basis of sex—sexual dimorphism.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 10 Analyzing Archaeological Data How Ecofacts Are Analyzed (continued) –Animals go through a number of osteological developmental stages—changes in their bones as they grow and mature. Plant remains, including seeds, nuts, and wood, can be recovered and analyzed, and the contribution of plant foods to the diet can be assessed. –We usually can differentiate the seeds, grains, or fruits of wild species from those that have been altered by humans through artificial selection in the process of domestication.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 11 Analyzing Archaeological Data How Ecofacts Are Analyzed (continued) –One of the most important sources of information about past plant communities is pollen, the male gamete in plant sexual reproduction. Percentages of the various kinds of pollen falling on a site when it was occupied can be calculated from an ancient soil layer. –The researcher attempts to locate modern locations where the pollen rain—the percentages of different plant species that rain down in the spring today—is a close match for the percentages derived for an ancient time and place.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 12 Analyzing Archaeological Data How Ecofacts Are Analyzed (continued) –Palynology provides a vital, direct link, to the plant communities that characterized given places and times. –There are a number of different photosynthesis pathways. These pathways differ in how they treat the different varieties (isotopes) of carbon in the atmosphere. –Planet-wide changes in climate can be read in the oxygen isotope record preserved in the fossil shells of ancient marine microorganisms called foraminifera (forams).

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 13 Analyzing Archaeological Data How Human and Prehuman Skeletal Remains Are Analyzed –The bones of human ancestors can: Inform us about how human ancestors walked. The kinds of climates to which they were adapted. The foods they ate. Their general level of nutrition. The diseases and traumas from which they suffered.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 14 Analyzing Archaeological Data –The Species Represented by a Bone –The precise form of each of the bones in an animal’s body is unique to its species. –The Sex of a Skeleton –Among humans and apes, males tend to be larger, with heavier, denser, and rougher bones and larger, heavier skulls, than females. –The various angles of the pelvis that control the overall size of the birth canal are, of necessity, larger in the vast majority of females than in males. –The Age of Death –The deciduous dentition—the baby teeth—erupt above the gum line in a regular order and at fairly well established times.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 15 Analyzing Archaeological Data –The age of death... (continued) –When we are born, each of the long bones in our extremities is in three sections: a shaft, or diaphysis, and two endcaps, or epiphyses (sing., epiphysis). –In a process called epiphyseal fusion, the shafts and endcaps fuse to one another during growth at more less set times during our teen years. –Cranial sutures—the places where the different cranial plates come together—fuse through time. –The region where the pubic bones come together—the pubic symphysis—can also be used to estimate the age at death of an individual.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 16 Analyzing Archaeological Data –Geographic Origin –Skeletal traits vary geographically. –Pathology and Disease –The bones in a human body are like a book on which some of that human’s life experiences are written. –These marks can be read by the specialist in paleopathology. –Preserved Bodies –Nearly intact bodies 2,000, 3,000, even 4,000 years old have been recovered from Danish peat bogs (Glob, 1969).

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 17 Analyzing Archaeological Data These diagrams show epiphyseal fusion for human beings and the age order of tooth eruption. Careful analysis of skeletal remains can reveal species, sex, age at death, nutritional status, cause of death, and geographic origin of the individual. Insert Figure 2.10 (old figure 3.8)

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 18 Determining the Age of a Site or Specimen Dating Techniques Based on Radioactive Decay –Until recently dating fossils and sites depended on sequences based on stratigraphic layering of the earth’s surface. –Researchers can now rely on radiometric dating techniques based on the know rates of decay of several radioactive (unstable) isotopes (varieties) of common elements. These techniques provide absolute dates rather than relative dates.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 19 Determining the Age of a Site or Specimen Dating Techniques –Researchers can... (continued) K/Ar Dating –Has been particularly useful when applied to early human ancestors. –A new version of the technique, 40 Ar/ 39 Ar, is more accurate and is used more often than the older procedure. 14 C Dating –All living things on earth are part of the carbon cycle and maintain the same proportion of stable 12 C to unstable 14 C during their lifetimes—a proportion that is, in turn, the same proportion as is seen in the atmosphere. – 14 C decays at a regular, naturally fixed half-life—in its case, 5,730 years.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 20 Determining the Age of a Site or Specimen Dating Techniques –Researchers 14 C Dating... (continued) –For radiocarbon dating (carbon dating, 14 C dating) to produce accurate results, the item being dated needs to be at least a few hundred and ordinarily less than about 40,000 years old. –Accelerator mass spectrometry (AMS) may ultimately extend the viable dating range back 10,000 to 30,000 years beyond this.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 21 Determining the Age of a Site or Specimen Dating Techniques Based on Biology –Dendrochronology, or tree-ring dating, is an extremely accurate biological dating technique. By overlapping ring sequences of living trees with those of old dead trees, a master sequence of tree- ring width variation over many years has been developed. –The calibration curve, now extending back to 11,000 years ago, allows a radiocarbon date within this period to be converted to a calendar year date.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 22 Determining the Age of a Site or Specimen Calibration curve for radiocarbon dates. The vertical axis represents the radiocarbon dates derived for a large number of tree-ring samples, and the horizontal axis represents the actual dendrochronologically derived dates for those same tree rings. As you can se, for tree rings that are more than about 3,000 years old, radiocarbon dates generally understate the true age of a sample. Insert Figure 2.13 (old figure 3.10)

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 23 Determining the Age of a Site or Specimen Dating Techniques Based on Radiation Damage –Electron spin resonance dating (ESR) is one of a number of techniques that date materials through the measurement of radiation damage, in this case, the buildup of electrons trapped in crystalline materials at a site (Grun 1989, 1993; Grun and Stringer 1991).

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 24 Determining the Age of a Site or Specimen Dating Techniques Based on Radiation Damage –Luminescence dating measures the amount of energy that is trapped in material recovered at archaeological sites as a result of natural radioactive decay in the surrounding soil. The amount of energy captured by the archaeological material over time can be measured after releasing the energy by heat in the application called thermoluminescence, or TL) or by laser light (in the application called optically stimulated luminescence, or (OSL).

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 25 Determining the Age of a Site or Specimen Dating Techniques Based on Radiation Damage –Fission-track dating bases aged estimates on the number of visible “tracks” left by radioactive decay in site materials. Dating by Measuring Chemical Processes –Obsidian hydration measures the regular buildup of a “hydration layer” on freshly exposed volcanic glass.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 26 Determining the Age of a Site or Specimen Dating by Measuring Paleomagnetism –Paleomagnetic dating is based on the fact that the position of magnetic north has fluctuated over time.

McGraw-Hill© 2004 The McGraw-Hill Companies, Inc. All rights reserved. Slide 27 Summary How sites are formed, how they are preserved, and how they are discovered are key questions for archaeologists and paleoanthropologists. Past peoples can be investigated directly through analysis of their physical remains, which determines the age, sex, and health status, and geographic origin of ancient individuals.