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Chapter 3Archaeological Dating Methods“Everything which has come down to us from heathendomis wrapped in a thick fog; it belongs to a space of time wecannot measure. We know that it is older than Christendom,but whether by a couple of years or a couple of centuries,or even by more than a millennium, we can do no more thanguess”Rasmus Nyerup, 1802
The Need for Reliable DatingThe calendar date of an archaeological event or artifactis one of the most important pieces of information to bedetermined in archaeology. These calendrical dates arethe skeleton that link historical events and correlate anddefine archaeological findings within the historical context.Several methods have been developed to determine theage of archaeological samples. They vary from systematiccategorization based on ornamental and artistic structureof artifacts initially, towards a wide range of more sciencebased methods. The latter have mostly been developedduring the second half of the twentieth century as uniqueapplications of scientific methods that have been developedin biology, chemistry, and physics.
Archaeological Clocks Biology Dendrochronlogy( 7 000 y) Chemistry FUN testAmino-Acid clockHydration and Diffusion( 100 000 y)( 100 000 y)( 100 000 )y Physics Archaeomagnetism,Oxygen isotope ratios(8000 y)(1 M y) RadioactiveDating 14C( 100 000 y)( 100 000 y)(500 000 y)(50 000 – 10 M y)(100 - 30 000 y)(1000-1 M y)methodK-Ar methodUranium-seriesFission trackingThermoluminiscenceElectronspinresonance
DendrochronologyDendrochronologyor tree-ring datingis the dating of pastevents through studyof tree ring growth.Trees showing sensitive rings are affected byslope gradient, poor soils, or too little moisture.Trees showing complacent rings have generallyconstant climatic conditions such as high watertable, good soil, or protected locations.
Building a calibration curveEach vertical line in the above graph representsone year. The yellow bars that appear on threeof the graph's lines represent narrow rings. Thenarrower the annual ring, the longer the line.The "b" indicates a year with an unusually widetree ring, a dashed line marks a year where thattree failed to produce a visible ring.
Building a chronology
Dating oldpaintings!PaintingPortrait of a GentlemanPortrait of a Young GirlPortrait of H. MelberTotal Rings163145146Last Ring152115191520External Datesigned 1528attrib.1520signed 1526 years
A triptych by Rogier van der WeydenThe right panel is in the Metropolitan Museum of Art in New York.The remaining two-thirds in the Capilla Real, Granada. A secondtriptych is in Berlin. The Metropolitan-Granada altarpiece was thought,on art historical grounds, to be the original and the Berlin altarpiece a copy.
Analyzing the tree-ringsThe Berlin altarpiece has a last preserved ring from 1406. With a mediansapwood allowance of 15 years, the felling date should be around 1421,early in Rogier's career. The wood of the Metropolitan altarpiece cannothave been cut before 1482, two decades after Rogier's death in 1464.Dendrochronology demonstrates that some art-historical opinions mustbe revised: Berlin has the early painting from Rogier van der Weyden'slifetime. New York and Granada have the posthumous copy.
Dating back in time
The oldest TreeBristlecone pine groves are found atelevations up to 11,000 feet (3352m)."Methuselah" was foundto be 4,723 years old andremains today the world'soldest known living tree.Tree-ring dating 7000 years backwards
Chemical MethodsFluorine (FUN) Test: A dating method that measures the amount of fluorine,nitrogen, and uranium in bones. Older bones have more fluorine and uraniumand less nitrogen. But because decomposition happens at different speeds indifferent places, it's not possible to compare bones from different sites.PILTDOWN MANOn December 18,1912Charles Dawson andArthur Smith Woodwardclaimed the discoveryof the remains of anearly human fossil,Eoanthropus dawsoni. It was found in a shallowgravel pit near the village of Piltdown in the Countyof Sussex. It became known as the Sussex Man,and then Piltdown Man, the name that stuck.
The Fluorine TestAnalysis of fluorine content in thejawbones in 1948 indicated muchlower fluorine content than justifiedby claimed age Orangutan jaw
Amino-Acid StructureAmino Acid Dating: The method is based on that certain types of aminoacids exist in two alternative structural forms. Their chemical compositionis identical but the atoms arrangement is reversed in one of the forms. Thetwo forms are called L (laveo-) and D (dextro-) form. In living systems theL-form is synthesized, but after death these L-forms undergo a slow transformation and change to D-form. The process is called racemization. TheExtend of racemization correlates with time and can be used for dating.
Amino-Acid DatingL DdL k L L k D Ddt1 1 D / L t ln 2 k L,D 1 D / L
PaleomagnetismAt the time of their formation, iron-bearing rocks and sediments mayacquire a natural remnant magnetism . This primary magnetismaligns parallel to the existing magnetic field of the Earth. In a sense,a rock becomes a compass capturing its orientation to the Earth'smagnetic field in its structure.Today the orientation of the magnetic field of the Earth is directeddownward in the northern hemisphere and upward in the southernhemisphere. Earth's magnetic field periodically reverses its polarity.During the time of reversed polarity, a compass needle would pointsouth. These reversals make excellent markers in the geologicrecord because they global in extend. The age of these reversalscan be determined by radiometric dating. The age of a fossil can bedetermined by correlating the position of the strata of rock where itwas found and where a reversal occurs.
Stable Isotope 18O/16O ratioStable isotope data derived from mineral and biological materialscan provide a variety of insights into environmental conditions, itIs mostly used in geochronology and correlation. Oxygen isotopes(18O/16O) are widely used in the correlation of Quaternary marinesediments. Oxygen isotope concentrations in mollusk shell andalgal material normalize with seawater while the organisms are alive.During periods of glaciation, large volumes of 16O become trappedin glacial ice, enriching ocean water in the heavier oxygen isotope.Oxygen isotope data extracted from shell-bearing sediments provideinformation about cycles of glaciation (and climate change), and canbe used for relative dating.The oxygen isotopic composition of carbonate hydroxyapatite in teeth andbones reflects the 18O/16O ratio of the water and food that was consumedby the individual, and can be used to tell where they came from.
Archaeological Dating Methods “Everything which has come down to us from heathendom is wrapped in a thick fog; it belongs to a space of time we cannot measure. We know that it is older than Christendom, but whether by a couple of years or a couple of centuries, or even by more than a millennium, we can do no more than guess” Rasmus Nyerup, 1802. The Need for Reliable Dating The
