Archaeology Ch. 5 & 6
behavioral processes
1.Acquisition 2.Manufacture 3.Use 4.Deposition All forms of archaeological data, individually and collectively, are used to reconstruct the stages of ancient behavior.
Carbon 14 and Radiometric decay (absolute darting)
: a measure of the rate at which certain radioactive isotopes disintegrate •e.g.) AMS (accelerator mass spectrometry) •Trapped charge dating •Argon-Argon
Absolute date
A date expressed as specific units of scientific measurement, such as days, years, centuries, or millennia; absolute determinations attempting to pinpoint a discrete, known interval of time.
Thermoluminescence
A trapped charge dating technique used on ceramics and burned stone artifacts. • Anything mineral that has been heated to more than 500° C. •Measures light released when electrons move back into orbit •Produces mean date with standard deviation
Electron spin resonance (ESR)
A trapped charge dating technique used to date tooth enamel and burned stone tools; •It can date teeth that are beyond the range of radiocarbon dating. •Used to date tooth enamel - not sensitive to light •Use electromagnetic radiation to reset the electrons. •Helpful in understanding the evolutionary pathways of our earliest hominid ancestors.
Argon-argon dating
High-precision method for estimating the relative quantities of argon-39 to argon-40 gas; •Used to date volcanic ashes between 500,000 and several million years old. •Tracks radioactive decay and half-lives •Not as precise as radiocarbon dating •Useful in dating the age of the formation of a particular rock layer •Useful only for dating materials that are hundreds of thousands or millions of years old •Helpful in places where early human remains are found (e.g. Africa)
Law of Superposition
In any pile of sedimentary rocks that have not been disturbed by folding or overturning, each bed is older than the layers above and younger than the layers below; also known as Steno's Law
dosimeter
a device to measure the amount of gamma radiation emitted by sediments. •Records how much radiation it was exposed to in a year's time. •Electrons are returned to their orbits by heat (500° C) or sunlight - resets the clock to zero
Accelerator mass spectrometry (AMS)
a method of radiocarbon dating that counts the proportion of carbon isotopes directly (rather than using the indirect Geiger counter method), thereby dramatically reducing the quantity of datable material required.
Old wood problem
a potential problem with radiocarbon (tree-ring) dating in which old wood has been scavenged and reused in a later archaeological site; •The resulting date is not a true age of the associated human activity. •e.g.) the dating of the pyramids at Giza
Stratigraphy
a site's physical structure produced by the deposition of geological and/or cultural sediments into layers, or strata, to reveal age and original inhabitants. •Strata can be in-tact with clear delineations, but not always. •Human and natural processes churn the sediments, moving things up or down. •Most modern archaeological sites are complex.
Optically stimulated luminescence
a trapped charge dating technique used to date sediments; •The age is the time elapsed between the last time a few moments exposure to sunlight reset the clock to zero and the present. •Can date dirt - makes this technique very functional •Dates the time when the sands were buried •Can't be exposed to light before testing - issues with contamination •e.g.) Jinmium Rockshelter in Australia •Measures light from the electrons elicited by light of a particular wavelength
Secondary context
alterations of provenience and association by transformational processes cause by either human or natural activity.
Primary context:
conditions in which both provenience and matrix have remained undisturbed since the original deposition.
Relative date
dates expressed relative to one another(for instance, earlier, later, more recent) instead of in absolute terms.
Trapped charge dating
forms of dating that rely on the fact that electrons become trapped in minerals' crystal lattices as a function of background radiation. •The age of the specimen is the total radiation received divided by the annual dose of radiation. •Can go back at least 300,000 years •Includes: 1.Thermoluminescence 2.Optically stimulated luminnescence 3.Electron spin resonance
systemic context
is a living behavioral system wherein artifacts are part of the ongoing system of manufacture, use, reuse, and discard.
hominins
members of the evolutionary line that contains humans and our early bipedal ancestors.
Dendrochronology (absolute dating)
method based on the study and comparison of patterns of tree-ring growth the use of annual growth rings in trees to assign calendar ages to ancient wood samples
Sedimentary rock
rock formed when the weathered products of preexisting rocks have been transported by and deposited in water and are turned once again to stone.
Reservoir effect:
samples from organisms that took in carbon from a source that was depleted of or enriched in carbon-14 relative to the atmosphere may return ages that are considerably older or younger than they actually are.
The index fossil concept
the idea that strata containing similar fossil assemblages are of similar age. •This concept enables archaeologists to characterize and date strata within sites using distinctive artifact forms that research shows to be diagnostic of a particular period of time. •Allowed geologists to make the first geological maps. •Allows archaeologists to to date sites relative to one another.
Half-life:
the time required for half of the carbon-14 available in an organic sample to decay; •Originally set at 5568 years, it was later changed to 5730 years (one half-life). •Only good for organic remains that are younger than about 45,000 years. •Radiocarbon dates carry standard deviations (+ 70 years, for example) - see slide 11 for more info
archaeological context
where they can continue to be affected by human action, but where they also are affected by natural processes.
Radiocarbon Dating, How it Works, continued
•14C oxidizes and forms carbon dioxide, which is dispersed throughout the atmosphere by stratospheric winds. •About 98 percent of all 14C enters the oceans; plants take up the rest through photosynthesis. •From plants, it enters herbivores, and then carnivores. All organic life contains radioactive carbon. •As long as an organism is alive, the amount of 14C in it remains in equilibrium with the atmosphere. •Once the organism dies, the amount of 14C in its body begins to decrease.
Nicolaus Steno
•Became the foundation of all stratigraphic interpretation. •Steno presented important ideas on the formation of strata and fossils •Fossils came to be inside solid rock because the rock was once liquid •Means the fossils were older than the rock (already there)
Tree-Ring Dating, Tree Rings and Climate
•Because tree-ring width is controlled by precipitation as well as temperature, trees preserve a record of past environmental conditions. •Detailed climatic reconstructions provide archaeologists with fine-grained paleoenvironmental chronologies (with an appropriate dendrochronological sequence available)
Fossil Footprints at Laetoli: How Old Are the Footprints?
•Leakey surmised that the age of the footprints at Laetoli was more than a million years older than the oldest known tool use. •Used potassium-argon dating on samples from the major stratified layers recognized in the Laetoli area. •The fossil hominid footprints are between 3.49 and 3.56 million years old. •With the dating of the Laetolil footprints, Leakey showed that humans were bipedal long before they made stone tools.
How Old Are The Pyramids
•Some say the pyramids are much older than the 3rd millennium BCE (10,000 BP) •1984/5, radiocarbon dating completed on the pyramid (tested the mortar for carbon using AMS) •Discovered Old Kingdom pyramids were 100 to 400 years older than the documentary dates suggested (Middle Kingdom pyramids matched previous dates) - why? •Old wood problem - needed extensive wood for the pyramid construction, raided older settlements and looted their predecessors' temples and tombs for wood
Relative Dating - the Basics
•Stratigraphy •sequential layering of deposits •Typological Dating •dating human cultural artifacts by tracking changes in stylistic features •Seriation Dating •dating groups of artifacts and sites •Fluorine Analysis •measurement and comparison of amounts of fluorine absorbed by bones from groundwater
Fossil Footprints at Laetoli: Geological Background
•The ash buried the footprints rapidly, soon after they were formed. •Lack of evidence of grasses suggests eruptions took place during dry season. •Raindrop impressions occur along with footprints and widespread erosion, suggesting rainy season downpours.
Seriation
•a relative dating method that orders artifacts based on the assumption that one cultural style slowly replaces an earlier style over time; •With a master seriation diagram, sites can be dated based on their frequency of several artifact (e.g. ceramic) styles.
Fluorine Analysis
•measurement and comparison of amounts of fluorine absorbed by bones from groundwater. •Items such as bone that are in the soil will absorb fluoride from the groundwater over time.
Photosynthetic pathways
•the specific chemical process through which plants metabolize carbon. •The three major pathways discriminate against carbon-13 in different ways; therefore, similarly aged plants that use different pathways can produce different radiocarbon ages. •Different plants have different pathways •Affects dating, but labs attempt to work around this issue (need to know plant variety
