Archaeology Chapter 6

Absolute Date

A date expressed as a specific unit of scientific measurement, such as days, years, centuries, or millennia; an absolute determination attempting to pinpoint a discrete, known interval in time.

Argon-argon Dating

A high-precision method for estimating the relative quantities of argon-39 to argon-40 gas; used to date volcanic ashes that are between 500,000 and several million years old.

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 (or tree-ring) dating in which old wood has been scavenged and re-used in a later archaeological site; the resulting date is not a true age of the associated human activity.

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 (for instance, ceramic) styles.

Mean Ceramic Date

A statistical technique for combining the median age of manufacture for temporally significant pottery types to estimate the average age of a feature or site.

Thermoluminescence

A trapped charge dating technique used on ceramics and burnt stone artifacts— anything mineral that has been heated to more than 500° C.

Optically Stimulated Luminescense

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.

Relative Dates

Dates expressed relative to one another (for instance, earlier, later, more recent, and so forth) instead of in absolute terms.

What do archaeological dates date?

Dating techniques tell us nothing directly about cultural activities. Radiocarbon dating, for example, tells us when a plant or an animal died—it is up to the archaeologist to relate the event being dated to a behavioral (cultural) event of interest.

What are the major dating techniques of historic sites?

Documentary evidence usually provides dates for historical sites. When such evidence is not available, known ages of particular artifact types are generated to create age range or median ages for historical features or sites using TPQ and mean ceramic age dates.

What is the difference between relative and absolute dating?

Relative dating places sites, strata, features, and artifacts in relative order, without saying how much older or younger one site, stratum, feature, or artifact is than another. Absolute dating provides specific ages or specific age ranges. Absolute dating methods are absolute in the sense that they provide a particular age range at a known level of probability.

Reservoir Effect

Samples from organisms that took in carbon from a source that was depleted of or enriched in 14C relative to the atmosphere may return ages that are considerably older or younger than they actually are

Time-makers

Similar to index fossils in geology; artifact forms that research shows to be diagnostic of a particular period of time.

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.

Half-life

The time required for half of the carbon-14 available in an organic sample to decay; the standard is 5568 years, although it is known that the half-life is closer to 5730 years.

Tree-ring Dating (Dendrochronology)

The use of annual growth rings in trees to assign calendar ages to ancient wood samples.

Radiocarbon Dating

The use of the decay of the radioactive isotope carbon-14 to date organic materials that are up to 45,000 years old.

What are the major dating techniques, what materials do they date, and what is their time range?

Tree-ring dating (dendrochronology) dates wood of particular species; it is limited to relatively small regions and usually cannot date samples that are more than 2000 years old. Radiocarbon dating dates any organic material using the known rate of decay of 14C; it is useful for materials less than 45,000 years old. Trapped charge dating—thermoluminescence (TL), optically stimulated luminescence (OSL), and electron spin resonance (ESR)—date ceramics or burned stone tools, eolian sediments, and tooth enamel, respectively. They date an object by calculating the amount of background radiation the object has been subjected to since the object's electron "clock" was last reset by heat (TL) or sunlight (OSL). These techniques can extend back several hundred thousand years. Argon-argon dates volcanic rock, especially ash. This technique can date volcanic layers that are millions of years old.