Ch. 5 - Chronology Building: How To Get A Date Flashcards
Absolute date
A date expressed in specific units of scientific measurement, such as days, years, centuries, or millennia; absolute determinations attempting to pinpoint a discrete, known interval in time.
Relative dates
Dates expressed relative to one another (for instance, earlier, later, more recent) instead of in absolute terms.
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.
Law of superposition
The geologic principle that 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.
Time markers
Artifact forms that, as with index fossils in geology, research shows to be diagnostic of a particular period of time.
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.
Tree-ring dating
(Dendrochronology)
The use of annual growth rings in trees to assign calendar ages to ancient wood samples.
Half-life (of 14C)
The time required for half of the carbon-14 available in an organic sample to decay.
5730 years.
Photosynthetic pathways
The specific chemical processes through which plants metabolize carbon. Because the three major pathways discriminate against carbon-13 in different ways, similarly aged plants that use different pathways can produce different radiocarbon ages.
Reservoir effect
When organisms take in carbon from a source that is depleted of or enriched in carbon-14 to the relative atmosphere; carbon dating of such samples may return ages that are considerably older or younger than they actually are.
de Vries effects
Fluctuations in the radiocarbon-dating calibration curve produced by variations in the atmosphere’s carbon-14 content; these can cause radiocarbon dates to calibrate to more than one calendar age.
Accelerator Mass Spectrometry (AMS)
A method of radiocarbon dating that counts the proportion of carbon isotopes directly (rather that using the Geiger counter method), thereby dramatically reducing the quantity of database material required.
Trapped charge dating
Forms of dating that rely upon 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.
Dosimeter
A device to measure the amount of gamma radiation emitted by sediments. It is normally buried in a stratum for a year to record the annual dose of radiation. Often a short length of pure copper tubing filled with calcium sulfate.
ThermoLuminescence (TL)
A trapped charge dating technology used on ceramics and burnt stone artifacts – anything mineral that has been heated to more than 500 degrees C.
Neanderthals
An early form of Humans who lived in Europe and the Near East about 300,000 to 30,000 years ago. Biological anthropologists debate whether Neanderthals were in the direct evolutionary line leading to Homo sapiens.
Optically Stimulated Luminescence (OSL)
A trapped charge dating technique used to date sediments; it measures the time elapsed between the last time a few moments’ exposure to sunlight reset the clock to zero and the present.
Electron Spin Resonance (ESR)
A trapped charge technique used to date tooth enamel and burnt stone tools; it can date teeth that are beyond the range of radiocarbon dating.
Homo erectus
A hominin who lived in Africa, Asia, and Europe between 2 million and 500,000 years ago. These hominins walked upright, made simple stone tools and may have used fire.
Argon-argon dating
A high-precision method for estimating the relative quantities of argon-39 and argon-40 gas; used to date volcanic ashes that are between 500,000 and several million years old.
Old wood problem
A potential problem with radiocarbon (or 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.
