Module 3 Flashcards
Relative dating
The ability to determine that X is older than Y, but not determine how old either is.
Absolute dating
The ability to determine an age that employs a number (3000 BP, 200 BC, 100,000 years ago).
Law of superposition
In an undisturbed sequence, layers at the bottom will be older than layers above them.
Stratigraphy
The study of soil and other layers within an archaeological site.
Stratigraphic profile
A map / illustration recording the different layers within an archaeological site.
Seriation
The changes in frequency over time of an artifact or other archaeological phenomenon, from first appearing, to growing in popularity, to eventual demise and falling into disuse.
Seriation is a dating technique used in archaeology to arrange artifacts, fossils, or features in chronological order based on their stylistic or typological similarities and differences. It helps archaeologists understand the relative chronological sequence of items
Battleship curve
A plot of the relative frequency over time of an artifact or other archaeological phenomenon, with each bar centred.
The standard graphical result of seriation is a series of “battleship curves,” which are horizontal bars representing percentages plotted on a vertical axis. Plotting several curves can allow the archaeologist to develop a relative chronology for an entire site or group of sites
Radioactive decay of isotopes
Loss of particular isotopes over time
Three kinds of carbon
Three carbon isotopes, with 12 and 13 being stable and 14 radioactive
Half-life and decay
The amount of time required for a radioactive element to decay to one-half of its original amount.
Radiocarbon half-life (in round numbers)
5,700 years
Half-life and maximum age limit on dating
Radiocarbon’s short half life results in the inability to date anything much older than 30,000-50,000 years old
Photosynthetic pathways and radiocarbon dating
Different types of plants take up radiocarbon at different frequencies; means that plants of the same age will provide different radiocarbon ages
Radiocarbon dating bone
Bone collagen (organic) does not always preserve well; inorganic component (appetite) can be contaminated with radiocarbon from other sources
Reservoir effect
Stored amounts of older radiocarbon can make more recent specimens date far older than they actually are
Upwelling
Process of bringing deep ocean water to the surface, which caries old radiocarbon; results in dates that are far older than the organism actually is.
Calibration
Correcting for known fluctuations in atmospheric levels of radiocarbon by dating known-age items such as tree rings.
Statistical estimate
Radiocarbon levels estimated by measuring decay over a short period of time, resulting in the possibility of error
AMS dating
Accelerator Mass Spectrometry dating – directly measures amount of radiocarbon left in an organic object
Dendrochronology
Tree ring datin
Cross dating
Creating a tree ring dating sequence
Old wood
Constructions employing old wood specimens as building materials, potentially throwing dendrochronology dates off by hundreds of years
Potassium-argon
Dating volcanic sediments by comparing ratios of radioactive potassium 40 to argon 39.
Potassium-argon dating range
Minimal date approximately 500,000 years ago to several billion years ago
Uranium series dating
Dates determined by comparing ratios of uranium and thorium or two different uranium isotopes
Fission track dating
Dates based on spontaneous fission of Uranium 238 in glass-like materials
Obsidian hydration
Measuring water absorption rind of fractured obsidian to determine time elapsed since fracture occurred
Trapped-charge dating
Determines when something was last exposed to light or heat, depending on method
Thermoluminescence
Variety of trapped-charge dating based on last exposure to particular temperature; calculated based on amount of light emitted during reheating
Reversals of magnetic poles
North and south poles occasionally reverse
Movement of magnetic North
Changes in position of earth’s magnetic poles over time
Paleomagnetic dating
Measuring age based on known position of earth’s magnetic poles, measured by looking at alignment of iron in soil
Chronology
The measurement and study of time and constructing time sequences
Accuracy
Ability to produce a correct answer
Precision
Fineness of resolution
Accuracy versus precision
Correct answer versus fine resolution; ideally both are present
Reliability
Ability to produce same result repeatedly
Validity
Are you measuring what you think you are measuring?
