Stratigraphy (archaeology) - Wikipedia
Stratigraphy covers all aspects of sedimentary rocks, particularly from the perspective of their age and regional relationships as well as the correlation of sedimentary rocks in one region with sedimentary rock sequences elsewhere. For further information about these fields, see geologic sciences.
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Such time determinations are made and the record of past geologic events is deciphered by studying the distribution and succession of rock strata, as well as the character of the fossil organisms preserved within the strata. More About Stratigraphy 16 references found in Britannica articles Assorted References field of study In sedimentary rock major references In Earth sciences: Paleontology and stratigraphy In geology: Establishing Tertiary boundaries In Tertiary Period: Major subdivisions of the Tertiary System use in archaeology In archaeology: First steps to archaeology View More.
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Stratigraphy (archaeology)
Thank you for your feedback. Cultural seriations are based on typologies, in which artifacts that are numerous across a wide variety of sites and over time, like pottery or stone tools. If archaeologists know how pottery styles, glazes, and techniques have changed over time they can date sites based on the ratio of different kinds of pottery. This also works with stone tools which are found abundantly at different sites and across long periods of time.
Stratigraphic dating is based on the principle of depositional superposition of layers of sediments called strata. This principle presumes that the oldest layer of a stratigraphic sequence will be on the bottom and the most recent, or youngest, will be on the top. The earliest-known hominids in East Africa are often found in very specific stratigraphic contexts that have implications for their relative dating. These strata are often most visible in canyons or gorges which are good sites to find and identify fossils.
Dating Techniques In Archaeology
Understanding the geologic history of an area and the different strata is important to interpreting and understanding archaeological findings. The majority of chronometric dating methods are radiometric, which means they involve measuring the radioactive decay of a certain chemical isotope.
They are called chronometric because they allow one to make a very accurate scientific estimate of the date of an object as expressed in years. They do not, however, give "absolute" dates because they merely provide a statistical probability that a given date falls within a certain range of age expressed in years. Chronometric methods include radiocarbon, potassium-argon, fission-track, and thermoluminescence.
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The most commonly used chronometic method is radiocarbon analysis. It measures the decay of radioactive carbon 14C that has been absorbed from the atmosphere by a plant or animal prior to its death. Once the organism dies, the Carbon begins to decay at an extremely predictable rate. Radioactive carbon has a half-life of approximately 5, years which means that every 5, years, half of the carbon will have decayed. This number is usually written as a range, with plus or minus 40 years 1 standard deviation of error and the theoretical absolute limit of this method is 80, years ago, although the practical limit is close to 50, years ago.
Because the pool of radioactive carbon in the atmosphere a result of bombardment of nitrogen by neutrons from cosmic radiation has not been constant through time, calibration curves based on dendrochronology tree ring dating and glacial ice cores, are now used to adjust radiocarbon years to calendrical years.
The development of Atomic Absorption Mass Spectrometry in recent years, a technique that allows one to count the individual atoms of 14C remaining in a sample instead of measuring the radioactive decay of the 14C, has considerably broadened the applicability of radiocarbon dating because it is now possible to date much smaller samples, as small as a grain of rice, for example. Dendrochronology is another archaeological dating technique in which tree rings are used to date pieces of wood to the exact year in which they were cut down.
In areas in which scientists have tree rings sequences that reach back thousands of years, they can examine the patterns of rings in the wood and determine when the wood was cut down.