Absolute dating

Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy.[1][2] Absolute dating provides a numerical age or range in contrast with relative dating which places events in order without any measure of the age between events.

In archaeology, absolute dating is usually based on the physical, chemical, and life properties of the materials of artifacts, buildings, or other items that have been modified by humans and by historical associations with materials with known dates (coins and written history). Techniques include tree rings in timbers, radiocarbon dating of wood or bones, and trapped-charge dating methods such as thermoluminescence dating of glazed ceramics.[3] Coins found in excavations may have their production date written on them, or there may be written records describing the coin and when it was used, allowing the site to be associated with a particular calendar year.

In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young (radiocarbon dating with 14
C
) to systems such as uranium–lead dating that allow acquisition of absolute ages for some of the oldest rocks on earth.

Radiometric techniques

Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes. Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age. For example, techniques based on isotopes with half lives in the thousands of years, such as carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments.

Radiocarbon dating

One of the most widely used and well-known absolute dating techniques is carbon-14 (or radiocarbon) dating, which is used to date organic remains. This is a radiometric technique since it is based on radioactive decay. Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide. Carbon-14 moves up the food chain as animals eat plants and as predators eat other animals. With death, the uptake of carbon-14 stops.

It takes 5,730 years for half the carbon-14 to change to nitrogen; this is the half-life of carbon-14. After another 5,730 years only one-quarter of the original carbon-14 will remain. After yet another 5,730 years only one-eighth will be left.

By measuring the carbon-14 in organic material, scientists can determine the date of death of the organic matter in an artifact or ecofact.

Limitations

The relatively short half-life of carbon-14, 5,730 years, makes dating reliable only up to about 50,000 years. The technique often cannot pinpoint the date of an archeological site better than historic records, but is highly effective for precise dates when calibrated with other dating techniques such as tree-ring dating.

An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem. It is possible, particularly in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record. Thus dating that particular tree does not necessarily indicate when the fire burned or the structure was built.

For this reason, many archaeologists prefer to use samples from short-lived plants for radiocarbon dating. The development of accelerator mass spectrometry (AMS) dating, which allows a date to be obtained from a very small sample, has been very useful in this regard.

Potassium-argon dating

Other radiometric dating techniques are available for earlier periods. One of the most widely used is potassium–argon dating (K–Ar dating). Potassium-40 is a radioactive isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated. Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.

Argon, a noble gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay. The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice. K–Ar dating was used to calibrate the geomagnetic polarity time scale.

Luminescence dating

Thermoluminescence

Thermoluminescence testing also dates items to the last time they were heated. This technique is based on the principle that all objects absorb radiation from the environment. This process frees electrons within minerals that remain caught within the item.

Heating an item to 500 degrees Celsius or higher releases the trapped electrons, producing light. This light can be measured to determine the last time the item was heated.

Radiation levels do not remain constant over time. Fluctuating levels can skew results – for example, if an item went through several high radiation eras, thermoluminescence will return an older date for the item. Many factors can spoil the sample before testing as well, exposing the sample to heat or direct light may cause some of the electrons to dissipate, causing the item to date younger.

Because of these and other factors, Thermoluminescence is at the most about 15% accurate. It cannot be used to accurately date a site on its own. However, it can be used to confirm the antiquity of an item.

Optically stimulated luminescence (OSL)

Optically stimulated luminescence (OSL) dating constrains the time at which sediment was last exposed to light. During sediment transport, exposure to sunlight 'zeros' the luminescence signal. Upon burial, the sediment accumulates a luminescence signal as natural ambient radiation gradually ionises the mineral grains.

Careful sampling under dark conditions allows the sediment to be exposed to artificial light in the laboratory which releases the OSL signal. The amount of luminescence released is used to calculate the equivalent dose (De) that the sediment has acquired since deposition, which can be used in combination with the dose rate (Dr) to calculate the age.

Dendrochronology

Tree.ring.arp
The growth rings of a tree at Bristol Zoo, England. Each ring represents one year; the outside rings, near the bark, are the youngest.

Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree rings, also known as growth rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year.

Dendrochronology has three main areas of application: paleoecology, where it is used to determine certain aspects of past ecologies (most prominently climate); archaeology, where it is used to date old buildings, etc.; and radiocarbon dating, where it is used to calibrate radiocarbon ages (see below).

In some areas of the world, it is possible to date wood back a few thousand years, or even many thousands. Currently, the maximum for fully anchored chronologies is a little over 11,000 years from present.[4]

Amino acid dating

Amino acid dating is a dating technique [5][6][7][8][9] used to estimate the age of a specimen in paleobiology, archaeology, forensic science, taphonomy, sedimentary geology and other fields. This technique relates changes in amino acid molecules to the time elapsed since they were formed. All biological tissues contain amino acids. All amino acids except glycine (the simplest one) are optically active, having an asymmetric carbon atom. This means that the amino acid can have two different configurations, "D" or "L" which are mirror images of each other.

With a few important exceptions, living organisms keep all their amino acids in the "L" configuration. When an organism dies, control over the configuration of the amino acids ceases, and the ratio of D to L moves from a value near 0 towards an equilibrium value near 1, a process called racemization. Thus, measuring the ratio of D to L in a sample enables one to estimate how long ago the specimen died.[10]

See also

References

  1. ^ Evans, Susan Toby; David L., Webster, eds. (2001). Archaeology of ancient Mexico and Central America : an encyclopedia. New York [u.a.]: Garland. p. 203. ISBN 9780815308874.
  2. ^ Henke, Winfried (2007). Handbook of paleoanthropology. New York: Springer. p. 312. ISBN 9783540324744.
  3. ^ Kelly, Robert L.; Thomas, David Hurst (2012). Archaeology: Down to Earth (Fifth edition. ed.). ISBN 9781133608646.
  4. ^ McGovern PJ; et al. (1995). "Science in Archaeology: A Review". American Journal of Archaeology. 99 (1): 79–142.
  5. ^ Bada, J. L. (1985). "Amino Acid Racemization Dating of Fossil Bones". Annual Review of Earth and Planetary Sciences. 13: 241–268. Bibcode:1985AREPS..13..241B. doi:10.1146/annurev.ea.13.050185.001325.
  6. ^ Canoira, L.; García-Martínez, M. J.; Llamas, J. F.; Ortíz, J. E.; Torres, T. D. (2003). "Kinetics of amino acid racemization (epimerization) in the dentine of fossil and modern bear teeth". International Journal of Chemical Kinetics. 35 (11): 576. doi:10.1002/kin.10153.
  7. ^ Bada, J.; McDonald, G. D. (1995). "Amino Acid Racemization on Mars: Implications for the Preservation of Biomolecules from an Extinct Martian Biota" (PDF). Icarus. 114: 139–143. Bibcode:1995Icar..114..139B. doi:10.1006/icar.1995.1049. PMID 11539479.
  8. ^ Johnson, B. J.; Miller, G. H. (1997). "Archaeological Applications of Amino Acid Racemization". Archaeometry. 39 (2): 265. doi:10.1111/j.1475-4754.1997.tb00806.x.
  9. ^ 2008 [1] quote: The results provide a compelling case for applicability of amino acid racemization methods as a tool for evaluating changes in depositional dynamics, sedimentation rates, time-averaging, temporal resolution of the fossil record, and taphonomic overprints across sequence stratigraphic cycles.
  10. ^ Amino Acid Geochronology Laboratory, Northern Arizona University

Further reading

  • Chronometric dating in archaeology, edited by R.E. Taylor and Martin J. Aitken. New York: Plenum Press (in cooperation with the Society for Archaeological Sciences). 1997.
Chronological dating

Chronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously established chronology. This usually requires what is commonly known as a "dating method". Several dating methods exist, depending on different criteria and techniques, and some very well known examples of disciplines using such techniques are, for example, history, archaeology, geology, paleontology, astronomy and even forensic science, since in the latter it is sometimes necessary to investigate the moment in the past in which the death of a cadaver occurred.

Circa

Circa (from Latin, meaning 'around, about, roughly, approximately') – frequently abbreviated c., ca., or ca and less frequently circ. or cca. – signifies "approximately" in several European languages and as a loanword in English, usually in reference to a date. Circa is widely used in historical writing when the dates of events are not accurately known.

When used in date ranges, circa is applied before each approximate date, while dates without circa immediately preceding them are generally assumed to be known with certainty.

Examples:

1732–1799: Both years are known precisely.

c. 1732 – 1799: The beginning year is approximate; the end year is known precisely.

1732 – c. 1799: The beginning year is known precisely ; the end year is approximate.

c. 1732 – c. 1799: Both years are approximate.

Dating (disambiguation)

Dating is an activity by two humans who are exploring or are in a romantic relationship.

The term may also refer to:

Courtship, period in a couple's relationship which precedes engagement and marriage

Timestamp, information identifying the date and time when a certain event occurredChronological dating, estimating the age of an object or linguistic artifact

Relative dating, determining the relative order of past events

Absolute dating, determining an approximate age in archaeology or geology

Radiometric dating, a family of techniques used to date objects using radioactive impurities

Dendrochronology, dating tree rings to the year they were formed

Ediacaran

The Ediacaran Period ( ), spans 94 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 541 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.

The Ediacaran Period's status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years.

Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacara biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at 31°19′53.8″S 138°38′0.1″E.

Era (geology)

A geologic era is a subdivision of geologic time that divides an eon into smaller units of time. The Phanerozoic Eon is divided into three such time frames: the Paleozoic, Mesozoic, and Cenozoic (meaning "old life", "middle life" and "recent life") that represent the major stages in the macroscopic fossil record. These eras are separated by catastrophic extinction boundaries, the P-T boundary between the Paleozoic and the Mesozoic and the K-Pg boundary between the Mesozoic and the Cenozoic. There is evidence that catastrophic meteorite impacts played a role in demarcating the differences between the eras.

The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. This covered the four billion years of Earth history prior to the appearance of hard-shelled animals. More recently, however, the Archean and Proterozoic eons have been subdivided into eras of their own.

Geologic eras are further subdivided into geologic periods, although the Archean eras have yet to be subdivided in this way.

Floruit

Floruit (UK: , US: ), abbreviated fl. (or occasionally flor.), Latin for "he/she flourished", denotes a date or period during which a person was known to have been alive or active. In English, the word may also be used as a noun indicating the time when someone flourished.

Geological period

A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place.

These periods form elements of a hierarchy of divisions into which geologists have split the Earth's history.

Eons and eras are larger subdivisions than periods while periods themselves may be divided into epochs and ages.

The rocks formed during a period belong to a stratigraphic unit called a system.

Glossary of archaeology

This page is a glossary of archaeology, the study of the human past from material remains.

Gojko Barjamovic

Gojko Johansen Barjamovic is Senior Lecturer on Assyriology at Harvard University. He is a specialist in the political and social history of Assyria in the 2nd and 1st millennia BC, and particularly trade and the development of early markets. He has also worked on absolute dating and the chronology of the Ancient Near East. He was a member of the team that used statistical methods to interrogate the records of ancient merchants found at Kültepe/Kanesh near the modern Turkish city of Kayseri to locate the probable location of ancient cities.

Morphology (archaeology)

Morphology in archaeology, the study of shapes and forms, and their grouping into period styles remains a crucial tool, despite modern techniques like radiocarbon dating, in the identification and dating not only of works of art but all classes of archaeological artefact, including purely functional ones (ignoring the question of whether purely functional artefacts exist). The term morphology ("study of shapes", from the Greek) is more often used for this. Morphological analyses of many individual artefacts are used to construct typologies for different types of artefact, and by the technique of seriation a relative dating based on shape and style for a site or group of sites is achieved where scientific absolute dating techniques cannot be used, in particular where only stone, ceramic or metal artefacts or remains are available, which is often the case. That artefacts such as pottery very often survive only in fragments makes precise knowledge of morphology even more necessary, as it is often necessary to identify and date a piece of pottery from only a few sherds.

In contrast to recent trends in academic art history, the succession of schools of archaeological theory in the last century, from culture-historical archaeology to processual archaeology and finally the rise of post-processual archaeology in recent decades has if anything increased the importance of the study of style in archaeology.

Nemegt Formation

The Nemegt Formation (or Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. It overlies and sometimes interfingers with the Barun Goyot Formation. Interfingering has been noted at the stratotype (Red Walls) and Khermeen Tsav. It consists of river channel sediments and contains fossils of fish, turtles, crocodilians, and a diverse fauna of dinosaurs, including birds. The climate associated with it was wetter than when preceding formations were deposited; there seems to have existed at least some degree of forest cover. Fossilized trunks have been also found.

There has been no absolute dating of the Nemegt Formation. It is, however, almost certainly early Maastrichtian c 71-70 Ma. Gradzinski and others considered a Campanian age possible but more recent research indicates otherwise. A Campanian age no longer seems credible, because the Alagteegian (or lower Djadokhtan, at the locality "Chuluut Uul") has been radiometrically dated at about 73.5 Ma or even younger (a more recent K/Ar date is 71.6 +/- 1.6 Ma). The c 73.5 (or perhaps 72) Ma Alagteegian is separated from the Nemegt by the "classic" Djadokhtan (e.g. Bayan Dzag), later Djadohktan (represented by Ukhaa Tolgod) and Barungoyotian (Khulsan). All these intervening horizons almost certainly represent more than the 1.5 million years between the dated Alagteegian level and the onset of Maastrichtian time (72.1 million Ma according to current dating). Ergo the Nemegt is entirely Maastrichtian. See also Shuvalov, Sochava and Martinsson The Age of Dinosaurs in Russia and Mongolia. The presence of Saurolophus further supports an early Maastrichtian age as the same genus occurs in the early Maastrichtian Horseshoe Canyon formation.

OCR

OCR may refer to:

Offices of Civil Rights, common sub-agency or sub-component name of U.S. federal agencies:

State Office of Civil Rights, U.S. Department of State

GSA Office of Civil Rights, General Services Administration

ED Office for Civil Rights, U.S. Department of Education

HHS Office for Civil Rights, U.S. Department of Health and Human Services

DOJ Office for Civil Rights, Office of Justice Programs (OJP)

Official Cash Rate, the interest rate paid by banks in the overnight money market

Oil Circuit Recloser, an oil-filled type of recloser.

Oil Control Ring, Piston ring

Optical character recognition, conversion of images of text into characters.

The OCR-A font, designed to simplify character recognition

The similar OCR-B font

Optimum currency region, a theoretical optimal area where one currency would make most benefit

Organically moderated and cooled reactor, a type of nuclear reactor

Otago Central Railway, now a heritage railway in Otago, New Zealand.

Ottawa Central Railway a Canadian Shortline owned by CN Rail

Over consolidation ratio, a consolidation measurement in geotechnical engineering

OverClocked ReMix, an organization and website dedicated to preserving and paying tribute to video game music through re-orchestration and reinterpretation

Oxford, Cambridge and RSA Examinations, a UK-based exam board

Oxidizable carbon ratio dating, a method of absolute dating

Transvaginal oocyte retrieval, a technique used in vitro fertilization

Obstacle course racing

Obsidian hydration dating

Obsidian hydration dating (OHD) is a geochemical method of determining age in either absolute or relative terms of an artifact made of obsidian.

Obsidian is a volcanic glass that was used by prehistoric people as a raw material in the manufacture of stone tools such as projectile points, knives, or other cutting tools through knapping, or breaking off pieces in a controlled manner, such as pressure flaking.

Obsidian obeys the property of mineral hydration, and absorbs water, when exposed to air, at well defined rate. When an unworked nodule of obsidian is initially fractured, there is typically less than 1% water present. Over time, water slowly diffuses into the artifact forming a narrow "band," "rim," or "rind" that can be seen and measured with many different techniques such as a high-power microscope with 40-80 power magnification, depth profiling with SIMS (secondary ion mass spectrometry), and IR-PAS (infra red photoacoustic spectroscopy). In order to use obsidian hydration for absolute dating, the conditions that the sample has been exposed to and its origin must be understood or compared to samples of a known age (e.g. as a result of radiocarbon dating of associated materials).

Pastonian Stage

The Pastonian interglacial, now called the Pastonian Stage (from Paston, Norfolk), is the name for an early or middle Pleistocene stage used in the British Isles. It precedes the Beestonian Stage and follows the Pre-Pastonian Stage. Unfortunately the precise age of this stage cannot yet be defined in terms of absolute dating or MIS stages. The Pre-Pastonian Stage is equivalent to the Tiglian C5-6 Stage of Europe and the Pre-Illinoian I glaciation of the early Pre-Illinoian Stage of North America.Deciduous woodland, increased including species such as Hornbeam (Carpinus), Elm (Ulmus), Hazel (Corylus), and Spruce (Picea). Towards the end of the period, there is evidence for a fall in sea levels and an increase in grassland species.

Relative dating

Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e. estimated age). In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating in the early 20th century, which provided a means of absolute dating, archaeologists and geologists used relative dating to determine ages of materials. Though relative dating can only determine the sequential order in which a series of events occurred, not when they occurred, it remains a useful technique. Relative dating by biostratigraphy is the preferred method in paleontology and is, in some respects, more accurate. The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of 'relative dating' as observed in geology from the 17th century to the early 20th century.

Sahand

Sahand (Persian: سهند‎), is a massive, heavily eroded stratovolcano in East Azerbaijan Province, northwestern Iran. At 3,707 m (12,162 ft), it is the highest mountain in the province of East Azarbaijan.

It is one of the highest mountains in Iranian Azerbaijan, in addition to being an important dormant volcano in the country. The Sahand mountains are directly south of Tabriz, the highest peak of which is Kamal at an elevation of 3,707 m.. Approximately 17 peaks can be accounted for as being over 3,000 m. in height. Due to the presence of a variety of flora and fauna, the Sahand mountains are known as the bride of mountains in Iran.The absolute dating of Sahand rocks indicates that this volcano has been sporadically active from 12 million years ago up to almost 0.14 million years ago. Sahand is made chiefly of dacite and associated felsic rocks.

Seriation (archaeology)

In archaeology, seriation is a relative dating method in which assemblages or artifacts from numerous sites, in the same culture, are placed in chronological order. Where absolute dating methods, such as carbon dating, cannot be applied, archaeologists have to use relative dating methods to date archaeological finds and features. Seriation is a standard method of dating in archaeology. It can be used to date stone tools, pottery fragments, and other artifacts. In Europe, it has been used frequently to reconstruct the chronological sequence of graves in a cemetery (e.g. Jørgensen 1992; Müssemeier, Nieveler et al. 2003).

Speleothem

Speleothems ( ; Ancient Greek: "cave deposit"), commonly known as cave formations, are secondary mineral deposits formed in a cave. Speleothems typically form in limestone or dolomite solutional caves. The term "speleothem" as first introduced by Moore (1952), is derived from the Greek words spēlaion "cave" + théma "deposit". The definition of "speleothem" in most publications, specifically excludes secondary mineral deposits in mines, tunnels and on man-made structures. Hill and Forti more concisely defined "secondary minerals" which create speleothems in caves as;

A "secondary" mineral is one which is derived by a physicochemical reaction from a primary mineral in bedrock or detritus, and/or deposited because of a unique set of conditions in a cave; i.e., the cave environment has influenced the mineral's deposition.

Yoshinogari site

Yoshinogari (吉野ヶ里 遺跡 Yoshinogari iseki) is the name of a large and complex Yayoi archaeological site in Yoshinogari and Kanzaki in Saga Prefecture, Kyūshū, Japan. According to the Yayoi chronology established by pottery seriations in the 20th century, Yoshinogari dates to between the 3rd century BC and the 3rd century AD. However, recent attempts to use absolute dating methods such as AMS radiocarbon dating have shown that the earliest Yayoi component of Yoshinogari dates to before 400 BC.

This archaeological site is of great importance in Japanese and world prehistory because of the massive size and important nature of the settlement and the artifacts found there. Yoshinogari consists of a settlement, a cemetery, and multiple ditch-and-palisade enclosed precincts. Bronze mirrors from China, Japanese-style bronze mirrors, bronze daggers, coins, bells, and halberds, iron tools, wooden tools, prehistoric human hair, and many other precious artifacts have been unearthed from Yoshinogari features. The total area of this site is approximately 40 hectares. This site has been continuously excavated by a number of different agencies and institutions since 1986. Due to the superior features, artifacts, and significance in Japanese prehistory and protohistory, the site was designated as a "Special National Historic Site" in 1991, and a National Park was created there in 1992. Ancient structures are being reconstructed on the site and the park is a major tourist attraction.

Yoshinogari is located 12 km from the Ariake Sea on a low hill that extends out of the Sefuri Mountains and is surrounded on three sides by land that is suitable for wet-rice (paddy) cultivation.

Key topics
Calendars
Astronomic time
Geologic time
Chronological
dating
Genetic methods
Linguistic methods
Related topics
Overviews
History of geology
Сomposition and structure
Historical geology
Motion
Water
Geophysics
Applications
Occupations

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.