Wikipedia absolute dating

The development of radiocarbon dating has had a profound impact on archaeology.In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances.

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Trees usually add growth rings on a yearly basis, with the spacing of rings being wider in high growth years and narrower in low growth years.

Patterns in tree-ring growth can be used to establish the age of old wood samples, and also give some hints to local climatic conditions.

The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists.

Libby received the Nobel Prize in Chemistry for his work in 1960.

These changes provide a long-term sequence of climatic events, recorded as changes in the thickness of sediment layers (known as "varve analysis"—the term "varve" means a layer or layers of sediment.

Typically, varve refers to lake or glacial sediment), as temperature induced changes in the isotopic ratios for oxygen isotopes in sediments, and in the relative abundance of fossils.

Libby and James Arnold proceeded to test the radiocarbon dating theory by analyzing samples with known ages.

For example, two samples taken from the tombs of two Egyptian kings, Zoser and Sneferu, independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years. Carbon dioxide produced in this way diffuses in the atmosphere, is dissolved in the ocean, and is taken up by plants via photosynthesis.

Animals eat the plants, and ultimately the radiocarbon is distributed throughout the biosphere.

The ratio of λ is a constant that depends on the particular isotope; for a given isotope it is equal to the reciprocal of the mean-life – i.e.

the average or expected time a given atom will survive before undergoing radioactive decay. The calculations involve several steps and include an intermediate value called the "radiocarbon age", which is the age in "radiocarbon years" of the sample: an age quoted in radiocarbon years means that no calibration curve has been used − the calculations for radiocarbon years assume that the , which for more than a decade after Libby's initial work was thought to be 5,568 years.

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