Incremental dating
From Wikipedia, the free encyclopedia
Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed (i.e. linked to the present day and thus calendar or sidereal time) or floating.
Archaeologists use tree-ring dating (dendrochronology) to determine the age of old pieces of wood. Trees usually grow rings on a yearly basis, with the spacing of rings being wider in good growth years than in bad growth years. These spacings can be used to help pin down the age of old wood samples, and also give some hints to climate change. The technique is only useful to about 4,000 years in the past, however, because it requires overlapping tree ring series.
The earth's orbital motions (inclination of the earth's axis on its orbit with respect to the sun, gyroscopic precession of the earth's axis every 26,000 years; free precession every 440 days[1], precession of earth orbit and orbital variations such as perihelion precession every 19,000 and 23,000 years) leave traces visible in the geological record. These changes provide a long-term sequence of climatic events, recorded as changes in the thickness of sediment layers(also known as "varve analysis"—the term "varve" means a layer or layers of sediment), as temperature induced changes in the isotopic ratios for oxygen isotopes in sediments, and in the relative abundance of fossils. Since these can be calibrated reliably over a period of 40 million years this provides an alternate verification to radiometric dating in cases where sufficient record exists to provide a reliable trace..[2]
Another technique used by archaeologists is to inspect the depth of penetration of water vapor into chipped obsidian (volcanic glass) artifacts. The water vapor creates a "hydration rind" in the obsidian, and so this approach is known as "hydration dating" or "obsidian dating", and is useful for determining dates as far back as 200,000 years.
[edit] Incremental dating techniques
[edit] See also
[edit] References
- ^ The axis of rotation is inclined 0.2 seconds from the axis of symmetry, with an observed effect that the axis of rotation moves about its axis of symmetry every ~440days. - Analytic Mechanics, Grant R. Fowles, 1962, Holt, Reinehart & Winston, New York
- ^ Telling Time, Nature, Nature Publishing Group, 2006, Volume 444/9, pp. 134
