summary格式代写|文献综述代写
微信：eq3hao 网站：http://essayquality.com
EssayQuality提供：summary格式代写、文献综述代写、mla格式代写、网课代写、网课代考、apa格式代写….
Fission track dating attempts to calculate the age of a mineral or glass by using either of two methods being spontaneous or induced, which engages (‘two different isotopes of uranium, U-238 and U-235 respectively’) (Walker, 2005: 115–117). Most uranium decays into a stable lead but occasionally the atom splits in two at a high speed damaging the surrounding structure. By observing a polished slither of the material under an electro-microscope you can see the tracks left by this (spontaneous fission), then by counting the fission tracks left behind, it is possible to calculate an age for the object in question (Bahn 2008:152–154; Greene 2002:170–171; Walker, 2005: 115–117).
Obsidian hydration:
Irving Friedman and Robert Smith developed obsidian hydration (rind) dating in 1960. If an obsidian (recently deposited volcanic) object, is trapped for a long period in an area where water is present, water vapour will slowly diffuse into a freshly chipped surface. The cumulative hydration or absorption of water will form a hydration layer, measurable in microns on the exposed surfaces. These layers are then detected, when a small section of the object is removed, ground, and placed on a microscope slide, where the hydrogen band is measured (Bahn 2008:159–160; Greene 2002:175–176; Trembour and Friedman 1984: 141–152).
Since the hydration rate, with respect to a specific obsidian composition and water temperature is constant, if the obsidian composition is known and the historical temperature of the area was constant year after year, or if regional correction factors are known, accurate dates can be produced. In the right circumstances, this technique can be used to date objects as recent as present or as ancient as 120,000 BP (Bahn 2008:159–160; Greene 2002:175–176; Trembour and Friedman 1984: 141–152).
