isochron

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isochron

[′ī·sə‚krän]
(geochemistry)
A line on a graph defined by data for rocks of the same age with the same initial lead isotopic composition, the slope of which is proportional to the age. Also known as geochron.
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Our data from various layers of Bilong Co oil shale do not define isochrons, indicating one or some of the four conditions determining accurate and precise depositional ages for shales with the [sup.
North Dakota, yielded a Re-Os isochron age of 354 [+ or -] 49 Ma ([lambda] = 1.
We believe the rate of helium diffusion from zircons, the presence of polonium radiohalos near uranium radiohalos in granite, the discordance of isochron dates among multiple conventional dating methods, and the presence of measurable concentrations of carbon-14 in coal and diamonds as explicated in our book provide strong evidence for a young earth.
The RATE group shows large discordances in isochron estimates of the age of rocks and minerals to be normative and as large as factors of two or three in some cases, much larger than the 15% Isaac stated in his review.
Subsequently, they used spatial interpolation methods to generate isochron maps that plotted the mean rates of spread of farming (and of the disappearance of hunting and gathering) in two dimensions (Ammerman & Cavalli-Sforza 1984).
The procedure was first used to produce an isochron map using Ammerman and Cavalli-Sforza's data (Figure 2) and then, using the new data-base, for Mesolithic sites (Figure 6) and Neolithic sites (Figure 7).
1984) reported a 934 [+ or -] 82 Rb/Sr isochron from granitic gneiss.
The claim that the earth is approximately 6,000 years old is supported from biblical interpretation and from four areas of scientific studies: helium diffusion in zircons, radiohalos in granites, isochron discordances, and the presence of trace amounts of carbon-14 (C-14) in pre-Cambrian material.
Sm-Nd isochrons have an advantage over Rb-Sr isochrons in that rare-earth elements (REE) like Sm and Nd are relatively immobile during geologic heating events, and, therefore, are unlikely to diffuse into or out of rocks.
To obtain crystallization ages, geochronologists also commonly employ the graphical isochron and concordia methods.
It must be understood that coexistence refers to the simultaneous presence of cultural attributes of the two metapopulations, on the same geographical area, at the definition scale of the isochrons.
But it would seem that in its broad outline it is relatively stable, at the degree of definition of the isochrons, due to the spatial correlation of the data taken as a whole.