Wikipedia ar ar dating
Wikipedia ar ar dating
At the end of the series of experiments, the step ages (± one sigma errors are quoted herein) are plotted against the cumulative amount of ).This approach is designed to look at the gas released from sites of increasing argon retentivity.
For plateau ages, I list the standard error on the mean (the SEM).Any two points in the universe lie on a straight line!In evaluating isochron “goodness of fit parameters”, the number of degrees of freedom for Chi Square Tables is N-2, and for two steps, this is zero.The plateau age of 100.00 Ma, with a standard error on the mean: of ± 0.22 Ma is found to be unacceptable, with p ~ 0.003 ( lie between ~ 99 and 101 However, its exact value, and equally important its error estimate, cannot be stated with statistical confidence.The first is due to the presence of excess (1999) showed that almost all the ages were untenable as crystallization values.
In this web page, I take a similar approach (but one that is somewhat easier to visualize) to evaluate these ages based on their age spectra. Elsewhere it will be shown that this conclusion is fully supported by critical examination of the individual age spectra.
Evaluation of the corresponding isochron plot gave MSWD = 3.9 (Both the plateau and isochron approach statistics are unequivocal – a large amount of excess scatter is present in the data sets (“geological error”).
This mineral separate fails to yield either a plateau or an isochron age.
However, in many instances, the published “ages” have no merit, as they fail the simple statistical tests that should be applied to all such data. In these experiments, a sample is heated in steps of increasing laboratory extraction temperature, until all the argon is released.
The argon released in each step is measured to calculate a “step age” with an associated analytical error.
An adjunct method of evaluation is to present the relevant data on an isotopic ratio plot and look for straight-line segments through three or more consecutive heating steps. The resultant “goodness of fit” parameter, in tandem with the number of points on the line, must be evaluated for statistical reliability (95% confidence level generally) using Chi Square Tables (, 1992).