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One needs to consider several possibilities here, such as vegetational changes, oscillations of climate and environmental p H, or whether a site may have been covered by sediment”to satisfy the requirements of the microerosion dating method, at least two regional calibration curves would be obligatory.
Regrettably, there was not enough time available to determine locally precise multiple calibration curves At Côa Valley (Portugal) the calibration curve of Onega Lake (Russia) was applied, the only available in Europe!
Then, the current amount of radioisotope is compared to the amount of stable element into which it is slowly changing. However, evidence has mounted that radioisotopes underwent a period of radical acceleration of decay in the past.
This evidence has indicated that radioisotopes have not decayed at a constant rate, and therefore the radiodating "clocks" in general are all broken.
During NEWS ‘95, the international rock art congress (and also IFRAO meeting) held in Turin, it was clearly pointed out that each “new” research method should work in a close relation with other parallel approaches, here mainly including the archaeological one.
Each attempt to separate rock art research (which we would like to call “Rupestrian Archaeology”) from archaeology is simply unacceptable. Loendorf (5) about cation-ratio varnish dating: “…under the direction of an archaeologist, more than half of the samples were collected to test the validity of the cation-ratio dating method.
They then used these measurements to estimate an age for the bone.
But radiodating cannot proceed without some primary assumptions: the starting conditions of a given sample (e.g., how much of each isotope was present in the beginning), a steady rate of decay of certain radioactive isotopes of elements called radioisotopes, and a lack of tampering with the system (e.g., elements added or subtracted since the radioisotope "clock" first began counting time).
We can find a detailed explication in Archaeometry 34 (6).Most of these test samples were selected to measure the numerical age of a petroglyph for which there was good relative evidence as to its age…”.So called blind-tests conducted at Côa have been conducted with different rules, assuming “a priori” their validity, completely unrelated with any other local archaeological research.There was not enough time available to determine a local calibration curve!But we can see in a picture (Archaeometry) that Onega Lake engravings have been executed on a horizontal surface.
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Correcting with more measurement and geometrical relationships the Cernohouz and Sole method (1966, which measured the retreat from the supposed “fresh” edge of a cristal to the actual edge), and knowing the weathering rate, it is possible to obtain the period of exposition of a (mostly quartz) crystal truncated by the engraving activity. 879) The oldest date assured by the micro-erosion method (at Canada do Inferno) was “about E6500 -2000 BP” (-7-, p.