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Argon/argon dating works using only the ratio of the concentration of the argon isotopes. For the purposes of this debate, "accurate" means that 95% of the dating errors are within 10% of the measured date, within the time span for which the isotope pair is utilized.Since carbon dating depends upon variable cosmic ray intensity, a calibration curve is assumed to be applied to account for that.other isotope pairs cover intermediate time periods between the spans for carbon 14 and uranium.Some radiometric dating methods depend upon knowing the initial amount of the isotope subject to decay.For dating back to about 35,000 years, sediment layers are precise. Sediments include different types of pollen depending upon the season.Consequently, individual years can be identified by season, so there is no possibility of layers being confused.Measuring the ratio of C14 to C12 and C13 therefore dates the organic matter for periods back to about eight half-lives of the isotope, 45,000 years.
When the carbon dioxide, containing C14 as well as stable C12 and C13, is taken in by plants it is no longer exposed to the intense cosmic ray bombardment in the upper atmosphere, so the carbon 14 isotope decays without being replenished.The coral record verifies that radiometric methods are accurate. For the purposes of assessing accuracy, each of the methods is assumed to be applied in accordance with the established methods and technology.By analogy, a stop watch will not keep accurate time if it is not wound, if it is not in good repair, or if the operator forgets to press the button.Every few years, new geologic time scales are published, providing the latest dates for major time lines.Older dates may change by a few million years up and down, but younger dates are stable.