Carbon-14 dates more than about 10,000 years old are subject to at least one serious error, which is (at the moment) not amenable to correction.

Wood pebbles from a single thin clay layer, in western Florida, give C-14 dates which range from 22,000 to 29,000 years, with no assurance that either of these dates is correct. C-14 dates from different wood fragments and other material in coastal zones appear to provide a data for a high stand of mean sea level during the Wisconsin at almost any time desired from 20,000 to 40,000 years ago or more. Not all of these dates can be correct, or there would have been no Wisconsin glaciation. For reasons having to do with the growth and decay mechanisms affecting continental glaciers, it is unlikely that any of these dates are correct. Regardless, there is no standard by which "good" dates can be distinguished from "bad" dates.

A suite of samples which has been dated by both C-14 and K-Ar methods yields dates which differ by 1 order of magnitude or more; either the "young" C-14 dates represent much older materials, or the "older" K-Ar dates represent much younger material. With no additional method of dating, one cannot be certain which type of date--if either--is correct. The likelihood of contamination is higher for the C-14 results, however, and therefore this suite of dates may include mid-Wisconsin numbers for mid-Pleistocene events.

Morner has reported that a small contamination of late Wisconsin or Holocene carbon may provide mid-Wisconsin dates for pre-Wisconsin materials.

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