Because 14 C has a short half life, its use for dating is limited to about 8 or 9 half-lives or 50,000 years. Materials suitable for dating include wood, peat, shells, CaCO 3 accumulations, and bone. Sample size can be a problem. Usually, several grams of C are needed to get a measurement on the mass spectrometer. In many areas of Midwest, Wisconsin glaciers advanced quickly over forests and buried them.
Wood is preserved in the till deposits.
This wood is excellent for 14 C dating. 14 C dates for Wisconsin deposits are considered to be very accurate. Varies - depends on many factors. This rate needs to be adjusted to account for losses of soil due to geologic erosion.