What is material intrusion in carbon dating?
Material instrusion is an uncommon problem in some carbon 14 dating. For instance, in dating peat bogs, which may be very old, the samples often contain miniscule roots from newer plants that grew in the peat. Sometimes the roots, having decomposed, are indistinguishable from the older peat. What is tested might simply be a mixture of old and new material leading to erroneous results.
No one expected that material intrusion might be a problem with the Shroud of Turin. It was.