Correct. C14 is absorbed by living organisms while they are alive. Thus, when a tree is cut down and fashioned into a door post you need to understand that a C14 reading of that door post will tell you the approximate date that the tree was cut down. Since in a dry climate a door post might last 150 years that doesn't do a lot of good. But advances in the technique now allow them to carbon date pollen spores or cereal grains which have a much shorter life span than a tree. Thus, we can reasonably assume that pollen or grain found in a destruction layer most likely belongs there. Is it perfect? No. But until the Greeks got around to inventing coins c 700 BC in Asia Minor it is about the best we can hope for.
As far as contamination goes the assumption is that all samples are contaminated to some degree. This
http://www.radiocarbon.com/carbon-dating...atment.htm
will explain some of the techniques for cleaning the samples.
When the Shroud of Turin was C14 dated to the 12th century the religious nuts lost their minds and insisted that the sample had been contaminated by a fire! Computations were done on the amount of "contamination" needed to get the date back to the first century. It turned out to be roughly 45 pounds which is is about double the weight of the Shroud itself.
Religious nuts aside, scientists usually have a better understanding of this stuff than jesus freaks.
As far as contamination goes the assumption is that all samples are contaminated to some degree. This
http://www.radiocarbon.com/carbon-dating...atment.htm
will explain some of the techniques for cleaning the samples.
When the Shroud of Turin was C14 dated to the 12th century the religious nuts lost their minds and insisted that the sample had been contaminated by a fire! Computations were done on the amount of "contamination" needed to get the date back to the first century. It turned out to be roughly 45 pounds which is is about double the weight of the Shroud itself.
Religious nuts aside, scientists usually have a better understanding of this stuff than jesus freaks.
