Just started "The Bible Unearthed"

[Minimalist]

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.

[Wyrd of Gawd]

I just started this book. I know that I am going to have a lot of questions. Anyone here pretty well educated on this topic and willing to field some questions as they come up? One general question, how are archeologists able to make sure (or close to) conclusions based off of centuries old cities? Like these cities that are 2500-3000 years old, sometimes I read about new discoveries based off of a pottery shard or something like that. I saw Pompeii recently and was amazed by its preservation, but this is a major anomaly right? Most cities aren't preserved by layers of volcanic ash. Anyway, thanks for the help

They found horse shit from Hannibal's horses when he crossed the Alps to invade Italy in 218 BC, about 2,234 years  go.

http://www.dailymail.co.uk/sciencetech/a...Italy.html

[Won2blv]

So have there been tests on radio carbon dating compared to otherwise datable events Like the explosion of Mt Vesuvius? Has any of the organic material from Pompei, Herculaneum, or the other surrounding cities been successfully dated to 79CE? I know I can google this but its more interesting hearing it from you

[Minimalist]

If memory serves one of the original test parameters for carbon dating was bread from Pompeii because the date is so well fixed in the historical record.