You can find some further good information here: -- read the full page if you get the chance.
Carbon dating has a certain margin of error, usually depending on the age and material of the sample used.
We believe all the dates over 5,000 years are really compressible into the next 2,000 years back to creation.
So when you hear of a date of 30,000 years for a carbon date we believe it to be early after creation and only about 7,000 years old.
These include the starting conditions, the constancy of the rate of decay, and that no material has left or entered the sample.
Furthermore, if a sample has been contaminated, scientists will know about it.
This standard content of C14 can then be used for wood not associated with a historically documented date.
If you have any more questions about it don't hesitate to write.
(2.) I just listened to a series of lectures on archaeology put out by John Hopkins Univ.
So they tested some of the ring sequences by C14 to put the sequences in the 'right' order.
Once they did that they developed the overall sequence.