Carbon 14 in fossils?

The argument is basically garbage. The C-14 is due to contamination of one sort or another; this is proven by the fact that the amount of C-14 in such old samples doesn't correlate with much of anything yet there are lots of correlations with the amount of C-14 in younger samples. The amount is far too small to affect the dating of younger samples. They're trying to convince you that all C-14 dates are suspect because the amount doesn't go exactly to zero as we look at older and older samples with incredibly sensitive instruments.The Earth is far older than 6,000 to 10,000 years, and so is life, no matter how much C-14 is found in Phanerozoic samples. Real scientists are trying to extend the useful range of the method and running into diffculties. Big surprise, big whoop.As for where the contamination comes from, well, it's such an incredibly tiny amount that it's hard to figure that out, and research is ongoing. Air and groundwater infiltration, formation in-situ, ... there's lots of possibilities.There's a good article on the subject at Carbon-14 in Coal Deposits

C-14 can be produced from, IIRC, C-12 by a fairly rare collision with a particle given off by a decay in the Uranium or Thorium series. That is, the expected level of C14 in a diamond is a function of its exposure to Uranium or Thorium.Note that the creationists got a reputable lab to do the measurements, but they did not subtract the background.There's some more discussion here, but I couldn't find the useful information in a quick perusal.

The measurements were by mass spec. The actual AGU poster is available at The Enigma of the Ubiquity of 14C in Organinc Samples Older than 100Ka (a PDF; the diamond stuff is at the bottom, just to the right of center). Above the diamond stuff is a notation that background was subtracted from their other measurements.The results do indicate that ther's a tiny bit of 14C in there. However, this is a problem if and only if the only means of 14C production is in the upper atmosphere, which is known to be false. The vast, vast majority of 14C is produced up there, but not all of it.

Not a lot. It does have something to do with reassuring the already-convinced who are not knowledgable enough to realize that this kind of effect would change the vast majority of 14C dates by a small fractionof a percent. It's an issue for those trying to extend 14C dating beyond 50 Ka or so.

In theory, yes. In practice, not very often if ever."Simple" methods such as carbon dating and K-Ar dating are susceptible to contamination errors. This is known, as are methods that are nearly guaranteed to avoid contamination."Age-diagnostic" methods such as isochrons, Ar-Ar, and U-Pb concordia-discordia are extremely unlikely to yield an older-than-actual age. These methods either produce a date and an assessment of the reliability of that date, or they don't produce a date at all. They are by far the most widely-used methods.Then you start dating things by different methods and getting the same age from each method. And you compare results to non-radioisotope methods, and again they agree.It is not possible that all radiometric age determinations are tremendously wrong, as the YECs would have us believe. That would be like you winning the lottery grand prize a billion times in a row. Neither is going to happen.See Correlation Among Various Radiometric Ages and Radioisotope dating links and information.

IMHO that's a fairly small group, not all YECs. Most YECs don't get beyond "Creationist X got the wrong result for formation Y therefore the Earth is 6,000 years old".Wodmorappe tried the line you wrote, but he's fairly sophisticated for a creationist; his quote-mines and claims sound pretty good to the less-educated YECs who want to believe. But Henke called him on it at How Can Woodmorappe Sell Us a Bill of Goods if He
Doesn't Know the Costs?. I haven't seen that particular argument raised by anyone else.