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Additionally, I have a question about the whole Carbon-14 thing.

Now, I'm not a scientist in any such respecting such archaelogy or historical studies, but I am of scientific background. Just not that branch.

However, I don't recall the half-life of U237/9 (whatever it is) specifically, but I thought it was around 1500 years. In any case, since I went to college I've wondered how this carbon-dating could figure anything *older* than that? W/the Shroud, I've always thought that if it's around 2000 years, how could this method ever possibly prove it to be so?

I don't know enough about carbon dating to comment one way or another, but I do know that testing the Shroud using any such method is inherently risky because of the attempts that were made to repair the Shroud after it was damaged in a fire back in the Middle Ages.

If I remember, it works like this, regular carbon is carbon 12. carbon 14 is a slightly radioactive isotope, it's taken in, along with the carbon 12 by respiration (all living things).

When they stop respiration (dead) the ratio of carbon 12 to 14 tells you how long ago they stopped respiration.

C-14 has a half life of 5730 years. So if you have living plant material, you can figure out how much C-14 it has taken up in its living tissues based on reference material like bristlecone pine samples and known atmospheric concentratins of C-14 (it is made continuously from cosmic ray bombardment of nitrogen).

Once the plant has died, no new carbon is being incorporated and what is C-14 is there, decays away without replenishment.

Let's assume that the original plant material (wood, linen, cotton) contains a milligram of C-14. After 5730 years, there is half a milligram (one half-life). After 11,460 years there is a quarter milligram, or half of what there was at 5730 years.

So how far back you can measure depends upon how sensitive your detection technique is. You have an estimate of how much there should be if it were new, and measure how much there is now (you count beta particle emission rates and spectra, or use sensitive GCMS) and also measure C-14 decay products.

If you are using uranium, you look at the U/Pb ratios and 238/235 ratios. Uranium has a half-life of about 4 billion years, so it is useful in ating rocks but not such ephemeral things as people or plants.

National Geographic had an article about radiocarbon dating a few years back that explains things much better than I can.

I don't recall the half-life of U237/9 (whatever it is) specifically, but I thought it was around 1500 years. In any case, since I went to college I've wondered how this carbon-dating could figure anything *older* than that? W/the Shroud, I've always thought that if it's around 2000 years, how could this method ever possibly prove it to be so?

Well for starters carbon 14 dating has to do with ratios of carbon isotopes not uranium. That said, the 1500 year half life doesn't preclude measurements far longer than that. After 1500 years half is gone, after 3000 years 3/4 is gone etc. etc. I don't recall what the upper limit in age is for the carbon 14 process, but it is several factors longer than the half-life, I think 50,000 years is still reasonable with a large enough sample. The only real limiting factors would be the precision of the measuring instruments and the quantity of material being analyzed.