Miles3: "Etude, thing is you're talking about the fossilisation process, and 14 C dating isn't used in those cases." I would have agreed with you if I hadn't found out that wood (possibly other organic matter) can petrify rather quickly. One source I found in Wiki-answers says it can happen in a matter of days, given the right cocktail of minerals. Another says that it can happen in less than 10 years (http://wiki.answers.com/Q/How_long_does_it_take_petrification_to_occur). I have to say that I didn't pursue to find the basis for that conclusion. However, I can't find any refutation either. So, I don't really know why 14 C would necessarily be excluded from testing fossilized material.
"most fossils are remineralised with silica" -- What I've found is that there are several things that influence petrifaction: Silification, Pyritization (iron and sulfur) and Replacement ( calcite, silica, pyrite, and hematite). And since 14 C can also make up water in addition to the "soup" that would contaminate a specimen, it's not unreasonable to question the process (petrifaction) as one that might influence and contaminate the readings.
"For making the difference between a specimen that has been perminaralised and one that hasn't, try burning fossilised wood." The process of 14 C extraction involves high-temperature pyrolysis-combustion. Yes, you can "burn" some "rocks". The whole point of it is to extract carbon in the form of CO 2 and then take a reading of nuclear decay.
"... it doesn't work like that. Athmosphere is global" Absolutely not! Veerabhadran Ramanathan, (UCSD and Harvard), one of the world's leading climatologists, pointed to an interesting situation regarding the distribution of contaminants in the air. He (and some colleagues) noticed the difference between the seemingly "unpolluted" Maldives Islands (because they don't have sufficient sources of pollution) noticing that only the southern tip of one of their islands is actually pollution "free". Apparently, The Maldives sit in swath of polluted air currents coming from India. But the "unpolluted" tip that has "clean air" is enjoying a current from Antarctica. Bottom line is that there are distinct currents and divisions in the atmosphere which can isolate the presence of contaminats. That has been a long standing suspicion. The measurements by Ramanathan between the part ofThe Maldives that is polluted and the part that isn't revealed a difference in the amount of sunlight that actually reached the ground.
Bottom line is this:
- I absolutely believe in the testing method and procedure and in the science behind 14 C testing.
- I don't doubt that the venues and results from 14 C testing are accurate.
- I do believe that different materials require different ways of testing.
- I do believe that many results (perhaps a majority) of 14 C testing definitely reflect accurate dates in the 10ths of thousands of years.
Clear enough? But I also think that the accuracy in age of some (not all) of the items tested can be skewed by the very reasons I'm arguing. But that's not the fault of the science and more a problem associated with the specimen. I've tried to reply to some of the assumptions I feel people have made about testing. The very controversy between scientists about the issue (the testing of the Shroud of Turin being one example and the questions about dendrochronology being another) is for me enough cause to not swallow the testing of everything hook, line and sinker.
In the process, it's easy to lose the fact that while I believe in the testing, I have some doubts about some conclusions for the reasons I've stated. I also believe that there probably is a preponderance of items tested that result in accurate dating. But what I simply tried to establish is that 14 C testing can provide incorrect age conclusion as well (in spite of having a lot of success) and that the reasons that happens may be beyond our control due to our lack of some knowledge about the original environment of the object we're testing, even if that only happens once in a while. In the discussion, I was merely offering reasons why that's possible.
Lastly, I never meant to insinuate that Earth's previous warming was due to a "water canopy". I merely mention that such is one possibility, heavy concentrations of CO 2 being another, the flipping of the magnetic field being yet another. I don't think you want me to find "remnants" of a water canopy, 'cause that would be just plain crazy. I base my guess on the strata revelations that show so many parts of the earth were once (not all at once) under water and on ice-core records, which show multiple occurrences of heavier CO 2 deposits. I really want to stick a fork in this one. I'm done.