h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

It seems to me that it was just presumed that there had always been the same amount of C14 in the atmosphere, when the method was invented. Didn't it take a really long time before they started calibrating it? And apparently some findings of stalagmites has shown some variances in time we didn't know about. Doesn't that mean it is quite inaccurate, when we didn't pick this up in the calibrations earlier?

I think dates before the 1970s may not be entirely accurate. But I don't know what degree of inaccuracy we are talking about even then.

You're right Alan, they can be if you are looking at dates which are written up in normal terms (ie if you read a book from 1968 saying 'the site was dated to 800BC using radiocarbon').

If you know you have an uncalibrated date, you can run it through modern calibration programs to find the calibrated date, but you need to know the error on the original count otherwise its pretty well useless.

An additional problem is that Libby's original half life estimate was 5568 years (AFAICR), and I'm not sure when that was replaced with the current t1/2 time.

Konrad

I think the need for calibration was realised fairly early on, some time in the 1950s. Although there was as a debate for a while as to whether the radiocarbon or historical dates of Egyptian artefacts were in error. It may have been some time before accurate calibration was available.
The radiocarbon timeline is well calibrated up to 15000 years ago, beyond that there is some recent evidence that radiocarbon levels may have changed much more than previously thought. See http://news.bbc.co.uk/hi/english/sci/tech/newsid_1413000/1413024.stm

additional problem is that all the nuclear testing and stuff that has gone on recently has screwed up the C14 level for this past century. Although it will be many years before we are far ebough distant that the 20th century can be carbon dated there is still going to be major problems calibrating for all the radioactivity that has been added over and above what might naturally occur.

Good article by the way. Does any one kinow any more about the Clorine testing, never heard about that one.

FABT

There is also a problem with dating omnivores and carnivores, as fish use take up carbon with a different ratio to plants. see http://www.bbc.co.uk/h2g2/guide/F76869?thread=141543&post=1322482#p1322482 for more info.

It takes time to reach that equilibrium of C-14 in the atmosphere, yes? So if the concentrations started at 0% in the past 30000 years, the whole dating system would be completely screwed. Also, the solar weather could greatly affect the C-14 levels, to an extent that we know not, having never experienced a large solar event in living memory.

~gareis