originally posted by: Another_Nut
Why read any of the reports as they will all be wrong?
If your "constant" is fluctuating then to use it as a timekeeper is ridiculous
C14 doesn't fluctuate that much. Perhaps you mean the half life of C14 is fluctuating?
I read about a weird effect our sun has regarding this, but the effect is so small that it might change a C14 date by a week or two, and only if the
C14 date was old enough (say, 30-50 thousand years.)
C14 reports give two dates - the "radiocarbon years" date and the estimated actual years. The radiocarbon years date is fitted to a calibration curve
that is based on ages of materials that can be verified through other means, such as pottery styles, actual dated but ancient written materials,
geological evidence like varves, coral growth and tree ring analyses.
The calibration curve is adjusted when new info arises.
The variation is always well represented in the date ranges given from C14 testing. The much older dates come with much wider ranges of reliability -
given as plus or minus so many years.
It's not as if you can use C14 to pin down to the exact year how old a 40,000 year old object is.
But you can get almost that close with something 5,000 years old.
originally posted by: Another_Nut
How do c14 and all other decaying isotope timekeepers, work?
C14 decays into C12 at a known rate, a rate verified thousands of times through a well-known process that has been completely explained in particle
C14 (and C12) is ingested by living organisms through either eating or breathing. Plants take it in during photosynthesis. Ingestion (of course)
stops when the organism dies. The theory is that, at death the ratio of C14 to C12 in the organism is set. So, years later, some of the C14 will have
decayed into C12. Since we know how long it takes for C14 to decay (because we know its half-life,) it is possible to estimate how long it has been
since the material last ingested carbon.
Obviously, you have to have an assumption about what the ratio of C14 to C12 was during the organism's lifetime in order to have a starting point from
which you can calculate how much C14 had decayed into C12, thus the calibration curves I mentioned.
It's not exact, but it is certainly no where near useless. If one cares to examine the world in enough detail, it is possible to estimate the
fluctuations in the C14 to C12 ratio over pretty much the entire span of years C14 can be used for.
See, since it does decay, if the material is too old, there might be no C14 left in it at all. That's an oversimplification of it, but that's why
it's no good beyond about 60,000 years before the present. It's actually about eight half-lifes and then it's shot. Beyond that age, the material has
too little C14 in it to reliably test.
What I meant by old carbon contamination is that shellfish absorb old carbon more than most organisms because they live on the sea floor where shells
have been crumbling for eons, leaving behind carbon that's already yielded most if not all of its C14. Some animals eat coral, which also absorbs old
carbon from seawater for similar reasons.
Animals that eat shellfish a lot also get their C14 ratios skewed because of the low C14 in the shellfish they ate.
Animals that live in caves like fish in cave streams, even streams coming out of caves, can also have this problem. Same for objects like wooden
spears or even bones, both of which intake old carbon from the water they're in (some of which cannot be separated from the original carbon in the
object.) Limestone has a high carbon content and is dissolved in cave water (that's how caves are formed.) And limestone (understandably) contains
very little C14.
It is impossible to use C14 dating on an organism that is still alive. These days, we are constantly spewing out old carbon - some of the oldest
carbon in the world comes out of our smokestacks and tailpipes. We are ruining C14 dating for any future civilization unless they can find our
records of atmospheric carbon isotopes pretaining to our own time period.
edit on 6/23/2014 by Harte because: I screwed up