Talk:Radiocarbon dating

From Academic Kids

Contents

1 Constant cosmic ray flux assumption 2 Calibration curves as basis for dating 3 Standard deviation 4 Kudos 5 Calibration Curves

Constant cosmic ray flux assumption

Since it is assumed that the cosmic ray flux is constant over long periods of time, carbon-14 is assumed to be continuously produced at a constant rate and therefore that the proportion of radioactive to nonradioactive carbon throughout the Earth's atmosphere and oceans is constant.

I'm pretty sure the above is false since:

Beryllium 10 is useful for studying the geology from hundreds of thousands of years ago mainly because it has a half-life of about one and a half million years. In addition, there are two key factors that have affected beryllium 10 production over the last 200,000 years: the earth's magnetic field and the sun's magnetic activity. When there are high-intensity solar magnetic storms, more charged particles are interacting with cosmic rays, and less beryllium 10 is produced. Likewise, the earth's magnetic field changes the flux of cosmic rays into and out of the atmosphere. EurekAlert (http://www.eurekalert.org/pub_releases/2002-06/dc-1c060602.php)

-In response to the above: The solar storms only cause a cosmic ray influx in the short term, in the long term it's either negligable or included as part of the average rate of production.

-In response to the above: The current rate of C14 decay is not as large as the current rate of C14 production (differences of 15-30% are quoted).

-Because of calibration curves, this assumption doesn't have to be true for C14 to accurately measure the age of an object (I've added this statement to the article). Samboy 20:50, 11 Apr 2005 (UTC)

Calibration curves as basis for dating

Is it your position that the calibration curves are the basis for radiocarbon dating accuracy? If so, then what is your position on the bristlecone pine measurements that I posted in the dendrochronology talk page? Wdanwatts 02:27, 12 Apr 2005 (UTC)

My position is that the assumption that C14 levels have been fairly constant is a reasonable starting base for dating items. However, this assumption is not necessary because of the existance of calibration curves. Basically, we get almost the same namers from calibration curves that we get from just assuming that C14 levels have been constant for the last 10,000 years. We have two independent ways of getting at the same data. The chances of both methods giving us mostly the same data by pure chance is really small. Samboy 02:36, 12 Apr 2005 (UTC)

Is not the fact that the calibration curves make "small" corrections sufficient to ensure consistency between the results with or without "calibration"? How does that bolster the results? Dan Watts 13:51, 16 Apr 2005 (UTC)

Standard deviation

Is is really the standard deviation that is indicated by +/- ? That should indice the e.g. 95% confidence limit. The difference is (at least) a factor of two!)

Kudos

Great article! --Yak 16:50, Feb 22, 2004 (UTC)

Calibration Curves

Please educate me as how speleothems (which appear to mainly use U/Th means for dating) can be used to calibrate C14 dating. It looks like using a yardstick to calibrate a micrometer. Wdanwatts 18:35, 13 Apr 2005 (UTC)

Speleothems, at least some of them, have layering due to variations in seasonal precipitation, etc. The calcium carbonate of the speleothem uses CO2 from the air & water. The older end of the C-14 scale can be matched with the shorter end of the U-Th scale, presumably. The question I have here is the ancient carbon in the waters that was dissolved out of the limestone by the water on the way to the speleothem. Vsmith 20:35, 13 Apr 2005 (UTC)

As long as I am asking, how about some explanation of how the sources listed in the article --ice and deep ocean cores, lake sediment varves, and coral--, (all but dendrochronology) contribute to the C14 calibration. To me, the links look to have tenuous (at best) connections to C14 calibration. Wdanwatts 19:43, 13 Apr 2005 (UTC)

Ice cores have annual layers which are countable. The cores also contain inclusions of trapped air which contains CO2 and therfore C-14. Deep ocean seds and lake varves are layered sediments w/ presumably annual layering, these contain carbon within the seds that has C-14. Coral is built by organism in crude? layers and carbon is present from the corals. Correlate the layering - check with C-14 dates.

Hope this simple explanation helps, although there is a lot more in the details and I may have mixed things up a bit :-). Vsmith 20:35, 13 Apr 2005 (UTC)

Perhaps you could put that in the Ice cores article. It tells of needing 2000 to 6000 annual layers of snow to becom impermeable to air. I don't see how having an averaging factor that large can allow much calibration of the C-14 dates. Wdanwatts 12:51, 14 Apr 2005 (UTC)

Hmm.. just read that, and it does state that correlation problems exist. Looks like the ice core article is currently undergoing some revision by Tonderai with some references. More to explore there, cheers. Vsmith 13:57, 14 Apr 2005 (UTC)

There is a lot to explore there. When searching in the ice field of research, remember to also search for "firn" and "snow pit". (SEWilco 06:01, 16 May 2005 (UTC))