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Please begin with an informative title:

'History isn't dead. It's not even past.' - William Faulkner

Not as well-known as microwave ovens, carbon dating is how scientists gauge the age of some long-dead life. As a chemical element, carbon comes in several isotopes. The mix of isotopes in an object tell how long it's been dead. Isotopic analysis tells us that.

The most common form (or isotope) of carbon. 12C, has an atomic weight of 12, and is stable. There is also a heavier stable version, 13C, and a still heavier radioactive version 14C, that decays to 12C with a half-life of 5,730 years. Living animals and plants constantly have their 14C replenished from the air and water, but dead things lose theirs. Samples of dead life can be tested for how much 14C is present. The less there is, the longer the sample has been dead. In 1960, Willard Libby was awarded the Nobel Prize in chemistry for figuring this out in the late 1940s. There are other elemental isotopes with longer half-lives that are used to date older samples, like potassium-argon and uranium-lead. But the principle is the same.

Back to carbon: It seems that plants prefer 12C to 13C. They have about 2% less 13C than is in the atmosphere. So as fossil fuels are burned, the ancient carbon is released into the atmosphere and dilutes the 13C. From RealClimate:

[A]t no time in the last 10,000 years are the 13C/12C ratios in the atmosphere as low as they are today. Furthermore, the 13C/12C ratios begin to decline dramatically just as the CO2 starts to increase — around 1850 AD. This is exactly what we expect if the increased CO2 is in fact due to fossil fuel burning.
And it's not as if we've been replacing 13C with 12C. All the original 13C and 12C are still there. We've added to it - to levels not seen in over 15 million years.

So what we get is more carbon dioxide with a smaller fraction of 13C all the time. The only way for that to happen is for the ancient 13C - free carbon to be released, via human combustion of fossil fuels.  As of last week, Mauna Loa was at 398.41 PPM - 2.33 PPM higher than this time last year; 20.37 PPM over 10 years ago; and almost 120 PPM higher than the pre-industrial levels.

We are frogs in a boiling pot, we lit the fire, and we are still adding more fuel it.


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Originally posted to Tom Lum Forest on Mon Apr 22, 2013 at 11:05 PM PDT.

Also republished by SciTech.

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