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Isotope dating problems

Another problem derives from the “reservoir effect” in which old material, limestone or graphite, has contaminated the samples. This is particularly true of marine samples and contemporary shells may seem to be hundreds of years old.

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Half-life is the amount of time it takes for half of the parent isotopes to decay. In another 5,730 years, the organism will lose another half of the remaining C-14 isotopes.These samples are carefully cataloged and analyzed with a mass spectrometer.The mass spectrometer is able to give information about the type and amount of isotopes found in the rock.After one half life, it would have had 1/2 the carbon.And then after another half life, half of that also turns into a nitrogen-14.One standard deviation has a 68% probability and two standard deviations have a 95% probability.

Radiocarbon dating has had an enormous impact on archaeology around the world since it made it possible to date carbon and wood could be directly without dependence on characteristic artifacts or written historical records.

So carbon by definition has six protons, but the typical isotope, the most common isotope of carbon is carbon-12. And then that carbon dioxide gets absorbed into the rest of the atmosphere, into our oceans. When people talk about carbon fixation, they're really talking about using mainly light energy from the sun to take gaseous carbon and turn it into actual kind of organic tissue.

But what's interesting is that a small fraction of carbon-14 forms, and then this carbon-14 can then also combine with oxygen to form carbon dioxide.

When this method was first developed, a fairly large amount of carbon was necessary for dating but use of the AMS (accelerator mass spectrometer) today necessitates only a few milligrams for analysis.

What I want to do in this video is kind of introduce you to the idea of, one, how carbon-14 comes about, and how it gets into all living things. They can also be alpha particles, which is the same thing as a helium nucleus. And they're going to come in, and they're going to bump into things in our atmosphere, and they're actually going to form neutrons. And we'll show a neutron with a lowercase n, and a 1 for its mass number. And what's interesting about this is this is constantly being formed in our atmosphere, not in huge quantities, but in reasonable quantities. Because as soon as you die and you get buried under the ground, there's no way for the carbon-14 to become part of your tissue anymore because you're not eating anything with new carbon-14.

This process continues over time, with the organism losing half of the remaining C-14 isotopes each 5,730 years.