Carbon Dating Explained
What is Radiocarbon Dating?
In this section we will explore the use of carbon dating to determine the age of fossil remains. Carbon is a key element in biologically important Carbon dating is based upon the decay of 14C, a radioactive isotope of carbon with a relatively long half-life ( years). While 12C is the most abundant carbon isotope, there is. Carbon dating is a variety of radioactive dating which is applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for Krane points out that future carbon dating will not be so reliable because of changes in the carbon isotopic mix. This is the basic idea behind carbon dating. So in the real world, looking at a sample like say a bone dug up by an archaeologist, how do we know how much carbon 14 we started with? However it is possible, when dating very old rocks for instance, to use longer lived isotopes for dating on a longer time scale.
Beauty is the first test: Question How is carbon dating done? William Baker Answer Carbon 14 C14 is an isotope of carbon with 8 neutrons instead of the more common 6 neutrons.
It is unstable, and scientists know that it radioactively decays by electron emission to Nitrogen 14, with a half life of years. This means that given a statistically large sample of carbon 14, we know that if we sit it in a box, go away, and come back here years, half of it will still be carbon 14, and the other half will have decayed.
This effect is accounted for during calibration by using a different marine calibration curve; without this curve, modern marine life would appear to be years old when radiocarbon dated. Moving away from techniques, the most exciting thing about radiocarbon is what it reveals about our past and the world we live in. For both the gas proportional counter and liquid scintillation counter, what is measured is the number of beta particles detected in a given time period. By this method the scientist can keep track of how many atoms are decomposing per minute and per second. The unstable carbon gradually decays to carbon at a steady rate.
Or in other words, if we have a box, and we don't know how old it is but we know it started with carbon 14 atoms, and we open it and find only 50 carbon 14 atoms and some other stuff, we could say, 'Aha!
It must be 1 carbon 14 half-life or years old. So in the real world, looking at a sample like say a bone dug up by an archaeologist, how do we know how much carbon 14 we started with?
He was able to calculate the amount of Carbon in the atmosphere, before the industrial revolution, and adjust his equation accordingly. In photosynthetic pathways 12 C is absorbed slightly more easily than 13 Cwhich in turn is more easily absorbed than 14 C. Solving for the unknown, kwe take the natural logarithm of both sides.
That's actually kind of cool. It's a semi-long story, so bear with me. In the atmosphere, cosmic rays smash into normal carbon 12 atoms in atmospheric carbon http://minimoving.info/ke/the-dos-and-donts-of-online-dating.phpand create carbon 14 isotopes. This process is constantly occurring, and has been for a very long time, so there is a fairly constant ratio of carbon 14 atoms to carbon 12 atoms in the atmosphere.
Now living plants 'breathe' CO 2 indiscriminately they don't care about isotopes one way or the otherand so while they are living they have the same ratio of carbon 14 in them as the atmosphere.
Animals, including humans, consume plants a lot and animals that consume plantsand thus they also tend to have the same ratio of carbon 14 to carbon 12 atoms. This equilibrium persists in living organisms as long as they continue living, but when they die, they no longer 'breathe' or eat new 14 carbon isotopes Now it's fairly simple to determine how many total carbon atoms should be in a sample given its weight and chemical makeup.
And given the fact that the ratio of carbon 14 to carbon 12 in living organisms is approximately 1: In actually measuring these quantities, we take advantage of the fact that the rate of decay how many radioactive emissions occur per unit time is dependent on how many atoms there are in a sample this criteria leads to an exponential decay rate.
We have devices to measure the radioactivity of a sample, and the ratio described above translates into a rate of Voila, now you can tell how old a sample of organic matter is.
How to Do Half-Life Problems of Radioactive Isotopes
Carbon 14 dating is not great for dating things like a year old because if much less than 1 half-life has passed, barely any of the carbon 14 has decayed, and it is difficult to measure the difference in rates and know with certainty the time involved. On the other hand, if tons of half-lives have passed, there is almost none of the sample carbon 14 left, and it is really hard to measure accurately how much is left.
Since physics can't predict exactly when a given atom will decay, we rely on statistical methods in dealing with radioactivity, and while this is an excellent method for a bazillion atoms, it fails when we don't have good sample sizes.
However it is possible, when dating very old rocks for instance, to use longer lived isotopes for dating on a longer time scale. For more info on carbon dating go to: Radiocarbon 14 Web How is carbon dating done? Science Quote 'The mathematician's patterns, like the painter's or the poets, must be beautiful; the ideas, like the colours or the words, must fit together in a harmonious way.