Carbob dating

18 Dec

The approximate time since the organism died can be worked out by measuring the amount of carbon-14 left in its remains compared to the amount in living organisms.

As you learned in the previous page, carbon dating uses the half-life of Carbon-14 to find the approximate age of certain objects that are 40,000 years old or younger.

It takes about 5,730 years for half of a sample of radiocarbon to decay back into nitrogen.

It takes another 5,730 for half of the remainder to decay, and then another 5,730 for half of what's left then to decay and so on.

The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample.

By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: t = [ ln (0.10) / (-0.693) ] x 5,700 years t = [ (-2.303) / (-0.693) ] x 5,700 years t = [ 3.323 ] x 5,700 years Because the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old.

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For example, in 1991, two hikers discovered a mummified man, preserved for centuries in the ice on an alpine mountain.Once an organism dies, it stops taking in carbon-14.The carbon-14 it contained at the time of death decays over a long period of time, and the radioactivity of the material decreases.C-12 is by far the most common isotope, while only about one in a trillion carbon atoms is C-14.C-14 is produced in the upper atmosphere when nitrogen-14 (N-14) is altered through the effects of cosmic radiation bombardment (a proton is displaced by a neutron effectively changing the nitrogen atom into a carbon isotope).The new isotope is called "radiocarbon" because it is radioactive, though it is not dangerous.It is naturally unstable and so it will spontaneously decay back into N-14 after a period of time.Since Nitrogen gas makes up about 78 percent of the Earth's air, by volume, a considerable amount of Carbon-14 is produced. This is how carbon dating works: Carbon is a naturally abundant element found in the atmosphere, in the earth, in the oceans, and in every living creature.­ ­As soon as a living organism dies, it stops taking in new carbon.The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced.