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Ever wondered how scientists know the age of old bones in an ancient site or how old a scrap of linen is?

The technique used is called carbon dating and in this lesson we will learn what this is and how it is used. Carbon dating, or radiocarbon dating, is a method used to date materials that once exchanged carbon dioxide with the atmosphere. In the late 1940s, an American physical chemist named Willard Libby first developed a method to measure radioactivity of carbon-14, a radioactive isotope.

Raw (i.e., uncalibrated) radiocarbon ages are usually reported in radiocarbon years "Before Present" (BP), with "present" defined as CE 1950.

Such raw ages can be calibrated to give calendar dates.

But what's interesting is as soon as you die and you're not ingesting anymore plants, or breathing from the atmosphere if you are a plant, or fixing from the atmosphere. Once a plant dies, it's no longer taking in carbon dioxide from the atmosphere and turning it into new tissue. And this carbon-14 does this decay at a specific rate. And you say, hey, that bone has one half the carbon-14 of all the living things that you see right now.

And then you can use that rate to actually determine how long ago that thing must've died. It would be a pretty reasonable estimate to say, well, that thing must be 5,730 years old.

Carbon-14 has a relatively short half-life of 5,730 years, meaning that the fraction of carbon-14 in a sample is halved over the course of 5,730 years due to radioactive decay to nitrogen-14.

And carbon-14 is constantly doing this decay thing. So over the course of 5,730 years, roughly half of them will have decayed. Well, if you know that all living things have a certain proportion of carbon-14 in their tissue, as kind of part of what makes them up, and then if you were to find some bone-- let's just say find some bone right here that you dig it up on some type of archaeology dig.After plants die or are consumed by other organisms, the incorporation of all carbon isotopes, including 14C, stops.Thereafter, the concentration (fraction) of 14C declines at a fixed exponential rate due to the radioactive decay of 14C. ) Comparing the remaining 14C fraction of a sample to that expected from atmospheric 14C allows us to estimate the age of the sample.However, once the organism dies, the amount of carbon-14 steadily decreases.By measuring the amount of carbon-14 left in the organism, it's possible to work out how old it is.




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