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Posted by / 14-May-2018 10:43

History of carbon dating

By measuring the ratio of the radio isotope to non-radioactive carbon, the amount of carbon-14 decay can be worked out, thereby giving an age for the specimen in question.

But that assumes that the amount of carbon-14 in the atmosphere was constant — any variation would speed up or slow down the clock.

Two distinct sediment layers have formed in the lake every summer and winter over tens of thousands of years.

The researchers collected roughly 70-metre core samples from the lake and painstakingly counted the layers to come up with a direct record stretching back 52,000 years.

Various geologic, atmospheric and solar processes can influence atmospheric carbon-14 levels.

Since the 1960s, scientists have started accounting for the variations by calibrating the clock against the known ages of tree rings.

The technique hinges on carbon-14, a radioactive isotope of the element that, unlike other more stable forms of carbon, decays away at a steady rate.

Organisms capture a certain amount of carbon-14 from the atmosphere when they are alive.

Bronk Ramsey’s team aimed to fill this gap by using sediment from bed of Lake Suigetsu, west of Tokyo.

For example, all carbon atoms have 6 protons, all atoms of nitrogen have 7 protons, and all oxygen atoms have 8 protons.

The number of neutrons in the nucleus can vary in any given type of atom.

The illustration below shows the three isotopes of carbon.

Some isotopes of certain elements are unstable; they can spontaneously change into another kind of atom in a process called “radioactive decay.” Since this process presently happens at a known measured rate, scientists attempt to use it like a “clock” to tell how long ago a rock or fossil formed.

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The clock was initially calibrated by dating objects of known age such as Egyptian mummies and bread from Pompeii; work that won Willard Libby the 1960 Nobel Prize in Chemistry.

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