Carbon dating process

The radiocarbon half-life or decay rate has been determined at 5,730 years.

carbon dating process-32

The standard way of expressing the decay rate is called the half-life.5 It’s defined as the time it takes half a given quantity of a radioactive element to decay.

So if we started with 2 million atoms of carbon-14 in our measured quantity of carbon, then the half-life of radiocarbon would be the time it takes for half, or 1 million, of those atoms to decay.

If carbon-14 has formed at a constant rate for a very long time and continually mixed into the biosphere, then the level of carbon-14 in the atmosphere should remain constant.

If the level is constant, living plants and animals should also maintain a constant carbon-14 level in them.

Instead, the radiocarbon atoms in their bodies slowly decay away, so the ratio of carbon-14 atoms to regular carbon atoms will steadily decrease over time (Figure 1c).

Let’s suppose we find a mammoth’s skull and we want to date it to determine how long ago it lived.

Since each beta particle represents one decayed carbon-14 atom, we know how many carbon-14 atoms decay during a month.

Chemists have already determined how many atoms are in a given mass of each element, such as carbon.4 So if we weigh a lump of carbon, we can calculate how many carbon atoms are in it.

We can measure in the laboratory how many carbon-14 atoms are still in the skull.

If we assume that the mammoth originally had the same number of carbon- 14 atoms in its bones as living animals do today (estimated at one carbon-14 atom for every trillion carbon-12 atoms), then, because we also know the radiocarbon decay rate, we can calculate how long ago the mammoth died. This dating method is similar to the principle behind an hourglass.6 The sand grains that originally filled the top bowl represent the carbon-14 atoms in the living mammoth just before it died.

Although many people think radiocarbon dating is used to date rocks, it is limited to dating things that contain the element carbon and were once alive (like fossils).

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