Name: How Does Radiocarbon Dating Work? - Instant Egghead #28
Uploaded: 2017-02-08T01:04:39.000Z
Duration: 2 min 11 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

For people, we'd ask to see  their birth certificate.

Scientists can read it by looking at the ratio of two different types of carbon atoms.

Of course, every living thing  is made of carbon.

Plants grab carbon dioxide from the atmosphere

and use it to form  complex organic molecules.

Animals get their carbon by eating these plants.

But there's more than one form of carbon.

Most carbon atoms  have six protons and six neutrons.

High up in the atmosphere, sometimes  cosmic rays hit nitrogen atoms.

This creates carbon  with six protons and eight neutrons.

But Carbon 14 has one unique  and important attribute: it's unstable.

So once an animal dies, the Carbon 14  in its body will start to go away.

about half of the Carbon 14 atoms will decay into nitrogen.

After one half-life, the animal will have

about half the amount  of Carbon 14 it started with.

After another half-life, it will have about a quarter.

And after another half-life, it will have about an eighth.

By contrast, the amount of Carbon 12  it has in its body will stay the same.

By measuring the ratio of Carbon 14 to Carbon 12,

we can measure how many thousands of years have passed since the animal died.

Carbon dating works for fossils  up to about 60,000 years old.

For older fossils, scientists use unstable  elements that have much longer half-lives.

For Scientific American's Instant Egghead, I'm Michael Moyer.

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How Does Radiocarbon Dating Work? - Instant Egghead #28

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