You might remember that it was mentioned earlier that the amount of carbon-14 in living things is the same as the atmosphere.

Once they die, they stop taking in carbon-14, and the amount present starts to decrease at a constant half-life rate.

After viewing the video on carbon dating, use your newfound knowledge to: Did you know…

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Carbon dioxide in the atmosphere contains a constant amount of carbon-14, and as long as an organism is living, the amount of carbon-14 inside it is the same as the atmosphere.The half-life is always the same regardless of how many nuclei you have left, and this very useful property lies at the heart of radiocarbon dating. The graph below shows the decay curve (you may recognize it as an exponential decay) and it shows the amount, or percent, of carbon-14 remaining.You will notice that after around 40,000 years (or 8 half-lives), the amount left is starting to become very small, less than 1%.The half-life is the time required for half of the original sample of radioactive nuclei to decay.For example, if you start off with 1000 radioactive nuclei with a half-life of 10 days, you would have 500 left after 10 days; you would have 250 left after 20 days (2 half-lives); and so on.

Carbon dioxide in the atmosphere contains a constant amount of carbon-14, and as long as an organism is living, the amount of carbon-14 inside it is the same as the atmosphere.

The half-life is always the same regardless of how many nuclei you have left, and this very useful property lies at the heart of radiocarbon dating. The graph below shows the decay curve (you may recognize it as an exponential decay) and it shows the amount, or percent, of carbon-14 remaining.

You will notice that after around 40,000 years (or 8 half-lives), the amount left is starting to become very small, less than 1%.

The half-life is the time required for half of the original sample of radioactive nuclei to decay.

For example, if you start off with 1000 radioactive nuclei with a half-life of 10 days, you would have 500 left after 10 days; you would have 250 left after 20 days (2 half-lives); and so on.

This technique works well for materials up to around 50,000 years old.