The radiocarbon half-life or decay rate has been determined at 5,730 years.Next comes the question of how scientists use this knowledge to date things.

The difference in the number of sand grains represents the number of carbon-14 atoms that have decayed back to nitrogen-14 since the mammoth died. The sand grains in the top bowl fall to the bottom bowl to measure the passage of time.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 also similar to the principle behind an hourglass (figure 4).So one would think that since the radiocarbon dating method works on organic (once-living) materials, then radiocarbon could be used to date fossils.After all, we should be able to estimate how long ago a creature lived based on how much radiocarbon is left in its body. Radiocarbon (carbon-14) is a very unstable element that quickly changes into nitrogen.Because we have measured the rate at which the sand grains fall (the radiocarbon decay rate), we can then calculate how long it took those carbon-14 atoms to decay, which is how long ago the mammoth died. If all the sand grains are in the top bowl, then it takes exactly an hour for them all to fall.

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