Science.

Carbon-14 and other radioisotopes are used to measure the age of fossils, rocks, and other materials that make up Earth's geologic history. These techniques are reliable and valid. They provide clues into our earliest origins. And they contribute to the hundreds of lines of evidence supporting Charles Darwin's theory of evolution, which continues to stand the test of time.

To learn more, watch the video above and read the transcript below. And don't forget to leave a comment at the bottom of the page. Talk nerdy to me!

One of the ways that researchers measure the age of organic material is through carbon-14 dating. In 1960, Willard Libby won a Nobel Prize for developing this technology. See, all living things contain carbon, which has six protons and six neutrons, so in its typical form, we call it carbon-12. But at any given time, there are trace amounts of carbon-14, or C14, in the atmosphere. C14 is a radioactive isotope that's made when cosmic rays bombard nitrogen atoms at high altitudes, converting them to this excited form.

When some living things, like plants and algae, make their own food through photosynthesis, they take in carbon dioxide from the air. Trace amounts of C14 make up a tiny percentage of that carbon dioxide, and it's integrated into the tissues of the organism. Then creatures that can't make their own food through photosynthesis (like us) eat the ones that can, and that C14 is taken into our bodies as well. And because there's a constant quantity of C14 in the atmosphere, there's a constant, corresponding quantity of it in the bodies of all living things, at least while they're still alive.

C14 is radioactive. That doesn't mean it's dangerous, only that it's unstable. Over time, it decays back into nitrogen. See, when an organism dies, it stops taking in carbon. And the C14 in the organism's tissues starts to decay at a precise speed, but the amount of carbon-12 stays the same, since it's not radioactive.

We know that it takes 5,730 years for half of the C14 in a sample to decay. It takes another 5,730 years for half of what's left to decay, and so on. This is C14's half-life. All radioactive isotopes have one. And if we compare the amount of C14 in a dead thing to the amount of regular carbon-12, voila! We can find out how old it is.

Critics also like to point out that over time, the amount of C14 in the Earth's atmosphere may have varied. But scientists know this, so they make corresponding adjustments to their measurements. And radioisotope dating may be one of the more sophisticated methods we use to know the age of fossils, but it's not the only one.

Millions of fossils have been pulled from the earth. And by the 1800s, we realized that consistently and predictably, older rock is found below younger rock, and older fossils are found below younger ones within that rock. With age comes progress: younger things are more complex, more diversified.

When Charles Darwin published "On the Origin of Species" in 1859, he didn't have all the answers. We still don't. But I can tell you this for certain: evolution is a fact. Man never walked with dinosaurs and you and I are apes. Scientific advances are made every day in hundreds of disparate fields. And not one of these findings has served to undermine the theory of evolution. Not one. Not a single fossil discovery has been out of place, on the wrong continent or in the wrong rock. There's no complexity that's irreducible and no form that was intelligently designed. The data simply don't support it. And that's the greatest thing about evolution: it just is. And it'll keep on happening whether you believe in it or not.

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