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Carbon dating transformed fields like archeology and paleontology, but its use might be in danger.

Hosted by: Stefan Chin

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For researchers studying objects younger than 60,000 years or so, carbon dating is one of the most valuable tools out there. It involves analyzing the ratio of two kinds of carbon atoms.

And with it, scientists have figured out the ages of everything from mummies to old manuscripts. Carbon dating has transformed fields like archeology and paleontology. And it’s helped us get a much better understanding of what the world was like thousands of years ago.

The problem is, carbon dating might also be in danger, thanks to fossil fuels, of all things. The idea of carbon dating was first proposed in the 1940s, and it was important enough to win its discoverer a Nobel Prize. It relies on two kinds, or isotopes, of carbon: one called carbon-12, and another called carbon-14.

Carbon-12, or C-12 for short, is basically normal carbon. It has six protons and six neutrons, and it’s stable, so it doesn’t change and decay into different atoms over time. Carbon-14 is rarer, and it does decay.

C-14 has two extra neutrons, which makes it unstable. Over about 5730 years, half of the atoms in any sample will turn into a more stable form of nitrogen. That’s called its half life.

Carbon-14 is produced when radiation from objects like the Sun interacts with those stable nitrogen molecules as they’re floating around in Earth’s atmosphere. Then, the C-14 ends up in carbon dioxide, and works its way into plants and animals through photosynthesis and the food chain. Historically speaking, the amounts of C-12 and C-14 in the atmosphere have been roughly consistent over the years.

So scientists can expect to find a predictable ratio in most organic materials. That ratio is what carbon dating is based on. So, say researchers were trying to figure out how old some frozen animal tissue is.

If their sample has less C-14 than normal, that suggests that it’s been around long enough for that carbon to decay, so it’s older. But if they have a sample where the ratio is normal, it’s probably relatively new. By tracking exact ratio changes and knowing the half life of C-14, scientists can usually pin down an object’s age to within a few decades.

Carbon dating has worked for years, but now, there’s a problem:. That consistent carbon ratio is changing. Admittedly, it has changed before.

But those changes were small enough that they weren’t a huge deal, and the results could be easily calibrated with other measurements. Now, things are getting more dramatic. Over the years, as we’ve burned fossil fuels, we’ve launched a lot of extra carbon dioxide into the air.

And since those fossils fuels are so old, almost all of their carbon-14 has decayed. That means we’re adding a bunch of carbon-12 to the atmosphere so much that it’s really messing with the ratio that scientists use for carbon dating. Officially, this is called the Suess effect, after the scientist who first noticed this pattern in the 1950s.

And it’s not great news. According to one 2015 paper, if we keep burning fossil fuels at this rate, we’ll add so much extra C-12 to the atmosphere that new materials in 2050 will seem 1000 years old. There will be so much C-12 in them that the amount of C-14 will look tiny and decayed by comparison.

And without an outside reference, it will be almost impossible to figure out how old they really are. Many groups are already working to reduce the rate at which we burn fossil fuels and that’s good for everyone, not just archeologists. But we probably won’t stop using them completely any time soon.

Thankfully, one researcher came up with a solution to help us sort through this mess. Or at least, it’s a reliable way to tell if fossil fuels have skewed measurements. In a 2016 paper published in the journal Environmental Research Letters, he suggested we just look at a different isotope of carbon.

Carbon-13, or C-13, has just one extra neutron. And like carbon-14, it forms naturally, but it’s pretty rare. Plants don’t really store it, so there isn’t much of it in fossil fuels or in current living things.

And it only makes up 1% of the Earth’s atmosphere, so it’s also getting overshadowed by all the extra C-12 we’re putting out there. But unlike carbon-14, C-13 is stable. That means the amount in a sample should be predictable and shouldn’t change over time.

Researchers should see a constant percentage of C-13 that is, unless there’s a skewed amount of carbon-12. In his 2016 paper, this scientist suggested that researchers should always check on that C-13 percentage during the carbon dating process. If it’s unusually low, they’ll know the sample is affected by extra carbon-12, so traditional carbon dating won’t be reliable.

They’ll have to use another method. For example, if an organic object was found in a hard rock layer, researchers can estimate its age by dating the rock, which doesn’t always require carbon. Ideally, we’ll be able to stop this problem by reducing our fossil fuel usage.

But since that might not happen soon, this carbon-13 strategy will definitely be helpful. All this week, we’re turning our attention at the end of each video to a Skillshare class we think you’ll get a lot out of. We try to make them relate to the topic of the episode, which is pretty easy because there are over 20,000 classes on skillshare.

There aren’t any Skillshare classes on carbon dating though. Which, I guess isn’t too surprising. So instead, I wanted to tell you about this class taught by award-winning designer Mirko Ilić.

It’s called Making Art to Drive Change, and that still feels kind of related. Mirko Ilić is a world class artist and designer, who teaches master’s degree illustration at the School of Visual Arts in New York and runs his own studio, which is famous for its strong visual concepts. He’s captivating to listen to, and the project for the class is inspiring.

As he points out in the class, no matter what your background, everyone has something they’re passionate about and can make art. Right now Skillshare is offering SciShow viewers 2 months of access to all of their classes for free. So you could take a poster design class from an expert like this for free!

Check it out as well as any other class you like by following the link in the description. Thanks for watching and for supporting SciShow. [♩OUTRO].