Stuff You Should Know - How Carbon-14 Dating Works

Episode Date: November 26, 2019

Some of the carbon dioxide in your body is radioactive! Don’t worry, it won’t harm you (not sure why we used an exclamation point there). Instead, it might someday be detected by future archaeologists to determine how long ago you walked the Earth. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

Hey friends, when you're staying at an Airbnb, you might be like me wondering, could my place be an Airbnb? And if it could, what could it earn? So I was pretty surprised to hear about Lisa in Manitoba, who got the idea to Airbnb the backyard guest house over childhood home. Now the extra income helps pay her mortgage. So yeah, you might not realize it, but you might have an Airbnb too. Find out what your place could be earning at airbnb.ca slash host. On the podcast, Hey Dude the 90s called, David Lasher and Christine Taylor, stars of the cult classic show, Hey Dude, bring you back to the days of slip dresses and choker necklaces.

We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it, and now we're calling on all of our friends to come back and relive it. Listen to Hey Dude the 90s called on the iHeart radio app, Apple podcasts, or wherever you get your podcasts. Hey San Francisco, we want to get back to our city by the bay. So we are this January. That's right, man. We're going back to sketch fest. It's become an annual deal for us there at the Castro Theater, always some of the best audiences of the year. You are our peeps

and we love coming to see you. So get your tickets to see us at the Castro. What day are we there? We're going to be there Saturday, January 18th. That's right, for a prime time show. Yep. So go to sysklive.com and follow the links to get information and tickets. We'll see you guys in January. Welcome to Stuff You Should Know, a production of iHeart Radio's How Stuff Works. Hey, and welcome to the podcast. I'm Josh Clark. There's Charles W. Chuck Bryant over

there. There's Jerry right there just laughing it up. Yeah. This is Stuff You Should Know, the Jokes or Jerry edition. Dent Science edition, AKA Chuck Die Slowly Inside edition. Dude, no, it's not. You're going to do just fine. This is all so intuitive. It's wonderful. I'm not worried about not doing fine, but thanks for the research. Sure. Well then, I'm really excited about this if you know that.

I think you're going to do fine. You are going to as well. I'm going to see to it. I think Jerry's going to do great. Jerry, how are you doing over there? Okay. She's pressing buttons like I've never seen her press buttons. Stop doing that. I wonder what kind of weird sound effects just happened after touching all those buttons.

Don't you hurry. Jerry just laughed. I don't know if the mic picked that up. All right, everybody's like, okay, you're officially stalling now. Jerry's a quiet laughter though. You ever notice that? It's all nose. Yeah, she's all nose. This is Jerry laughing hard. There's some serious ASMR triggering going on right now.

Yeah, that's right. There's a little bit of snot on the microphone cover. All right. Carbon 14 dating. It works sort of the end. Yeah, it's not the worst description of it ever. We can do better than that though. Yes. Luckily, you did a great job with this, but I also, my advice to anyone, if you don't understand a science thing, and you're an adult, just don't worry about what anyone behind you thinks.

Just looking at your laptop and you go to the most rudimentary children's science website you can find. Yeah. And that always helps. There is no shame in that. No shame. Because seriously, the people who write those websites are probably some of the best science explainers on the planet.

Sure. Yeah. And they know how to really just not dumb it down because kids are smart, but you know. That's funny. You flip flopped on kids apparently. You mean stupid kids? Yeah. You always said they were dumb until just now, so good for you, Chuck. We're all over the map. Well, I feel like we're really growing up these days.

So Carbon 14, for those of you who don't know, is this really clever scientific method where you can actually kind of look inside of a material and figure out how much Carbon 14 is in there. And in doing so, you can actually tell how old it is or at least how long ago it was since the thing you're dating was alive. Yes. And it is a comparative, well, there's another word for that. What's it called?

Relative dating. Yeah, relative dating. I guess comparative isn't the worst word. Right. Especially if you're talking about literature. Right. Because what they're doing is comparing it to things that are alive today. And because of all the gobbledygook we're about to talk about, that equals a pretty good

estimate. And then from there, there are even further things that one can do if one were so inclined as a scientist. And there are a lot of people who are inclined to do this. This is a very exciting, energetic field of science right now. Like if you want to jump into an ever-evolving, constantly moving BA field. BA Boracus field kind of science, start studying radiocarbon dating. Yeah, actually it wouldn't be a BA Boracus field because didn't that stand for bad attitude?

Did it? I think so, right? Oh, no one in radiocarbon dating has a bad attitude. No, but they are BAs. Right. But you're right, it is ever-evolving and they're constantly looking for better ways to pinpoint more accurate timelines on things. So it's not like a job you're going to get in and be like, oh, this whole thing again.

Right, no, no. And it's just like they're constantly filling in blanks and stuff like that. It's just, it's good work. So what they're looking for, the people who do radiocarbon dating, is carbon-14, which I said, and that is radiocarbon. It's called that because it's a radioactive form of carbon. That's right. And it's everywhere on earth.

It's just all over the place. It's part of the carbon cycle and it's part of the web of life, but it starts out way up in outer space as a cosmic ray. That's right. Should we give the basis definition before we jump to the ins and outs? Of radiocarbon dating? Yeah. I mean, I think like the most rudimentary definition might help some people out.

But like you said, carbon-14 is everywhere, including inside us because it's in plants via photosynthesis and we eat plants and animals eat plants. Some people eat animals. And because of that, it's kind of an every living thing. And carbon-14 dies away very slowly. And because we know this and because we know it happens predictably, then we can measure that in a sample and then compare it, like I said, to something living. And then you do a little math, ipso facto, it's probably an ipso facto, is it?

Presto change-o? Yeah, presto change-o. Bada bing, bada bing, bonjovi, what was that? Bada bing, bada boom, bonjovi. That was yours. Was it? Yeah. Oh man.

You came up with that on a carousel at Zoo Atlanta in about 2012. That's right. That's where that's carbon dated to, that joke. But because we know that, we can compare it to something that's alive today. And then with a little math, we can figure out the rough estimate of how old it is. Yeah. I mean, that's radio carbon dating in a nutshell for sure. That's right.

But like you said, it starts out as cosmic rays way out in outer space. Right. And so a cosmic ray, we're not entirely certain where they come from, but they're super high energy particles, usually like pieces of atoms that are just shooting toward Earth and throughout outer space at incredible speeds, and when they encounter the atmosphere, they start running into the atoms that make up the atmosphere. And because these particles are so high energy, these cosmic rays, when they smack into atoms and other particles and molecules and all that, they just burst them apart.

Not just burst like an atom into like its protons and neutrons, it'll tear apart a neutron like it's nothing. It actually creates other high energy particles like muons, pions, x-rays. What else? Zaxons. Is that right? No. That was a video game.

Was it? Zaxon? Yeah. Sure. It was a good one. With a Z? Yeah. I think it was ZA double XON.

If I'm not mistaken. I am not familiar with that. It was in Atari. Oh, okay. It was in a stand-up game? Oh, actually it may have been, but I played it on Atari. Because I could see a kid in a kiss t-shirt playing that game stand-up in an arcade. Yes.

It sounds like that kind of game. That would have been me had I not been deathly afraid of kiss. I'll bet. Because they were devil. Well, they were knights in Satan's service, obviously. That's right. Yeah. Okay, so all these muons, x-rays, pions, all that stuff, there's one other little particle

that can be created when a cosmic ray collides with an atom, and that is a neutron, a high energy neutron, right? That's right. Okay. So what's happening now is a chain reaction because cosmic rays are bombarding the atmosphere. That's right. And what can happen is they can get really pushy if a high energy neutron collides with, let's say, a nitrogen-14 atom, they'll get real pushy and they'll just knock the proton

off and move right in there and say, this is my house now. Right. And that was once a stable atom, nitrogen-14, which had seven protons and seven neutrons. Seven each. Is now an unstable atom with six protons and eight neutrons. And now it's no longer nitrogen-14. What you have, fella, is carbon-14. Yes.

An unstable, meaning radioactive, but not radioactive, meaning scary and dangerous. No. And this means that it's in a higher energy state and it's temporary, eventually wants to decay back into that nitrogen-14 state. Yes. And it does that. Yeah. Eventually, it's sometimes spontaneously, sometimes down the road, that neutron will turn back

into a proton, which sounds like magic until you realize that atoms and all of the particles that make up atoms are really just vibrations of energy, and it can temporarily go to a higher energy state or a lower energy state, and that is how something would change from like a high energy neutron back to a proton. Right. And you said that carbon-14 is everywhere, which is true, but that doesn't mean there's like tons and tons of it relative to carbon-14, or wait, carbon-12. Yes.

There's a lot more carbon-12. Right. So carbon-12 is the stable version of carbon, and it's way more abundant than carbon-14. Carbon-14 is kind of like a freak, a monster that gets made accidentally, and is extremely rare even though there's a ton of it, but compared to carbon-12, it's very rare. Something like one carbon-14 atom for every trillion carbon atoms, that's pretty rare, but it also gives us a ratio, Chuck, and this is a big initial point. Yeah.

And like you mentioned before too, or maybe I said it, this is part of the carbon cycle so it's inside all the plants, and the animals are eating the plants, we're eating plants, some people eat animals, so it's inside all of us, and it's everywhere. But that ratio is really important because like we said, it starts to decrease because it craves homeostasis and wants to get back to its former life as a stable particle. Right. As a stable boy. Stable boy.

Yeah. You can brush that horse. And it would be an atom because it's going from a carbon-14 atom to a nitrogen-14 atom. Right. But that ratio is important because as it dies away, there are going to be fewer and fewer carbon-14 atoms with that dead organism over time, whereas if something is alive, it has that steady amount and that's where the comparison comes in. Right.

So, as far as a plant or you or a dog or anything living is concerned, there's no difference whatsoever between a carbon-14 molecule of carbon dioxide and a carbon-12 molecule of carbon dioxide. Yeah. I mean, it sounds hard to digest because we said it's radioactive, but there really is no difference as far as we're concerned. Right. It basically takes a human scientist to analyze it using an extremely sophisticated machine

to be able to tell the difference. That's right. So, that means that when it does come down out of the atmosphere, it's spewed out by a volcano or something like that, it just becomes part of the food chain like any other atom of carbon that's locked in with oxygen to form carbon dioxide. So, as you're living, like you were saying, you're constantly taking it in. You're constantly eating. It's just a part of life as a carbon-14 and carbon-12.

Right. But when you die, you stop taking in carbon of all kinds. And all of a sudden, a clock is set because of that decay of carbon-14. That's right. And that decay, like we said, it happens spontaneously and atom might suddenly convert from carbon-14 to nitrogen-14. You can't predict when that's going to happen because of the uncertainty that's part of quantum physics, right?

But if you have a large enough sample, then you can start to predict when X number or X percentage of that sample of carbon-14 will have spontaneously changed from carbon-14 to nitrogen-14, and that's called the half-life, which is everyone has heard of. That's half-life. That's just standard stuff. Yeah. I think everyone has heard of half-life and I bet 90% of the people that know that term don't really fully grasp it.

Well, yeah. It's just the amount of time it takes for half of the radioactive atoms in any given sample to convert back into a stable form. Yeah. That's it. It's pretty easy. And we know in this case, the half-life, and we'll get to how we figured all this out, but the half-life of carbon-14 is 5,730 years.

If you keep going, it goes to a quarter life, then I guess an eighth. Yeah, it just keeps going. So if you have 100 carbon-14 atoms, if you come visit it in 5,730 years, you're going to find you have 50. And if you visit it in another 5,730 years, you're going to have 25, and then 12 and a half or 13, maybe. I don't know. And it just keeps going until there's ultimately none left over a long enough stretch of time,

which is with carbon-14 like 50 or 60,000 years. Yeah, I saw 60,000 mostly, but then I think it can get a little hinky at 50. So 50 to 60 is pretty good. And I think it gets hinky at this point because of the equipment we're using to measure it. I think as our equipment gets more and more sensitive, that time will go further and further out, because as long as you have two atoms, you should still be able to measure them. Or even one, probably, I'm not going to go out on a limb for that one, but I'm going to caveat that with a probably.

Okay. Well, let's take a little break here, and we're going to come back here in a second and talk about the very smart dude who figured all this stuff out quite a few years ago. Hey, friends. When you're staying at an Airbnb, you might be like me wondering, could my place be an Airbnb? And if it could, what could it earn? So I was pretty surprised to hear about Lisa in Manitoba, who got the idea to Airbnb the

Backyard Guest House over childhood home. Now the extra income helps pay her mortgage. So yeah, you might not realize it, but you might have an Airbnb too. Find out what your place could be earning at airbnb.ca slash host. On the podcast, HeyDude the 90s called David Lasher and Christine Taylor, stars of the cult classic show HeyDude, bring you back to the days of slip dresses and choker necklaces. We're going to use HeyDude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s.

We lived it, and now we're calling on all of our friends to come back and relive it. It's a podcast packed with interviews, co-stars, friends, and non-stop references to the best decade ever. Do you remember going to Blockbuster? Do you remember Nintendo 64? Do you remember getting frosted tips? Was that a cereal? No, it was hair.

Do you remember AOL Instant Messenger and the dial-up sound like poltergeist? So leave a code on your best friend's beeper, because you'll want to be there when the nostalgia starts flowing. Each episode will rival the feeling of taking out the cartridge from your Game Boy, blowing on it and popping it back in as we take you back to the 90s. Listen to HeyDude the 90s called on the iHeart radio app, Apple podcasts, or wherever you get your podcasts. All right, Chuck, just to recap real quick, because I think this episode bears it, okay?

You've got Carbon-14. It's part of the food chain. You take it in as you're living. When you die, you stop taking it in, and so those Carbon-14 atoms start to decay, which means that if you compare the dead organism to a living organism, and the ratio of Carbon-14 to Carbon-12 in the dead organism compared to the living organism, you'd be able to tell how long ago the dead organism was alive and taking in more Carbon. That's the basis of radiocarbon dating.

That's right. So that is, we have a man to thank from the University of Chicago named Willard Libby. That's a great name. I heard his name was Wildman or Wild Bill. Wildman Willard Libby? Yeah. Because he's just crazy? I guess.

He must have been a party animal. Who knows? You don't get a nickname like Wild Bill for nothing. They don't go around handing those out to just anybody. Yeah, not even just figuring out Carbon-14 dating. You wouldn't get a Wildman for that. No, no, no. Like even Chris Farley wasn't called Wild Bill.

No. I think Willard Libby had a side gig. Yeah. You know? But he was the party monster. Maybe at the University of Chicago in the 1940s, perhaps. So he figured out how Carbon-14 worked and how it could be used to do this. Before we were even positive, science even knew for a fact that there was such a thing

as Carbon-14. That's pretty impressive. And in fact, in 1946, it was just a few short years after we had discovered Cosmic Rays. So he was really on the leading edge of science. Yeah. You know? Right.

He was like, these particles, we're not even sure they exist. But if they do, we could figure out how to use them to date dead organisms. And he won a Nobel Prize in 1960 for this. I think rightfully so. And chemistry, yeah, for sure. Even though, as we'll see, he got a few things wrong. Oh, yeah. And the one thing that's kind of tough to wrap your head around here is he, and this

is, it just is what it is at this point, I think, but he selected 1950. The year 1950 is year zero for his experimentation. And he compared all the samples against this, and that is still what we do today. We didn't revise a lot of this stuff. It's interesting. No. They definitely are like, okay, I think the reason why is because by the time it started become sophisticated and more refined, so many samples had gone through that.

It's like, we're just going to stick with this for now, okay? Yeah. It's really interesting. So 1950, when you're radiocarbon dating an object, that is year zero. So anytime you get a date back, which we'll talk about, it's actually saying, this is how long before 1950, this thing was last alive. Right. And we're not talking, it just, it doesn't have to be like a plant fossil because we

said carbon is in virtually everything. So a leather belt comes from a cow. That cow ate the plant. What else? Wooden ships. Wooden. Fabric. Yeah.

We find poop, of course, old poop, old alcohol, old beer, because of yeast. There are many, many, many things, obviously bodies, oatsie, our pal. Yeah. As long as whatever you are dating was at one point alive, which means it wasn't a rock or a mineral from birth, you can date it. You should be able to date it as long as it's about 50 or 60,000 years or younger. Yeah, but there was a problem early on in this process because you needed a lot of this material to basically destroy, to find out how old it is.

And people didn't want to give up these great finds. Like I found a skull and they're like, well, can we destroy that skull to find out how old it is? And, you know, they would turn around and say, no, it's my skull. Right. And radio carbon researcher was saying, like, I was just asking to be pleasant, give me that skull. Yeah, but then you would say, no, it's my skull and I'm just happy to call it old.

Right. And then Willard Libby would step in and just do like a pile driver on the guy with the skull. That's why I got the name. Yeah. He would just come in and crush people. Yeah. He'd be hiding maybe in another room in back or something and just pounce.

And someone would go, cuckoo. Yeah. He would swarm. But here's the thing, we've gotten a lot better over time. The equipment has gotten a lot better, more sophisticated. So we don't need that much now and people are giving up their finds because you can have a little gram of bone from the skull and I think everything will be okay. Yeah.

And so because of that, like it's gotten way more common to radio carbon date stuff. I read in the UK, they really started dating everything they found because the UK passed a law that said if you're a developer and you turn up any sort of archeological evidence on like one of your buildings or developments, you have to pay to have it dated. And so like it started to kind of get the burden for paying for it was shifted to industry. And so it started to really blow up and that helped kind of push the technology along and help lower the expense and increase the sophistication of the machines that were being used. Wow.

Yeah. It's pretty neat how that happens. Well, here's what you got to do if you're going to start out this process is you got to really clean your sample very well, otherwise it's going to, it can mess up everything and not just the tests that you're making. If you have what's called a hot sample, which means you didn't clean it well enough for its contaminated. A gram of hot sample.

You can destroy a lab basically to the point where they'll just have to shut down for weeks or even months to get everything right and everything in there might be destroyed. Like yeah, all the other samples that may be super valuable. My skull. Yeah. You know. Sorry. So it's a big deal if something isn't cleaned right because it really throws everything off

and can ruin everything else. But once you do have it cleaned, when you date it, there's few different methods that you can use. But the one that I saw is the most common is actually turning that carbon based sample into carbon graphite like pure carbon. And then you take that little piece of pure carbon that you've just created and you shoot a beam of energy through it. A lot of energy.

Yeah. Like 2 million volts. Which is a lot. Not all at once. I think they ramp it up, don't they? Yeah, over time. But at some point it's got, it's been accelerated to 2 million volts of energy. Right.

Okay. And then so once you have this thing, basically a particle, a mini particle accelerator, it's passed through a spectrometer, which can actually measure the different masses of the atoms in this beam that you've shot through the graphite. That's right. It's detecting the little bits of carbon. Yeah. That's pretty impressive stuff.

Yeah. I mean, this is the kind, this is the level of technology we're at right now in 2019 and this has been around since like the 80s or 90s. Yeah. Just think of what's coming next. What did they use before the spectrometer? They used something called... Between 50 and 80.

Data counting and it was clunky and expensive and not nearly as reliable, but basically what it did was something different where it would sit there and study a piece of graphite or gas. They often gasify stuff to pure gas and then it would just like shoot a beam through it and study. I think a beam, it would somehow study the sample for days maybe and it would count the number of atoms that had spontaneously converted from carbon 14 to carbon 12 and then it would do a little mathematic rigmarole and say, at this rate of decay, this is how old this

organism is. Well, thank goodness we have the spectrometer now then because it's much more precise and faster. It sounds more futuristic to you. Yeah. Mass spectrometers. Yeah. So, you're going to shoot this beam, you're going to throw it in the wonder machine,

actually not the wonder machine, we've already taken that for something else. Yeah, it's a thoughtless piece of graphite. And then you compare that ratio to the, again, year zero, which is the ratio in 1950, which is still a little confusing. Oh yeah, it's clunky. It is very clunky. And then that difference basically, like we've said eight times now, shows how many years have passed to produce the amount of decay in that sample.

So if you took like a sample of wood from an old ship, an old boat you found out, right? Or how? That's the new right, by the way. Did you say route? Yeah. Okay. And you analyze it and you found that based on the amount of carbon-14 in there, it was something like it dated to like 845 BCE.

Okay. Okay. You'd be like, great, now we know where this ship is from. But if you tried to go out and publish a study with that, hopefully your radiocarbon colleagues would be like, whoa, whoa, whoa. Yeah. There's a few more steps involved here. You're new here.

And that's like the most precise radiocarbon date anyone would have ever given. You'll be laughed out of the field if you do this. Yes, don't do that. Instead, there's a couple of things that you have to do first. So radiocarbon dates are given as a span of time. Sure. Bit of a range. So it'll say, and also because it's comparing to 1950, it's given not as a date like BCE

or AD or CE or anything like that, it's BP before present, years before present. That's right. So for that piece of wood, say you would actually get something like 2,715 years before present, plus or minus 30 years. So is it always 30 or is it? No, no. It can depend. It can range dramatically.

Like Uzi, they have them down to about 300 or 350 years. And the shorter the span of time, the plus or minus years or the window of years that you get, the less confidence you have. So maybe you'll have like 26% confidence that it's from 845 BCE to 855 BCE, but you have 95% confidence that there's like this 200 year span, it's somewhere in there. That makes sense because I have a million percent confidence that it's somewhere within the last 18 million years. Exactly.

Right? So it just keeps the larger the window, the more confident you are. But I mean still you're talking 100, 200 years depending on how old the sample is, how good the sample is. Yes. So it's still pretty, they can zero it in pretty well. And that science's job is to not say, well, let's just make a really big range and that'll be good enough.

They want to zero in as much as possible and still be accurate. So the thing is though is if you do the math and you say, well, wait a minute. On your example? Yeah. So 715 years before present, plus or minus 30 years gives you a range of between 726 and 666 BCE. But that's not even close to what you said. Yeah.

Which was 845 before. Right? That's right. Yeah. So why wouldn't 845 be in the sample? Chuck. Well, because like we said in the very first sentence, radiocarbon dating is not super, I mean, it's accurate on a wide range, but it's a little clunky.

It is. Part of it is because there's actual problems, like known problems built in to the actual process of radiocarbon dating and the results that they get back. Should we take another break? I'll bet that pause I just had sounded really long in the replay. Probably so. Felt like it. But yeah, let's take a break, man.

We'll come right back and talk about more science right after this. Hey, friends, when you're staying at an Airbnb, you might be like me wondering, could my place be an Airbnb? And if it could, what could it earn? So I was pretty surprised to hear about Lisa in Manitoba, who got the idea to Airbnb the backyard guest house over childhood home. Now the extra income helps pay her mortgage. So yeah, you might not realize it, but you might have an Airbnb too.

Find out what your place could be earning at airbnb.ca slash host. On the podcast, Hey Dude the 90s called David Lasher and Christine Taylor, stars of the co-classic show Hey Dude, bring you back to the days of slip dresses and choker necklaces. We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it, and now we're calling on all of our friends to come back and relive it. It's a podcast packed with interviews, co-stars, friends, and non-stop references to the best decade ever.

Do you remember going to Blockbuster? Do you remember Nintendo 64? Do you remember getting frosted tips? Was that a cereal? No, it was hair. Do you remember AOL Instant Messenger and the dial-up sound like poltergeist? So leave a code on your best friend's beeper, because you'll want to be there when the nostalgia starts flowing.

Each episode will rival the feeling of taking out the cartridge from your Game Boy, blowing on it and popping it back in as we take you back to the 90s. Listen to Hey Dude, the 90s called on the iHeart radio app, Apple Podcasts, or wherever you get your podcasts. So I thought this was, was this from How Stuff Works? And you, in your brain? Yeah, and a bunch of other places too, sure. And you, in your brain?

Sure. Okay. But there's an interesting thing to note here, which is science makes a lot of assumptions when it comes to dating stuff. And this is the best way to say it. If you find, like if they find like a leather shield that they dig out of an archaeological site, they get super excited and they can date the shield and they can say, or they probably will say, well, whoever this heroic person was in the battlefield died around

this date because that's where the shield is dated from. But that is not necessarily true because they're dating the shield from the cow skin that's on the handle, let's say. And that just says when that cow was alive last, has nothing to do with when this person made the shield, how long that leather had been around before they went out onto the battlefield and took an arrow to the forehead? Yeah, maybe they were like super into vintage leather to use on their shield handle. It sounds ridiculous, but it's totally possible.

But the thing is is archaeology is based on making assumptions and presumptions based on the context. And it's like, this is totally fine, this is widely accepted, this is not new or scandalous at all. But like that is part of archaeology's job is to say, here's the context of this find. And based on this radiocarbon date of this, it's a pretty good guess that they killed the cow, made the leather, made the shield, and then the guy died probably within a 10-15 year window.

Sure. I mean, the idea, it would be an even weirder assumption to think that it was an ancient hipster who collected old, old leathers. Right. Check out my new one. That's right. And then the other part of it too is they also use it to compare to other stuff. Like if they're in a pit filled with other soldiers from a certain nation or clan or

whatever, and they knew of a lost grave, they may have found that if it kind of roughly correlates to the date they were thinking. Like there's a lot of stuff that they put together. They don't just say, here's what the radiocarbon date says, so this is what it is. That's right. So because science does this, Libby was certainly doing this, the wild man was doing this, and he was making assumptions. And he was, and hey, we're not knocking the guy because you want a Nobel Prize for this.

But he assumed a couple of things that were not correct. One of which was he got the half-life wrong. He said the half-life of carbon-14 was 5,568 years. So close. We actually know it's 5730, like we said. And he also presumed that carbon-14 in the atmosphere is very steady over time. And it's something we can really depend on, like they're being a certain amount. Yeah.

And that's not really the case either. No, it's not. And that second one's a big one. Like the first one, you can just mess around with some math and be like, oh, okay, well, this is the actual half-life. Well, but it's interesting. That's what we've had to do because that's another thing we didn't go back and change. Because it was all done on the basis of 5568.

Right, right. So the initial stuff, the initial dates that were done when Libby invented it were based on a half-life of 5568. From 1950. Right. But I don't know exactly when they figured it out, but at some point in the ensuing decades, they figured out, no, the half-life is actually 5730. And rather than just go back and re-analyze the old samples, which actually may have been

destroyed by this time, they said, we're just going to stick with this convention and follow it. We're going to do some math and just say, actually, this is the real half-life, convert it to the Libby half-life, and then have a radiocarbon date. Yeah, but the other thing you got wrong, like you said, is the bigger problem because it can't just be solved with math. And that is his presumption that carbon-14 in the upper atmosphere has produced at a steady rate.

We know now that there are all kinds of things that can and have affected that rate over the years, everything from ocean currents to supervolcanoes to solar flares to the Earth's magnetic field, it has fluctuated a lot over time. Yeah. I mean, from year to year, we're starting to find that it's not at all steady. And that's a big one because one of the foundations of radiocarbon dating is this idea that it's like a reliable clock that just starts clicking backwards. That's right.

At any point in time, whatever year you come in on, you're going to be able to compare it to a modern sample and get a coherent radiocarbon date that will make sense. That's just absolutely not the case because of all of those fluctuations. That's something that this field is definitely grappling with, which it will be able to overcome and largely has already because they use other types of dating to calibrate their radiocarbon dates. Yeah, which is really cool. We were talking about the relative dating of carbon-14 dating.

What they're now trying to do, well, not now, they've been doing it for a while, is absolute dating like what you're talking about, comparing it to known quantities. And one of those is tree rings. Yeah. And I'm surprised, we've talked about tree rings a little bit here and there, but I wonder if it could be a shorty on its own, at least, maybe more. We'll just start rapping on it and whether if it turns into a real deal episode, we'll go with it.

Yeah. We'll just cancel our dinner plans and just keep going. But tree ring dating is called dendocrinology, counting tree rings, and not all trees have tree rings. We'll get to that, which can be a problem. But a lot of them do and some of them grow every year, just like you've learned and everyone probably thinks is true from like kids science class. Right.

So once a year, a tree has a ring. So if you cut a tree down, you can just count the rings and know how old it is. Which is, I mean, basically right, depending on the tree. Exactly. But here's the thing is trees absorb that carbon-14, just like everything else, but those tree rings don't. Once they have completed a tree ring cycle, that tree ring is essentially dead inside the tree and is not accepting anymore carbon-14.

Yeah. It's like a fossil. It's like if you look at the outside of a tree, that's the living part. Like as big as a tree is and enormous as it is, the actual living part of it is just this outside veneer and like the leaves and everything, right? Yeah, I guess so. Everything inside is what used to be outside, but is now inside. That's right.

Because a new ring of growth grew around it. So since it's not taking in any more carbon, it's like a snapshot of the carbon-14 that was in the atmosphere the year that tree ring grew. Yes. And we know this. And now we have something to compare against those carbon-14 data results. Yeah. Because if you chop the tree down today, you would say, thank you, Father Tree, Mother Tree,

for sacrificing your life for science, that's what you have to say first. And you start counting the tree rings backwards. If you get to another tree that's much older, but that lived, or the lifetime of which overlapped with the tree you just cut down, you can eventually jump over from the tree you just cut down to this older tree and keep counting backwards. And then just keep, if you find enough old trees, keep leaping from tree to tree, counting tree rings as if it was one big old tree. That's really cool.

It is. And there are very, very old trees that do exist on earth that you can count backwards from over very long spans of time, but you can also use multiple trees. Yeah. And like, if you're sitting at home or in your car thinking, well, why don't they just find the oldest tree and go there? Like you want that overlap because you want a complete record because stuff you're dating might fall in that, they need everything to fall in that range.

And so this has been extremely helpful for radiocarbon dating because they have managed to compile basically a library of tree ring data going back like 14,500 years. It's amazing. It's called the Holocene Tree Record. And it's one of the, I didn't even know it existed. Now I'm just, I love it. Yeah. So I want to, I like want a bound copy of it just for the coffee table or something.

And lay in a hammock in the middle of Pando and read it and read it and be like, oh, look at this year, Pando. What do you think? What happened this year? And Pando would hug you. So I was trying to think of something you would do back to Pando, but I would go blow on Pando's leaves. I bet that feels good.

Sure. There are other places in nature that have these same kind of snapshots if you wanted more than, because you need more just than the Holocene Tree Record. They can use coral reef because there's clearly carbon in the ocean, stalactites and stalagmites, which are called speliothems. If anyone ever bust that out at a party, you'll know what they're talking about. Just back away slowly. Yeah.

You probably should. Because everyone else is just going to be talking about, I can never remember which ones are which. Exactly. I mean, speliothems, just let me educate you. Goodbye. They are made of carbon and they are deposited in layers, just like the tree rings in the coral.

In fact, they have found some in China, kind of recently, that go back 54,000 years. Yeah. I think they really recently found this, so much so that it hasn't been fully vetted, but they were super excited about it, that the idea that it gave basically a long, mineral-rich tree ring library of 54,000 years of the carbon-14 concentrations of the atmosphere. That's awesome. If it does pan out, that would be amazing. What's the deal with the lake in Japan?

It reliably puts down a new layer of sediment every six months. That's pretty cool. Yeah. They've taken core samples and in these core samples, they've turned up leaves trapped in single layers in something like 650 different spots. So all they have to do is count backwards, they'll know the year that this leaf is trapped in. It's like the tree rings.

And then test the carbon-14 in the leaf and you've got a picture right there. And that is called, what we'll call, a library of atmospheric carbon-14 concentrations. Yeah. They should have a name. It does. It's called INT-Cal. Okay. And there's different programs that you can run all this through.

Before back in the 40s and 50s, they were, I guess, using slide rules and stuff like this to come up with these. Now we have basically machine learning algorithms running these computations for us, but they have programs that use this calibration library to basically say, here is what the radiocarbon data is saying, what does this library of absolute dates say? And then what they do is they actually, well, the computer, I should say, overlaps what's called the wiggles. And they hold it up to the light.

Yeah. And they find where these kind of wiggles overlap, which are confidence intervals, I guess. And where it's most confident that you have a pretty good idea of what the range is for the age of this sample. And that means we know exactly how old everything is always, right? I mean, precisely to the day. That is not true. Because all the things we just mentioned, the speleothems, the coral, everything has

its own individual problems. Coral, it turns out, isn't a great material for calibrating this stuff because ocean concentrations of carbon are not the same as in the atmosphere. So that kind of throws it off right there. It does. So if you're comparing something that lived on land to coral in the library, in Cal Library, yeah, it's not going to calibrate very well. Tree rings are a problem too because they figured out that depending on the hemisphere

that the tree grew in, it will give you a different atmospheric concentration. Because the southern atmosphere has more oceans and those oceans absorb more carbon dioxide. So there's actually less carbon-14 on land in the southern hemisphere than there is in the northern hemisphere. So if you checked out a waterlogged oak that grew in Ireland in 1082 CE, if you found a coyote tree in New Zealand that grew that same year, they would have different radiocarbon dates because they have different radiocarbon concentrations. So there's a lot of things confounding this stuff that's keeping it from being less precise.

That's right. And it gets even worse because there have been long stretches of time on earth in our history where carbon-14 production really increased every year over hundreds of thousands of years or tens of thousands. Yeah. Well, there are stretches. So all over the radiocarbon calendar, there are these things called plateaus. And I think the longest that they've ever found is a few hundred years.

When I said tens of thousands. Yeah, it was a lot. Just like a radiocarbon date. All right. I don't feel so bad. They found this thing called the Hallstatt Plateau. More like the Hallstatt Disaster. Yeah, that's what some people call it.

Am I right? I'm sure that's what Willard Libby called that. Sure. But basically, there were periods during Earth's history. This one in particular goes from 760 to 420 BCE, where the production of carbon-14 in the atmosphere just increased basically steadily every year. So nothing ever got older relative to new stuff, which means that if you radiocarbon date something in 760 BCE and something in 420 BCE, they're going to give you the same

exact radiocarbon date. 420, huh? Does that make sense? 420. That was your response? 420, huh? Hey, there's people out there thinking it. To the Hallstatt Disaster.

All right. Willard Libby would be proud. He was the wild man. So while this is important, it's not just to put a date on something so we know how old it is and we can just put it down in a museum or a history book or whatever. It really opens up all of science and all of ancient history to interpretation and kind of rocked the world about a lot of things that we thought were true that aren't true. Yeah.

They call it the radiocarbon revolution and like for good reason really, yeah. Well, one good example is in the UK there, we've talked about Stonehenge. They used to think that Stonehenge was the result of the, how do you pronounce that? Mycenae, mycenae, I don't know. Mycenae? You'd think I'd know, mycenae. I think it's the mycenae, civilization in Greece. But the A and the E on the end, it's got to do something more than, like why not just

add a Y instead of an E? Hey, I'm with you. And you know, sometimes you see the A and the E together conjoined. Sure. Like Ronnie and Donnie Galleon, you know? Wow. So what is that? I don't know.

It's a stone thing. So we used to think that came from an ancient Greek civilization. But because of radiocarbon dating, they said, no, no, no, no. This is, we had the age all wrong and Stonehenge came before that ever happened, before the civilization was even there. So it really helps clear up a picture of everything from Otsi the Iceman to knowing that the Shroud of Turin was only 700 years old. So it can confirm things and it can quash other things.

Right. And then, and the way that they used to do it before was they would just kind of dig in the earth and turn up artifacts. And because an artifact was closer to the ground than another one, it just meant it was more recent. That's like as precise as they could get. Radiocarbon was like, not only are we going to do that, but get this pal, here's a date and a pretty good estimate of a date that this thing existed.

That's how much it changed things. They used to be like, this is older than this. Now it's this Otsi the Iceman was running around, you know, in 3300 BCE. And in doing that, it also changes everything in that they're saying, oh, well, Otsi was also found with tattoos on them that seemed to suggest acupuncture, which apparently they didn't think anymore, but that changed our idea of how old acupuncture was. And then he had certain tools on him. We didn't know that they were making these tools back then, but now that we've reliably

dated Otsi, we know that this tool making complex is much older. People had professions much sooner than we thought. It just opens up everything when you have a date for one thing. Yeah, the Tenderles are far reaching. Right, exactly. And broad. And actually here in the United States, too, in North America, you know, we did a whole episode on the Clovis police.

Oh, sure. The Clovis. The idea that the Clovis people were the first Americans and they came over from crossing over the, I guess, the Bering Land Bridge when the ice sheet receded. And so Willard Libby did a test that showed there was no way that the ice sheet was open anywhere before 12,000 to 15,000 years ago. So he actually set a baseline. This is when the earliest people possibly could have been here.

Well, we've been finding and radiocarbon dating settlements that are older than that. They found one in Idaho on the Snake River. I can't remember the name of the island. That's like almost 16,000 years old. And it shows definitively that since the ice sheet was there, they couldn't have come over on the Bering Land Bridge. So now we think the first Americans came over by boat. That's right.

All because of radiocarbon dating. Amazing. But we're screwing it all up for the future because of human activity that, you know, we're burning a lot of fossil fuels and we were releasing a lot of carbon into the atmosphere. And so much so that that consistent, previously reliable ratio of carbon 12 to carbon 14 has been knocked all out of whack because of us. And in the next, what, 30 years, 30 to 40 years, we may not be able to date things accurately using this method anymore.

Yeah. Yeah. Because when, you know, when they say, well, you burn fossil fuels, you release a lot of carbon dioxide, well, those fuels used to be alive. So they used to have carbon 14 in them, but they're so old, there isn't any carbon 14. Now it's all just carbon 12. And we're releasing tons of carbon 12 into the atmosphere that wouldn't normally be there. That's right.

And nuclear tests that we conducted had a big, actually had the opposite effect. Between 1955 and 1963, the concentration of carbon 14 in the atmosphere doubled, almost doubled. Yeah. So there's all screwy now. It is a very screwy. So much so that now they have modern samples. They have a beat harvest from the seventies that they used to replace a beat from France

from 1950 that they used to be like, this is the baseline now for modern. This is what we're reduced to is sampling beats for God's sake. That's how much it screwed things up. I love beats. But they have figured out how to use this kind of modern screwiness to also date recent remains, which everyone thought was just impossible, that you couldn't tell when a body lived or died if it were just a decade or so dead or less. But we have historical records for all this stuff.

I know it's a big deal, and we're screwing stuff up to the future, but isn't the utility of carbon 14 dating because it was prehistory? Yeah. That certainly helps. And yeah, I guess you're right, that having a record would definitely help quite a bit. And I'm not saying who cares then, but at least we have that going for us. That's a good point. It'd be like, well, the leather seat from this automobile is the same age as this leather

shoe from 3,000 years before, which is which. Right. But yeah, they have figured out how to use it for forensics based on your teeth enamel, which are like tree rings, and then based on your soft tissues. But your soft tissues degrade so they figured out that they can actually test the casings from the larva that eat your soft tissues as you're decomposing. So the soft tissue is the carbon 14 in this scenario? Yeah, which you're constantly remaking.

And then as you die, it stops being taken in and then starts decaying. And as you're being eaten by these bug larvae, they shed their casings, and the casings don't degrade. So you can come along and test the casings, and they ate your carbon 14, and you can figure out when that person, that body, last lived based on the casings of the bugs that ate it. And in a million years, if I were not to get cremated and they were to bury me into the ground, the only thing that would remain of me are the three titanium screws holding

in my three fake teeth. That's neat. A million years. Who'd have thought? Yeah, there he is. Yeah. There's Chuck. One, two, three.

You got anything else? There may be more than that by then too. Right. I don't have anything else. So anything else? You want to keep going? I've got nothing else. We can keep talking about this.

I don't have no dinner plans. Okay. Well, I think we're going to stop with carbon 14. We don't want to press our luck. It did go pretty well, Chuck. I told you. I think so. And since I said it went pretty well, it's time for Listener Mail.

All right. I was preparing for the next episode. Yeah, we got Listener Mail first. Look at me. All right. I'm going to call this a soup follow-up. If you remember, we talked about canned soup in a previous episode on what else? Augmented reality.

All right. And I think we were pegged as a progresso guys because you spoke up first with a name brand. Right. I'm a Campbell's man. Hey, I don't discriminate. I like Campbell's chunky too. I just kind of went along with it.

I didn't want to ruffle any feathers. Okay. I didn't speak up. But this is about that. Hey guys, there are no words to describe how much I enjoy your podcast. I've listened to every single episode and continue to do so each and every week. Thank you for bringing wonderful science exploration for knowledge and laughs to my days. So far so good.

I listened to the latest episode on augmented reality while on a plane to Boston and I could not stop laughing when you got to a full-on tangent about canned soup. I thought this is my moment. This is my chance to ride in. I've been two-star struck before, but here we go. I know canned soup all too well. I spent seven years right out of college working for General Mills. Yes, they make the cereal, but they also own Progresso.

I worked in sales managing our businesses with our East Coast and National Accounts. Three years ago, I left General Mills and went to work for Campbell's soup. Oh, it's like a do-you-some-poom over here. I guess so. Just outside of Philadelphia, I guess you could say, I too have a thing for canned soup. I currently manage our soup and prego business and one of our largest East Coast grocery chains and although it doesn't seem complicated, I can tell you a lot of work goes in to you enjoying your can of red and white chicken noodle soup.

I still love that. Campbell's chicken noodle. Oh, yeah. So good. It's like, how do you mess with a classic like that? Not a butt. There's also Progresso creamy chicken noodle, which is the bomb. When you mentioned this episode brought to you by Progresso as a joke, I was just waiting

for you to plug that. You liked Campbell's as well and even more. Ha-ha. Either way, I'm just glad you both enjoy eating our soups. I would be happy to give you a tour of Campbell's soup HQ if you're ever in Philly. Thanks to the entire team for all you do. You guys are a legend. Combined into a singular.

That's from Kathleen. And Kathleen, no shade to Progresso, but I'm a Campbell's man. I eat three soups. A day? No. I eat Campbell's chicken noodle. Uh-huh. A chicken corn chowder.

I don't know if I've had that. That's so good. And I eat their New England clam chowder. Yeah, that's good. Who eats Manhattan clam chowder? I don't know. Or I'm sorry, Manhattan clam chowder. No one.

Not even Manhattan. They're like, get this away. Give me the real stuff. Yeah. Give me that creamy goodness. Do you ever have a meatball alphabet? No. I don't know what we're in those meatballs, but I grew up on them.

And look at me now. I know. That's all the soups I eat though. I have three soups. Yeah. And you don't do the chunky stuff? Campbell's chunky? I mean...

They come in large cans. It's like a hungry man version of... Well, that's the chicken corn chowder and the... I have had that. And it's good. Those are chunky. Have you ever had the chicken pot pie? No, but I just made a homemade gluten-free chicken pot pie biscuit topped.

How do you make a biscuit without gluten? You make it with one-to-one flour instead of wheat flour. What kind of flour is not wheat flour? What? Is like the white flour, the wheat flour... Have you never heard of gluten-free pasta? No. I mean, I've heard of it.

I haven't eaten it. It's just made with flour without gluten. It's called one-to-one as in the ratio. Oh, I see. I got you. So basically, you buy the gluten-free flour. Sometimes it's rice flour, tapioca, but... Have you had chickpea flour?

I don't think so. It's not bad. I mean, I'm not gluten-free. I did this so Emily could enjoy chicken pot pie. Sure. So you make the little biscuits and you lay them on top of your pot pie and then you brush it with egg yolk and then it bronzes up to a shiny brown top. People laying on the beach in Rio.

So good. That is nice, man. Yeah, make a good chicken pot pie. Have you had it already? Is it at home already? Yeah, I had it this past weekend. Nice. But I have not had the soup, which is what led me to that tangent.

It's good. I won't... I don't discriminate. Progresso, Campbell's, it's all good. And Chuck is checking his phone to see what time it is, so I guess we should probably end this episode. If you want to get in touch with us to offer us a tour of where you work, that's always nice.

Thank you. You can go on to StuffYouShouldKnow.com, check out our social links, or you can send us an email to StuffPodcasts at iHeartRadio.com. Stuff You Should Know is a production of iHeartRadio's How Stuff Works. For more podcasts from iHeartRadio, visit the iHeartRadio app. Apple podcasts are wherever you listen to your favorite shows. On the podcast, Hey Dude, the 90s called, David Lasher and Christine Taylor, stars of the cult classic show Hey Dude, bring you back to the days of slip dresses and choker necklaces.

We're going to use Hey Dude as our jumping off point, but we are going to unpack and dive back into the decade of the 90s. We lived it and now we're calling on all of our friends to come back and relive it. Listen to Hey Dude, the 90s called on the iHeartRadio app, Apple podcasts or wherever you get your podcasts. Hey, I'm Lance Bass, host of the new iHeart podcast, Frosted Tips with Lance Bass. Do you ever think to yourself, what advice would Lance Bass and my favorite boy bands give me in this situation?

If you do, you've come to the right place because I'm here to help and a different hot sexy teen crush boy bander each week to guide you through life. Tell everybody, everybody about my new podcast and make sure to listen so we'll never ever have to say bye, bye, bye. Listen to Frosted Tips with Lance Bass on the iHeartRadio app, Apple podcasts or wherever you listen to podcasts.