Rerun: Is Carbon Dating on the way out?

are really gonna dig. But that doesn't help me today, does it. So instead of a news episode, we're going to have a little bit of a classic episode here. I thought, because I'm feeling so very old as I try to to make sure I have these episodes ready for you guys, it would be good to kind of take stock. And by that I mean we're going to listen to a classic episode called is carbon Dating on the Way Out? This episode originally published on August two

thousand and fifteen. I hope you enjoy. This comes from nikkil Cardale, and I do apologize that I'm sure I mispronounced your name. The request was, could you do an episode explaining this carbon dating is pretty useful, So this effect seems relevant and uh Cardale actually uh commented on and and included another tweet from real scientists that included an article titled will our fossil use ruin our ability

to use carbon dating as a scientific tool? This is really fascinating the idea of using carbon dating, uh, and how that that method might be in jeopardy because the use of fossil fuels. So I thought I would go into that explain what carbon dating is and why it might not be an accurate means of telling how old something is after too long. So going into the article, it's about how the enormous amount of carbon emissions we generate could make carbon dating and unreliable means to determine

the age of certain types of materials. But to understand how that's possible, we need to know how carbon dating works first, So we're gonna do a carbon dating one oh one. Now, the first thing that we have to talk about is carbon fourteen. So the fourteen in carbon fourteen tells us it's an isotope of carbon. This particular isotope must have eight neutrons because carbon has six protons. You can change the number of neutrons in an atom.

That's the different types of isotopes atoms may have. But you can't change the number of protons and atom has without changing that element. So carbon had six protons, and if you change that number of protons, you change the element itself. It acts reacts differently in chemical operations, and uh is no longer carbon. So carbon twelve is the most common form of carbon that we find. It has

six protons and six neutrons. Then you have carbon thirteen, which is six protons and seven neutrons, and both of those are stable forms of carbon. That means they don't decay. So if you have carbon twelve or carbon thirteen, you put it in a box and you leave for I don't know, two billion years, and you come back, you're still gonna have carbon twelve or carbon thirteen because they remain stable. They do not decay. But carbon fourteen is different.

It is a radio isotope. Radioisotopes are also known as radio nucleides, and these are isotopes of a particular atom that have an unstable nucleus. These isotopes undergo what we call nuclear decay, and in that process they release some excess energy in the form of stuff like gamma rays and or subatomic particles. Carbon fourteen undergoes what is called beta decay. So when it decays, one of the neutrons in the nucleus spontaneously changes into a proton, an electron,

and an anti neutrino. The nucleus gives the boot to the electron and the anti neutrino, but the proton stays behind, which means the atom no longer is a carbon atom. Since again we mentioned that atoms depend upon the number of protons and the nucleus, so the carbon fourteen decays into nitrogen fourteen, and nitrogen fourteen has seven protons and

seven neutrons. Also, by the way, one of the few stable elements that has both an odd number of protons and an odd number of neutrons uh, and nitrogen fourteen is stable. It makes up the vast majority of the nitrogen found naturally under Earth, More than of the nitrogen found on Earth is nitrogen fourteen. So radioactive decay occurs naturally within these isotopes, and it's a spontaneous occurrence. That's really important to remember. Carbon fourteen has a radioactive half

life of about five thousand, seven hundred years. There's some confusion about what that means. I find in day to day conversations with people who haven't had science in a while. You guys who have recently had this in science class, you're rolling your eyes right now. But for adults who have not taken a science class in a long time, this might require some some refreshing. So, half life of

five thousand, seven hundred years, what does that mean? It means if you have a given amount of carbon fourteen, after five thousand, seven hundred years or so, you'll have only half of that carbon fourteen remaining, the other half having undergone decay, radioactive decay and turning into nitrogen. Now, this doesn't mean that all the carbon four team will be gone after another five thousand, seven hundred years, nor doesn't mean that carbon fourteen has a full life of

eleven thousand, four hundred years or anything like that. In fact, what it really means is that after another five thousand, seven hundred years, half of the remaining sample will have decayed, leaving you with about a quarter of what you started with. And another five thousand, seven hundred years if that means you be left with about an eighth of that sample, and so on. Carbon fourteen exists naturally on Earth in trace amounts. Before the nineteen forties, the carbon fourteen on

Earth was created through a natural process. Once in a while, cosmic rays, these very high energy particles in outer space, would collide with an atom in our atmosphere or upper atmosphere, and this collision would end up emitting a high energy neutron that then could collide with nitrogen atoms that are also way up there in our atmosphere. Now, cosmic rays

are high energy sub atomic particles. They originate outside of our solar system, usually are admitted by supernova of massive stars, and these sub atomic particles are primarily atomic nuclei and high energy protons. So this collision of the high energy neutron with the nitrogen forces a proton to leave the nucleus and the in fourteen changes to C fourteen. So, in other words, nitrogen fourteen turns to carbon fourteen. So instead of having seven protons and seven neutrons, the new

atom has six protons and eight neutrons. The proton that was broken off from the nucleus zooms off with an electron, so you get one proton and one electron. That means you have an atom of hydrogen. So again what's happening is a high energy neutron collides with nitrogen fourteen, forces out a proton. The proton and an electron high tail it and honeymoon off as hydrogen and the incoming neutron

joins the party, and now you've got carbon fourteen. So pre nineteen forties, carbon fourteen is rare because of two reasons. It undergoes radioactive decay, so over time it disappears, and it's produced by an event that's not super frequent, though it's also not uncommon, so it does happen regularly enough that carbon fourteen is replenished, but it's a very small overall percentage of the carbon here on Earth. We've got some more to say about carbon dating in just a second,

but first let's take a quick break for our sponsor. Now, living things here on Earth absorb carbon through various means, and some of that carbon is carbon fourteen. So it maybe that you know, you eat a plant in that

plant has some of the carbon fourteen in it. Now you have some of the carbon fourteen and you and if we know the ratio of carbon fourteen to the stable form of carbon twelve, we can look at materials and analyze them to see how the ratio of carbon fourteen to carbon twelve in the material stacks up to the standard ratio. With living things, this becomes a matter of looking at how much carbon fourteen is not there?

All right, That's it's a little confusing. Let me explain. So, when a living thing is still alive, it accumulates carbon at about the same rate it loses carbon, so carbon cosmic rays produced this carbon fourteen frequently enough that the ratio between carbon fourteen and carbon twelve remains steady, So the percentage of carbon fourteen to carbon twelve is fairly standardized.

But when a living thing stops being alive and turns into a not living anymore thing, it stops accumulating carbon, so it has the carbon that it has inside of it stays. That's it. You're not losing anymore. You're not gaining any more except for carbon fourteen because carbon fourteen undergoes radioactive decay, so over time, some of that carbon

fourteen starts to convert to nitrogen. So that means if you can look at the remains of a living thing and detect the ratio of carbon fourteen to carbon twelve. You can get an idea of how long ago it was that it stopped taking in carbon, as in, how long ago was it that this lip, once living thing died. It gets a little more complicated than all that, but here's the basic rule. If we want to be really precise, here's the equation we use to determine the age of

a sample of material. You have an equation where you take the natural logarithm of n F divided by n o uh that in turn is divided by negative point six nine three, and then you multiply it by t uh one half, so one half t the natural logarithm is a specific logarithm applied to this equation and other

things as well. N F divided and oh actually refers to the percentage of carbon fourteen and the sample compared to the amount found in living stuff today at times one half is the half life of carbon, so that's five thousand, seven hundred years. So it was a lot easier to understand this if we take a specific example.

So let's say you've got a sample of some sort of material and you have determined that there is five percent of the amount of carbon fourteen in that material compared to what you would find in something that is alive. Right now, so you take a sample of a living thing, and then you take the sample of the thing you're testing. You see that the thing you're testing only has five percent of the carbon fourteen you would find in living things.

That means you would fill out the equation with the natural logarithm of point zero five divided by negative point six nine three, and you multiply that that result to with five thousand, seven hundred years. The natural lug ay them at point zero five, by the way, in case you don't want to whip out your calculator, is negative two point nine nine five seven three to two seven three five five. If you divide that by negative point six nine three, you get four point three to two

eight four five. Don't dial that number. If you take that number, the four point three, etcetera, and you multiply that by five thousand, seven hundred years, you end up with twenty four thousand, six hundred forty point two years. I mean, the stuff you're looking at died somewhere around that time frame, give or take thirty two hundred years, So somewhere on twenty four thousand, six hundred forty years ago is when that thing no longer breathed or lived,

or however you wanted to find it. By the way, this approach does have a limitation. Anything older than sixty

thousand years is pretty much out of bounds. Carbon fourteen just isn't a reliable means of dating that sort of material, and we have to rely on other methods so and fourteen because of the decay once against two very small amounts, it's very difficult to narrow it down to a specific time, and if it's long enough, there won't be any carbon fourteen at all all the carbon fourteen will have decayed by then. You can't use carbon dating if there's no

carbon fourteen left. So to actually test the carbon fourteen concentration, you first have to take the sample, uh whatever object it might be. You have to remove part of it, and typically you would apply some chemicals to the material, usually a very strong acid wash and a strong base wash. That's to remove all the contaminating materials that could end

up giving you false readings on carbon fourteen. Then you would burn the sample within a glass container to capture the carbon dioxide that is emitted when you burn the material. And then you would analyze the carbon dioxide to find out the concentration of carbon fourteen. So you can see that this approach has a big drawback. It ends up damaging whatever it is you are attempting to date in

the first place. And that's why some particularly high valued items go without being tested, because the perception is that even a small sample of that original piece would be too much damage to to uh make on this item. So certain items are considered very precious and there's a big resistance to using carbon dating because by definition, you're going to be damaging the material. Now, there's several lines of research they're exploring possible non destructive means of using

radiocarbon dating. There's one that uses plasma oxidation and the use of non destructive washes to clean samples of those contaminating humic acids, which would lead to errors if they remain behind. But those are still largely in the testing

phase and aren't the common means of using carbon dating. Also, keep in mind that we use this method to estimate the date of things made from organic materials, like the Dead Sea scrolls, but this estimation is based upon when the materials were harvested So, in other words, whenever the living thing that the materials came from stopped being alive, it doesn't tell us the date of when the artifact

was actually produced. So it's possible that you could come across an artifact like a scroll, and you use carbon dating on it and find out that the scroll material is two thousand years old, meaning two thousand years ago whatever the scroll was made out of stopped living, But it doesn't tell you about the contents written in the scroll. It's possible that the contents were added to the scroll

much after the living thing stopped being alive. Still, it's a pretty good bet that the two are within the same neighborhood of time, rather than someone held onto blank scrolls for a few centuries before finally jotting something down. All right, it's all this is cool, But how did we even figure out radio Carbon dating would be a

possible way of figuring out how old something is. Well, some early discoveries were made in the nineteen thirties at the Lawrence Radiation Laboratory in Berkeley, and you probably remember that if you've been listening to tech stuff. It factored heavily into the discussion I had with Ben Boland about the Manhattan Project. So Franz Curry, an American physicist, observed something really interesting when he irradiated a cloud of air

in a cloud chamber. He used neutrons to UH to irradiate that cloud, and he saw proton recoil tracks that indicated something was losing protons. So he concluded that the neutrons that he was using were colliding with nitrogen fourteen and producing what was believed to be a form of carbon as a result, with hydrogen being the other product of this collision. His work was further explored by physicists like Tom W. Bonner, W. M. Brubaker, W. J. Burcham,

and Maurice gold Hauber. Now collectively, this laid the foundation for the simple equation of a high energy neutron plus nitrogen fourteen produces one hydrogen atom and one carbon fourteen atom. Then you had Narrico Fermi. We talked about him in the Manhattan Project, and his work showed that the cross section of a nitrogen fourteen atom was much larger than other materials, and that suggested that neutron and nitrogen collisions might happen fairly regularly in nature as long as there

were a supply of high energy neutrons. All right, we got a little bit more about carbon dating, and then what's It's back to reality for me? I guess so Sage Korff, who was a physicist who was born in Finland and whose family immigrated to the United States in the early twentieth century, he discovered the phenomenon that cosmic rays interact with atoms and produce high energy neutrons in the upper atmosphere. So Pharem's prediction and course observation, we're

starting to kind of coalesce here. The observations convinced scientists that the neutrons themselves were not cosmic rays, because the neutrons had a lifespan of just eighteen minutes, and therefore a neutron wouldn't be able to survive the long trip through space. They must have been something else first, so they said the neutrons had to be a byproduct of another interaction. A cosmic ray must be interacting with something

in the atmosphere. That interaction caused this high energy neutron to be emitted, and Quarter hypothesized that these neutrons could then interact with nitrogen fourteen to produce carbon fourteen in the upper atmosphere. Now, it was Willard F. Libby who came up with the idea that since carbon fourteen is generated at a steady rate due to cosmic ray interactions in our atmosphere, you should be able to use it

to measure how long something has been dead. Libby would measure the value of carbon fourteen's half life at five thousand, five hundred sixty eight years, give or take thirty years, which became known as the Libby half life. And Libby himself would be awarded the Nobel Prize in nineteen sixty for his work in radiocarbon dating. All right, so that's the history of radiocarbon dating and generally how radiocarbon dating works. So why is it in trouble or what could possibly

be causing confusion with radiocarbon dating. Well, there are two big things we need to talk about, and one was one that I've alluded to a couple of times. I mentioned that, you know, pre nineteen forties, you had a certain level of carbon fourteen that was pretty standard, but the nuclear age really messed things up for us. They made carbon fourteen dating a bit tricky. Starting in the

nineteen forties, we began testing nuclear bombs. Now, these bombs released a lot of energy upon exploding, partly in the form of high energy neutrons. You could probably see where this is going. Some of those high energy neutrons ended up interacting with night jan fourteen atoms, which meant that it produced carbon fourteen atoms as a result. So the concentration of carbon fourteen increased in the wake of nuclear

bomb testing. So anything that died after the nineteen forties actually has a higher concentration of carbon fourteen than the stuff that died before the nineteen forties did even at the time of death. According to Professor Nalini nod Karnie of the Evergreen State College, the nineteen fifties saw a one hundred percent spike in carbon fourteen coming into the atmosphere.

In nineteen sixty three, the United States and Russia agreed to stop above ground nuclear testing, and the levels of carbon fourteen in the atmosphere gradually dropped down to their normal levels. But that means there's a blip in the carbon fourteen radar between the nineteen forties and nineteen sixty three. So if you put yourself in the shoes of a future archaeologist. Radio carbon dating becomes unreliable because the levels

of carbon fourteen could be decept tip. If the thing you're measuring died during the era of nuclear testing, it might appear to be younger than you thought because there's a higher concentration of carbon fourteen in its sample than you otherwise would have expected. So it may seem that something died in twenty fifteen as opposed to nineteen sixty three. That's just an example. Now to the article that prompted this episode in the first place, that's a different case.

Researchers published a study in the Proceedings of the National Academy of Sciences about how the use of fossil fuels is further making radiocarbon dating less reliable, and this time it's not an excess of carbon fourteen. It's actually the opposite problem. Fossil fuels have no carbon fourteen in them because they are fossil fuels. This is billions of years old, so they're far too old for any carbon fourteen to remain.

Remember that carbon fourteen is decaying over time and turning into nitrogen, so eventually all of those carbon fourteen atoms decay. So burning a fossil fuel create releases carbon dioxide, and the carbon in that CEO two has no carbon fourteen and it's all carbon twolve carbon thirteen. So the more fossil fuels we burn, the more we dilute the concentration of carbon fourteen that's in the atmosphere. So stuff from the nuclear age tends to look younger than it really

is because of the higher concentration of carbon fourteen. Stuff from the later ages of fossil fuel use will look older than they really are because carbon fourteen has been diluted. So, according to the study, fresh organic material in twenty fifty would contain the same amount of carbon fourteen relative to carbon twelve as something dating from ten fifty. So you have a thousand years of doubt in any radio carbon

dated samples. You would look at the two samples if you if all you had were miniscule samples of two things and one of them was a T shirt that was made in and another was a piece of cloth that dated from ten fifty, and you did radiocarbon dating,

you'd get the same result. This is not good if you are trying to figure out how old something is Heather Graven, who authored the study on fossil fuel emissions and the effect on radiocarbon dating, says that if we were to reduce carbon dioxide emissions drastically in the very near future, the effect on future radiocarbon dating would be equivalent to inserting a one year error on top of any estimation. If we don't drastically reduce emissions, that error

range will continue to grow over time. One thing that the concentration of carbon fourteen tells us is how much carbon dioxide in the atmosphere comes from the burning of fossil fuels. So as we see the concentration decrease, we know that's because proportionally more carbon twelve is being released into the atmosphere, diluting the already tiny concentration of carbon fourteen. So that's useful for scientists who are studying climate change

and pollution. That's not exactly a happy story, is it. So what are our options if carbon dating becomes unreliable, Well, that depends on what you're trying to analyze. If you're looking at inorganic stuff like rocks, you don't need to use carbon fourteen in the first place. That would be pretty much useless. You would use something else like potassium argon dating, which is useful to estimate the age of rocks that are a hundred thousand years old or younger.

And if that's not a big enough range, you can actually use uranium lead dating, and that will let you estimate rocks between one point four and five million years old. There's a lot of different options if you're trying to date stuff. When it comes to organic materials, however, it's a lot more tricky. Radio carbon was a great tool, but if it becomes unreliable, we're gonna have to use other methods like contextual clues and other items that are helping us connect things to dates. So this is a

big problem. I guess you could argue that's a big problem for future generations and perhaps the records we leave behind now are so uh so complete, they're so voluminous, I guess is the best word. That future generations will likely have more than enough material to determine when something originated from our time versus earlier times. But the point being that the way we're interacting with our world is changing.

This fundamental ratio of carbon fourteen to carbon twelve, and that means that a really brilliant means of determining how old something is is not really going to be an accurate measure for very much longer. So it's kind of a bummer. Obviously for things that are much much much older. UH will at least in the short term, not be that big of a deal, especially if we can relate it to other items that we we already know the age of those items. It won't be as destructive as

saying we can never use radio carbon dating again. We just have to keep that changing ratio of carbon fourteen to carbon twelve in mind so that we make sure we're making accurate measurements. I hope you enjoyed that classic episode of tech Stuff. Again, my apologies. I've got a lot of things I wish I could have talked about, like the fact that there's now a patent for a retractable lightsaber blade thing. I really want to talk more

about that, so maybe next week. But in the meantime, if you have any suggestions for topics I should tackle on tech Stuff, let me know. Send me a message on Twitter. The handle is text stuff h s W. I'll talk to you again really soon. Yeah. Text stuff is an I heart radio production For more podcasts from I heart Radio, visit the i heart Radio app, Apple podcasts, or wherever you listen to your favorite shows.