WEBVTT - Rerun: Is Carbon Dating on the way out? 0:00:04.400 --> 0:00:07.800 Welcome to tech Stuff, a production from my Heart Radio. 0:00:12.000 --> 0:00:14.600 Hey there, and welcome to tex Stuff. I'm your host, 0:00:14.800 --> 0:00:18.280 Jonathan Strickland. I'm an executive producer with I Heart Radio, 0:00:18.320 --> 0:00:21.760 and I love all things tech and typically I would 0:00:21.800 --> 0:00:26.160 have a news episode for you on today, which is Thursday, 0:00:26.239 --> 0:00:31.400 April twenty one, but this week got away from the 0:00:31.560 --> 0:00:35.240 big time. On the bright side, we have a really 0:00:35.400 --> 0:00:40.320 cool thing coming up early next month that um tech 0:00:40.320 --> 0:00:42.640 Stuff is taking part in that I think you guys 0:00:42.680 --> 0:00:47.239 are really gonna dig. But that doesn't help me today, 0:00:47.400 --> 0:00:50.800 does it. So instead of a news episode, we're going 0:00:50.840 --> 0:00:53.880 to have a little bit of a classic episode here. 0:00:54.280 --> 0:00:57.640 I thought, because I'm feeling so very old as I 0:00:57.680 --> 0:01:01.160 try to to make sure I have these episodes ready 0:01:01.200 --> 0:01:03.600 for you guys, it would be good to kind of 0:01:03.640 --> 0:01:06.160 take stock. And by that I mean we're going to 0:01:06.240 --> 0:01:10.679 listen to a classic episode called is carbon Dating on 0:01:10.720 --> 0:01:15.880 the Way Out? This episode originally published on August two 0:01:15.959 --> 0:01:21.039 thousand and fifteen. I hope you enjoy. This comes from 0:01:21.200 --> 0:01:25.120 nikkil Cardale, and I do apologize that I'm sure I 0:01:25.360 --> 0:01:28.360 mispronounced your name. The request was, could you do an 0:01:28.360 --> 0:01:32.160 episode explaining this carbon dating is pretty useful, So this 0:01:32.200 --> 0:01:38.840 effect seems relevant and uh Cardale actually uh commented on 0:01:39.000 --> 0:01:43.280 and and included another tweet from real scientists that included 0:01:43.319 --> 0:01:47.000 an article titled will our fossil use ruin our ability 0:01:47.080 --> 0:01:50.600 to use carbon dating as a scientific tool? This is 0:01:50.640 --> 0:01:54.480 really fascinating the idea of using carbon dating, uh, and 0:01:54.760 --> 0:02:00.160 how that that method might be in jeopardy because the 0:02:00.240 --> 0:02:03.040 use of fossil fuels. So I thought I would go 0:02:03.040 --> 0:02:06.920 into that explain what carbon dating is and why it 0:02:07.040 --> 0:02:10.280 might not be an accurate means of telling how old 0:02:10.320 --> 0:02:14.799 something is after too long. So going into the article, 0:02:14.919 --> 0:02:17.560 it's about how the enormous amount of carbon emissions we 0:02:17.600 --> 0:02:20.880 generate could make carbon dating and unreliable means to determine 0:02:20.880 --> 0:02:24.400 the age of certain types of materials. But to understand 0:02:24.440 --> 0:02:27.760 how that's possible, we need to know how carbon dating 0:02:27.880 --> 0:02:32.000 works first, So we're gonna do a carbon dating one 0:02:32.040 --> 0:02:34.560 oh one. Now, the first thing that we have to 0:02:34.560 --> 0:02:39.680 talk about is carbon fourteen. So the fourteen in carbon 0:02:39.720 --> 0:02:43.760 fourteen tells us it's an isotope of carbon. This particular 0:02:43.800 --> 0:02:48.079 isotope must have eight neutrons because carbon has six protons. 0:02:48.680 --> 0:02:51.360 You can change the number of neutrons in an atom. 0:02:51.440 --> 0:02:54.960 That's the different types of isotopes atoms may have. But 0:02:55.040 --> 0:02:57.880 you can't change the number of protons and atom has 0:02:57.919 --> 0:03:01.440 without changing that element. So carbon had six protons, and 0:03:01.480 --> 0:03:03.520 if you change that number of protons, you change the 0:03:03.560 --> 0:03:08.639 element itself. It acts reacts differently in chemical operations, and 0:03:09.000 --> 0:03:13.560 uh is no longer carbon. So carbon twelve is the 0:03:13.600 --> 0:03:17.360 most common form of carbon that we find. It has 0:03:17.400 --> 0:03:20.520 six protons and six neutrons. Then you have carbon thirteen, 0:03:20.520 --> 0:03:23.160 which is six protons and seven neutrons, and both of 0:03:23.160 --> 0:03:27.360 those are stable forms of carbon. That means they don't decay. 0:03:27.520 --> 0:03:30.560 So if you have carbon twelve or carbon thirteen, you 0:03:30.680 --> 0:03:33.160 put it in a box and you leave for I 0:03:33.200 --> 0:03:36.200 don't know, two billion years, and you come back, you're 0:03:36.200 --> 0:03:39.280 still gonna have carbon twelve or carbon thirteen because they 0:03:39.280 --> 0:03:43.200 remain stable. They do not decay. But carbon fourteen is different. 0:03:43.520 --> 0:03:48.839 It is a radio isotope. Radioisotopes are also known as 0:03:49.040 --> 0:03:53.640 radio nucleides, and these are isotopes of a particular atom 0:03:53.760 --> 0:03:57.880 that have an unstable nucleus. These isotopes undergo what we 0:03:57.960 --> 0:04:01.400 call nuclear decay, and in that process they release some 0:04:01.520 --> 0:04:05.280 excess energy in the form of stuff like gamma rays 0:04:05.320 --> 0:04:09.920 and or subatomic particles. Carbon fourteen undergoes what is called 0:04:10.320 --> 0:04:14.440 beta decay. So when it decays, one of the neutrons 0:04:14.440 --> 0:04:18.880 in the nucleus spontaneously changes into a proton, an electron, 0:04:19.240 --> 0:04:23.120 and an anti neutrino. The nucleus gives the boot to 0:04:23.160 --> 0:04:27.000 the electron and the anti neutrino, but the proton stays behind, 0:04:27.080 --> 0:04:30.440 which means the atom no longer is a carbon atom. 0:04:30.480 --> 0:04:33.679 Since again we mentioned that atoms depend upon the number 0:04:33.680 --> 0:04:37.480 of protons and the nucleus, so the carbon fourteen decays 0:04:37.560 --> 0:04:43.279 into nitrogen fourteen, and nitrogen fourteen has seven protons and 0:04:43.400 --> 0:04:46.400 seven neutrons. Also, by the way, one of the few 0:04:46.640 --> 0:04:50.480 stable elements that has both an odd number of protons 0:04:50.560 --> 0:04:54.839 and an odd number of neutrons uh, and nitrogen fourteen 0:04:55.000 --> 0:04:58.200 is stable. It makes up the vast majority of the 0:04:58.279 --> 0:05:02.680 nitrogen found naturally under Earth, More than of the nitrogen 0:05:02.720 --> 0:05:06.839 found on Earth is nitrogen fourteen. So radioactive decay occurs 0:05:07.000 --> 0:05:11.080 naturally within these isotopes, and it's a spontaneous occurrence. That's 0:05:11.120 --> 0:05:14.760 really important to remember. Carbon fourteen has a radioactive half 0:05:14.800 --> 0:05:19.400 life of about five thousand, seven hundred years. There's some 0:05:19.440 --> 0:05:22.159 confusion about what that means. I find in day to 0:05:22.240 --> 0:05:25.119 day conversations with people who haven't had science in a while. 0:05:25.360 --> 0:05:28.359 You guys who have recently had this in science class, 0:05:28.400 --> 0:05:31.040 you're rolling your eyes right now. But for adults who 0:05:31.080 --> 0:05:33.600 have not taken a science class in a long time, 0:05:33.960 --> 0:05:38.400 this might require some some refreshing. So, half life of 0:05:38.440 --> 0:05:41.760 five thousand, seven hundred years, what does that mean? It 0:05:41.800 --> 0:05:44.720 means if you have a given amount of carbon fourteen, 0:05:45.320 --> 0:05:49.120 after five thousand, seven hundred years or so, you'll have 0:05:49.480 --> 0:05:52.839 only half of that carbon fourteen remaining, the other half 0:05:53.000 --> 0:05:58.000 having undergone decay, radioactive decay and turning into nitrogen. Now, 0:05:58.040 --> 0:06:00.440 this doesn't mean that all the carbon four team will 0:06:00.440 --> 0:06:03.400 be gone after another five thousand, seven hundred years, nor 0:06:03.720 --> 0:06:06.880 doesn't mean that carbon fourteen has a full life of 0:06:06.920 --> 0:06:10.119 eleven thousand, four hundred years or anything like that. In fact, 0:06:10.120 --> 0:06:13.279 what it really means is that after another five thousand, 0:06:13.279 --> 0:06:16.599 seven hundred years, half of the remaining sample will have decayed, 0:06:16.760 --> 0:06:19.039 leaving you with about a quarter of what you started with. 0:06:19.240 --> 0:06:21.600 And another five thousand, seven hundred years if that means 0:06:21.600 --> 0:06:23.679 you be left with about an eighth of that sample, 0:06:23.760 --> 0:06:28.240 and so on. Carbon fourteen exists naturally on Earth in 0:06:28.360 --> 0:06:31.960 trace amounts. Before the nineteen forties, the carbon fourteen on 0:06:32.040 --> 0:06:36.159 Earth was created through a natural process. Once in a while, 0:06:36.360 --> 0:06:40.120 cosmic rays, these very high energy particles in outer space, 0:06:40.400 --> 0:06:43.880 would collide with an atom in our atmosphere or upper atmosphere, 0:06:44.240 --> 0:06:46.800 and this collision would end up emitting a high energy 0:06:46.839 --> 0:06:50.799 neutron that then could collide with nitrogen atoms that are 0:06:50.839 --> 0:06:54.600 also way up there in our atmosphere. Now, cosmic rays 0:06:54.640 --> 0:06:58.479 are high energy sub atomic particles. They originate outside of 0:06:58.480 --> 0:07:02.839 our solar system, usually are admitted by supernova of massive stars, 0:07:03.200 --> 0:07:06.560 and these sub atomic particles are primarily atomic nuclei and 0:07:06.720 --> 0:07:09.840 high energy protons. So this collision of the high energy 0:07:09.880 --> 0:07:14.120 neutron with the nitrogen forces a proton to leave the 0:07:14.200 --> 0:07:18.400 nucleus and the in fourteen changes to C fourteen. So, 0:07:18.440 --> 0:07:21.080 in other words, nitrogen fourteen turns to carbon fourteen. So 0:07:21.120 --> 0:07:23.720 instead of having seven protons and seven neutrons, the new 0:07:23.760 --> 0:07:27.840 atom has six protons and eight neutrons. The proton that 0:07:27.960 --> 0:07:31.200 was broken off from the nucleus zooms off with an electron, 0:07:31.680 --> 0:07:34.120 so you get one proton and one electron. That means 0:07:34.160 --> 0:07:38.320 you have an atom of hydrogen. So again what's happening 0:07:38.400 --> 0:07:43.560 is a high energy neutron collides with nitrogen fourteen, forces 0:07:43.640 --> 0:07:47.680 out a proton. The proton and an electron high tail 0:07:47.760 --> 0:07:52.480 it and honeymoon off as hydrogen and the incoming neutron 0:07:53.120 --> 0:07:56.280 joins the party, and now you've got carbon fourteen. So 0:07:56.440 --> 0:08:00.320 pre nineteen forties, carbon fourteen is rare because of two reasons. 0:08:00.560 --> 0:08:04.520 It undergoes radioactive decay, so over time it disappears, and 0:08:04.600 --> 0:08:07.120 it's produced by an event that's not super frequent, though 0:08:07.160 --> 0:08:11.360 it's also not uncommon, so it does happen regularly enough 0:08:11.440 --> 0:08:17.640 that carbon fourteen is replenished, but it's a very small 0:08:17.720 --> 0:08:21.520 overall percentage of the carbon here on Earth. We've got 0:08:21.560 --> 0:08:23.920 some more to say about carbon dating in just a second, 0:08:24.000 --> 0:08:34.839 but first let's take a quick break for our sponsor. Now, 0:08:34.920 --> 0:08:38.960 living things here on Earth absorb carbon through various means, 0:08:39.400 --> 0:08:42.400 and some of that carbon is carbon fourteen. So it 0:08:42.559 --> 0:08:45.560 maybe that you know, you eat a plant in that 0:08:45.600 --> 0:08:47.640 plant has some of the carbon fourteen in it. Now 0:08:47.720 --> 0:08:50.160 you have some of the carbon fourteen and you and 0:08:50.200 --> 0:08:53.080 if we know the ratio of carbon fourteen to the 0:08:53.120 --> 0:08:56.800 stable form of carbon twelve, we can look at materials 0:08:56.800 --> 0:08:58.960 and analyze them to see how the ratio of carbon 0:08:59.000 --> 0:09:01.920 fourteen to carbon twelve in the material stacks up to 0:09:02.040 --> 0:09:05.760 the standard ratio. With living things, this becomes a matter 0:09:05.800 --> 0:09:09.200 of looking at how much carbon fourteen is not there? 0:09:10.120 --> 0:09:13.720 All right, That's it's a little confusing. Let me explain. So, 0:09:13.840 --> 0:09:17.640 when a living thing is still alive, it accumulates carbon 0:09:17.679 --> 0:09:21.880 at about the same rate it loses carbon, so carbon 0:09:22.000 --> 0:09:25.760 cosmic rays produced this carbon fourteen frequently enough that the 0:09:25.880 --> 0:09:30.000 ratio between carbon fourteen and carbon twelve remains steady, So 0:09:30.040 --> 0:09:34.679 the percentage of carbon fourteen to carbon twelve is fairly standardized. 0:09:35.080 --> 0:09:38.320 But when a living thing stops being alive and turns 0:09:38.360 --> 0:09:44.080 into a not living anymore thing, it stops accumulating carbon, 0:09:44.440 --> 0:09:47.240 so it has the carbon that it has inside of 0:09:47.280 --> 0:09:51.240 it stays. That's it. You're not losing anymore. You're not 0:09:51.320 --> 0:09:56.360 gaining any more except for carbon fourteen because carbon fourteen 0:09:56.520 --> 0:10:01.080 undergoes radioactive decay, so over time, some of that carbon 0:10:01.200 --> 0:10:06.880 fourteen starts to convert to nitrogen. So that means if 0:10:07.000 --> 0:10:10.560 you can look at the remains of a living thing 0:10:11.160 --> 0:10:15.040 and detect the ratio of carbon fourteen to carbon twelve. 0:10:15.440 --> 0:10:17.760 You can get an idea of how long ago it 0:10:17.960 --> 0:10:21.080 was that it stopped taking in carbon, as in, how 0:10:21.120 --> 0:10:24.240 long ago was it that this lip, once living thing died. 0:10:25.240 --> 0:10:27.160 It gets a little more complicated than all that, but 0:10:27.440 --> 0:10:31.640 here's the basic rule. If we want to be really precise, 0:10:32.040 --> 0:10:35.200 here's the equation we use to determine the age of 0:10:35.240 --> 0:10:39.120 a sample of material. You have an equation where you 0:10:39.160 --> 0:10:43.000 take the natural logarithm of n F divided by n 0:10:43.040 --> 0:10:46.920 o uh that in turn is divided by negative point 0:10:47.000 --> 0:10:49.839 six nine three, and then you multiply it by t 0:10:50.840 --> 0:10:55.920 uh one half, so one half t the natural logarithm 0:10:56.280 --> 0:10:59.800 is a specific logarithm applied to this equation and other 0:10:59.840 --> 0:11:03.240 things as well. N F divided and oh actually refers 0:11:03.280 --> 0:11:06.120 to the percentage of carbon fourteen and the sample compared 0:11:06.120 --> 0:11:10.520 to the amount found in living stuff today at times 0:11:10.559 --> 0:11:13.079 one half is the half life of carbon, so that's 0:11:13.120 --> 0:11:15.760 five thousand, seven hundred years. So it was a lot 0:11:16.080 --> 0:11:18.400 easier to understand this if we take a specific example. 0:11:19.400 --> 0:11:22.480 So let's say you've got a sample of some sort 0:11:22.600 --> 0:11:26.800 of material and you have determined that there is five 0:11:26.840 --> 0:11:29.920 percent of the amount of carbon fourteen in that material 0:11:30.559 --> 0:11:33.400 compared to what you would find in something that is alive. 0:11:33.640 --> 0:11:37.000 Right now, so you take a sample of a living thing, 0:11:37.800 --> 0:11:40.679 and then you take the sample of the thing you're testing. 0:11:41.120 --> 0:11:43.080 You see that the thing you're testing only has five 0:11:43.080 --> 0:11:45.280 percent of the carbon fourteen you would find in living things. 0:11:45.800 --> 0:11:47.440 That means you would fill out the equation with the 0:11:47.559 --> 0:11:53.040 natural logarithm of point zero five divided by negative point 0:11:53.120 --> 0:11:57.160 six nine three, and you multiply that that result to 0:11:57.520 --> 0:12:00.120 with five thousand, seven hundred years. The natural lug ay 0:12:00.120 --> 0:12:01.680 them at point zero five, by the way, in case 0:12:01.720 --> 0:12:04.560 you don't want to whip out your calculator, is negative 0:12:04.600 --> 0:12:08.079 two point nine nine five seven three to two seven 0:12:08.200 --> 0:12:11.720 three five five. If you divide that by negative point 0:12:11.800 --> 0:12:15.400 six nine three, you get four point three to two 0:12:15.679 --> 0:12:21.319 eight four five. Don't dial that number. If you take 0:12:21.400 --> 0:12:24.720 that number, the four point three, etcetera, and you multiply 0:12:24.760 --> 0:12:27.600 that by five thousand, seven hundred years, you end up 0:12:27.640 --> 0:12:30.840 with twenty four thousand, six hundred forty point two years. 0:12:31.120 --> 0:12:34.120 I mean, the stuff you're looking at died somewhere around 0:12:34.160 --> 0:12:37.320 that time frame, give or take thirty two hundred years, 0:12:37.720 --> 0:12:40.160 So somewhere on twenty four thousand, six hundred forty years 0:12:40.160 --> 0:12:44.440 ago is when that thing no longer breathed or lived, 0:12:44.520 --> 0:12:48.120 or however you wanted to find it. By the way, 0:12:48.320 --> 0:12:51.960 this approach does have a limitation. Anything older than sixty 0:12:52.040 --> 0:12:55.080 thousand years is pretty much out of bounds. Carbon fourteen 0:12:55.120 --> 0:12:57.400 just isn't a reliable means of dating that sort of material, 0:12:57.480 --> 0:13:00.120 and we have to rely on other methods so and 0:13:00.200 --> 0:13:04.400 fourteen because of the decay once against two very small amounts, 0:13:04.960 --> 0:13:08.600 it's very difficult to narrow it down to a specific time, 0:13:08.600 --> 0:13:11.040 and if it's long enough, there won't be any carbon 0:13:11.040 --> 0:13:14.079 fourteen at all all the carbon fourteen will have decayed 0:13:14.120 --> 0:13:17.040 by then. You can't use carbon dating if there's no 0:13:17.120 --> 0:13:21.960 carbon fourteen left. So to actually test the carbon fourteen concentration, 0:13:22.679 --> 0:13:26.360 you first have to take the sample, uh whatever object 0:13:26.360 --> 0:13:28.920 it might be. You have to remove part of it, 0:13:29.520 --> 0:13:32.000 and typically you would apply some chemicals to the material, 0:13:32.480 --> 0:13:35.560 usually a very strong acid wash and a strong base wash. 0:13:36.000 --> 0:13:40.600 That's to remove all the contaminating materials that could end 0:13:40.679 --> 0:13:44.480 up giving you false readings on carbon fourteen. Then you 0:13:44.480 --> 0:13:48.600 would burn the sample within a glass container to capture 0:13:48.600 --> 0:13:52.760 the carbon dioxide that is emitted when you burn the material. 0:13:53.320 --> 0:13:56.560 And then you would analyze the carbon dioxide to find 0:13:56.600 --> 0:14:00.000 out the concentration of carbon fourteen. So you can see 0:14:00.000 --> 0:14:02.760 that this approach has a big drawback. It ends up 0:14:02.880 --> 0:14:06.040 damaging whatever it is you are attempting to date in 0:14:06.080 --> 0:14:09.400 the first place. And that's why some particularly high valued 0:14:09.440 --> 0:14:12.760 items go without being tested, because the perception is that 0:14:12.840 --> 0:14:16.679 even a small sample of that original piece would be 0:14:16.679 --> 0:14:21.240 too much damage to to uh make on this item. 0:14:21.360 --> 0:14:25.040 So certain items are considered very precious and there's a 0:14:25.080 --> 0:14:28.920 big resistance to using carbon dating because by definition, you're 0:14:28.920 --> 0:14:32.040 going to be damaging the material. Now, there's several lines 0:14:32.080 --> 0:14:35.960 of research they're exploring possible non destructive means of using 0:14:36.080 --> 0:14:40.800 radiocarbon dating. There's one that uses plasma oxidation and the 0:14:40.920 --> 0:14:44.600 use of non destructive washes to clean samples of those 0:14:44.840 --> 0:14:48.840 contaminating humic acids, which would lead to errors if they 0:14:48.840 --> 0:14:52.920 remain behind. But those are still largely in the testing 0:14:52.960 --> 0:14:56.640 phase and aren't the common means of using carbon dating. Also, 0:14:57.040 --> 0:14:59.600 keep in mind that we use this method to estimate 0:14:59.640 --> 0:15:02.600 the date of things made from organic materials, like the 0:15:02.640 --> 0:15:06.680 Dead Sea scrolls, but this estimation is based upon when 0:15:06.720 --> 0:15:10.000 the materials were harvested So, in other words, whenever the 0:15:10.080 --> 0:15:12.880 living thing that the materials came from stopped being alive, 0:15:14.040 --> 0:15:16.640 it doesn't tell us the date of when the artifact 0:15:16.720 --> 0:15:19.600 was actually produced. So it's possible that you could come 0:15:19.640 --> 0:15:23.480 across an artifact like a scroll, and you use carbon 0:15:23.560 --> 0:15:26.600 dating on it and find out that the scroll material 0:15:27.240 --> 0:15:29.760 is two thousand years old, meaning two thousand years ago 0:15:30.480 --> 0:15:34.480 whatever the scroll was made out of stopped living, But 0:15:34.520 --> 0:15:38.360 it doesn't tell you about the contents written in the scroll. 0:15:38.480 --> 0:15:42.080 It's possible that the contents were added to the scroll 0:15:42.360 --> 0:15:46.920 much after the living thing stopped being alive. Still, it's 0:15:46.920 --> 0:15:49.080 a pretty good bet that the two are within the 0:15:49.120 --> 0:15:52.520 same neighborhood of time, rather than someone held onto blank 0:15:52.600 --> 0:15:55.800 scrolls for a few centuries before finally jotting something down. 0:15:57.280 --> 0:15:59.680 All right, it's all this is cool, But how did 0:15:59.680 --> 0:16:03.000 we even figure out radio Carbon dating would be a 0:16:03.040 --> 0:16:06.920 possible way of figuring out how old something is. Well, 0:16:06.960 --> 0:16:09.360 some early discoveries were made in the nineteen thirties at 0:16:09.360 --> 0:16:13.280 the Lawrence Radiation Laboratory in Berkeley, and you probably remember 0:16:13.320 --> 0:16:15.720 that if you've been listening to tech stuff. It factored 0:16:15.760 --> 0:16:18.120 heavily into the discussion I had with Ben Boland about 0:16:18.160 --> 0:16:24.200 the Manhattan Project. So Franz Curry, an American physicist, observed 0:16:24.240 --> 0:16:27.520 something really interesting when he irradiated a cloud of air 0:16:27.640 --> 0:16:31.760 in a cloud chamber. He used neutrons to UH to 0:16:31.920 --> 0:16:36.400 irradiate that cloud, and he saw proton recoil tracks that 0:16:36.480 --> 0:16:40.920 indicated something was losing protons. So he concluded that the 0:16:41.000 --> 0:16:44.880 neutrons that he was using were colliding with nitrogen fourteen 0:16:45.440 --> 0:16:48.240 and producing what was believed to be a form of 0:16:48.280 --> 0:16:51.720 carbon as a result, with hydrogen being the other product 0:16:51.760 --> 0:16:55.320 of this collision. His work was further explored by physicists 0:16:55.360 --> 0:16:59.640 like Tom W. Bonner, W. M. Brubaker, W. J. Burcham, 0:17:00.000 --> 0:17:04.080 and Maurice gold Hauber. Now collectively, this laid the foundation 0:17:04.119 --> 0:17:07.160 for the simple equation of a high energy neutron plus 0:17:07.280 --> 0:17:12.400 nitrogen fourteen produces one hydrogen atom and one carbon fourteen atom. 0:17:12.520 --> 0:17:15.280 Then you had Narrico Fermi. We talked about him in 0:17:15.320 --> 0:17:18.639 the Manhattan Project, and his work showed that the cross 0:17:18.640 --> 0:17:21.760 section of a nitrogen fourteen atom was much larger than 0:17:21.800 --> 0:17:26.760 other materials, and that suggested that neutron and nitrogen collisions 0:17:26.840 --> 0:17:29.800 might happen fairly regularly in nature as long as there 0:17:29.840 --> 0:17:33.480 were a supply of high energy neutrons. All right, we 0:17:33.600 --> 0:17:36.160 got a little bit more about carbon dating, and then 0:17:36.840 --> 0:17:47.440 what's It's back to reality for me? I guess so 0:17:47.880 --> 0:17:50.320 Sage Korff, who was a physicist who was born in 0:17:50.359 --> 0:17:53.399 Finland and whose family immigrated to the United States in 0:17:53.400 --> 0:17:57.560 the early twentieth century, he discovered the phenomenon that cosmic 0:17:57.680 --> 0:18:01.199 rays interact with atoms and produce high energy neutrons in 0:18:01.240 --> 0:18:06.440 the upper atmosphere. So Pharem's prediction and course observation, we're 0:18:06.480 --> 0:18:11.120 starting to kind of coalesce here. The observations convinced scientists 0:18:11.160 --> 0:18:14.879 that the neutrons themselves were not cosmic rays, because the 0:18:14.880 --> 0:18:18.400 neutrons had a lifespan of just eighteen minutes, and therefore 0:18:19.000 --> 0:18:21.560 a neutron wouldn't be able to survive the long trip 0:18:21.600 --> 0:18:25.120 through space. They must have been something else first, so 0:18:25.160 --> 0:18:27.720 they said the neutrons had to be a byproduct of 0:18:27.760 --> 0:18:31.439 another interaction. A cosmic ray must be interacting with something 0:18:31.440 --> 0:18:35.440 in the atmosphere. That interaction caused this high energy neutron 0:18:35.480 --> 0:18:38.600 to be emitted, and Quarter hypothesized that these neutrons could 0:18:38.640 --> 0:18:41.919 then interact with nitrogen fourteen to produce carbon fourteen in 0:18:41.960 --> 0:18:45.879 the upper atmosphere. Now, it was Willard F. Libby who 0:18:45.960 --> 0:18:48.480 came up with the idea that since carbon fourteen is 0:18:48.560 --> 0:18:51.280 generated at a steady rate due to cosmic ray interactions 0:18:51.280 --> 0:18:54.640 in our atmosphere, you should be able to use it 0:18:54.680 --> 0:18:58.280 to measure how long something has been dead. Libby would 0:18:58.320 --> 0:19:01.520 measure the value of carbon fourteen's half life at five thousand, 0:19:01.640 --> 0:19:04.480 five hundred sixty eight years, give or take thirty years, 0:19:04.840 --> 0:19:08.000 which became known as the Libby half life. And Libby 0:19:08.080 --> 0:19:11.359 himself would be awarded the Nobel Prize in nineteen sixty 0:19:11.440 --> 0:19:15.160 for his work in radiocarbon dating. All right, so that's 0:19:15.200 --> 0:19:18.560 the history of radiocarbon dating and generally how radiocarbon dating works. 0:19:18.920 --> 0:19:22.000 So why is it in trouble or what could possibly 0:19:22.200 --> 0:19:26.120 be causing confusion with radiocarbon dating. Well, there are two 0:19:26.119 --> 0:19:28.840 big things we need to talk about, and one was 0:19:28.960 --> 0:19:30.840 one that I've alluded to a couple of times. I 0:19:30.920 --> 0:19:35.119 mentioned that, you know, pre nineteen forties, you had a 0:19:35.160 --> 0:19:39.520 certain level of carbon fourteen that was pretty standard, but 0:19:39.640 --> 0:19:43.119 the nuclear age really messed things up for us. They 0:19:43.160 --> 0:19:45.879 made carbon fourteen dating a bit tricky. Starting in the 0:19:45.960 --> 0:19:50.000 nineteen forties, we began testing nuclear bombs. Now, these bombs 0:19:50.000 --> 0:19:52.840 released a lot of energy upon exploding, partly in the 0:19:52.880 --> 0:19:55.600 form of high energy neutrons. You could probably see where 0:19:55.600 --> 0:19:58.680 this is going. Some of those high energy neutrons ended 0:19:58.760 --> 0:20:01.719 up interacting with night jan fourteen atoms, which meant that 0:20:01.840 --> 0:20:05.600 it produced carbon fourteen atoms as a result. So the 0:20:05.720 --> 0:20:10.960 concentration of carbon fourteen increased in the wake of nuclear 0:20:11.000 --> 0:20:14.720 bomb testing. So anything that died after the nineteen forties 0:20:14.760 --> 0:20:18.159 actually has a higher concentration of carbon fourteen than the 0:20:18.200 --> 0:20:22.520 stuff that died before the nineteen forties did even at 0:20:22.520 --> 0:20:25.960 the time of death. According to Professor Nalini nod Karnie 0:20:26.080 --> 0:20:29.119 of the Evergreen State College, the nineteen fifties saw a 0:20:29.240 --> 0:20:34.080 one hundred percent spike in carbon fourteen coming into the atmosphere. 0:20:34.800 --> 0:20:38.080 In nineteen sixty three, the United States and Russia agreed 0:20:38.119 --> 0:20:41.359 to stop above ground nuclear testing, and the levels of 0:20:41.359 --> 0:20:44.160 carbon fourteen in the atmosphere gradually dropped down to their 0:20:44.200 --> 0:20:47.119 normal levels. But that means there's a blip in the 0:20:47.160 --> 0:20:51.320 carbon fourteen radar between the nineteen forties and nineteen sixty three. 0:20:51.520 --> 0:20:53.159 So if you put yourself in the shoes of a 0:20:53.280 --> 0:20:58.240 future archaeologist. Radio carbon dating becomes unreliable because the levels 0:20:58.240 --> 0:21:00.920 of carbon fourteen could be decept tip. If the thing 0:21:00.920 --> 0:21:04.520 you're measuring died during the era of nuclear testing, it 0:21:04.600 --> 0:21:07.800 might appear to be younger than you thought because there's 0:21:07.800 --> 0:21:11.480 a higher concentration of carbon fourteen in its sample than 0:21:11.600 --> 0:21:14.840 you otherwise would have expected. So it may seem that 0:21:14.960 --> 0:21:20.000 something died in twenty fifteen as opposed to nineteen sixty three. 0:21:20.680 --> 0:21:24.040 That's just an example. Now to the article that prompted 0:21:24.040 --> 0:21:27.040 this episode in the first place, that's a different case. 0:21:27.400 --> 0:21:30.360 Researchers published a study in the Proceedings of the National 0:21:30.359 --> 0:21:33.320 Academy of Sciences about how the use of fossil fuels 0:21:33.880 --> 0:21:38.000 is further making radiocarbon dating less reliable, and this time 0:21:38.040 --> 0:21:41.040 it's not an excess of carbon fourteen. It's actually the 0:21:41.040 --> 0:21:45.880 opposite problem. Fossil fuels have no carbon fourteen in them 0:21:46.119 --> 0:21:50.800 because they are fossil fuels. This is billions of years old, 0:21:51.440 --> 0:21:54.080 so they're far too old for any carbon fourteen to remain. 0:21:54.160 --> 0:21:57.800 Remember that carbon fourteen is decaying over time and turning 0:21:57.800 --> 0:22:03.200 into nitrogen, so eventually all of those carbon fourteen atoms decay. 0:22:03.320 --> 0:22:06.639 So burning a fossil fuel create releases carbon dioxide, and 0:22:06.680 --> 0:22:09.640 the carbon in that CEO two has no carbon fourteen 0:22:09.640 --> 0:22:13.000 and it's all carbon twolve carbon thirteen. So the more 0:22:13.040 --> 0:22:16.840 fossil fuels we burn, the more we dilute the concentration 0:22:16.840 --> 0:22:20.119 of carbon fourteen that's in the atmosphere. So stuff from 0:22:20.119 --> 0:22:23.080 the nuclear age tends to look younger than it really 0:22:23.160 --> 0:22:26.359 is because of the higher concentration of carbon fourteen. Stuff 0:22:26.440 --> 0:22:29.920 from the later ages of fossil fuel use will look 0:22:30.119 --> 0:22:34.280 older than they really are because carbon fourteen has been diluted. So, 0:22:34.280 --> 0:22:38.000 according to the study, fresh organic material in twenty fifty 0:22:38.280 --> 0:22:41.280 would contain the same amount of carbon fourteen relative to 0:22:41.320 --> 0:22:46.359 carbon twelve as something dating from ten fifty. So you 0:22:46.400 --> 0:22:50.840 have a thousand years of doubt in any radio carbon 0:22:50.920 --> 0:22:54.919 dated samples. You would look at the two samples if 0:22:54.960 --> 0:22:58.400 you if all you had were miniscule samples of two 0:22:58.440 --> 0:23:01.000 things and one of them was a T shirt that 0:23:01.359 --> 0:23:05.400 was made in and another was a piece of cloth 0:23:05.600 --> 0:23:09.280 that dated from ten fifty, and you did radiocarbon dating, 0:23:10.000 --> 0:23:13.280 you'd get the same result. This is not good if 0:23:13.320 --> 0:23:16.280 you are trying to figure out how old something is 0:23:17.520 --> 0:23:20.880 Heather Graven, who authored the study on fossil fuel emissions 0:23:20.920 --> 0:23:23.399 and the effect on radiocarbon dating, says that if we 0:23:23.400 --> 0:23:27.680 were to reduce carbon dioxide emissions drastically in the very 0:23:27.680 --> 0:23:31.359 near future, the effect on future radiocarbon dating would be 0:23:31.359 --> 0:23:34.800 equivalent to inserting a one year error on top of 0:23:34.840 --> 0:23:39.720 any estimation. If we don't drastically reduce emissions, that error 0:23:39.840 --> 0:23:43.320 range will continue to grow over time. One thing that 0:23:43.359 --> 0:23:46.240 the concentration of carbon fourteen tells us is how much 0:23:46.280 --> 0:23:48.760 carbon dioxide in the atmosphere comes from the burning of 0:23:48.800 --> 0:23:52.679 fossil fuels. So as we see the concentration decrease, we 0:23:52.760 --> 0:23:56.439 know that's because proportionally more carbon twelve is being released 0:23:56.440 --> 0:24:00.320 into the atmosphere, diluting the already tiny concentration of carbon fourteen. 0:24:00.600 --> 0:24:03.320 So that's useful for scientists who are studying climate change 0:24:03.320 --> 0:24:07.359 and pollution. That's not exactly a happy story, is it. 0:24:08.520 --> 0:24:13.920 So what are our options if carbon dating becomes unreliable, Well, 0:24:13.960 --> 0:24:16.560 that depends on what you're trying to analyze. If you're 0:24:16.560 --> 0:24:19.680 looking at inorganic stuff like rocks, you don't need to 0:24:19.760 --> 0:24:22.040 use carbon fourteen in the first place. That would be 0:24:22.160 --> 0:24:25.160 pretty much useless. You would use something else like potassium 0:24:25.320 --> 0:24:28.159 argon dating, which is useful to estimate the age of 0:24:28.280 --> 0:24:30.840 rocks that are a hundred thousand years old or younger. 0:24:31.400 --> 0:24:32.959 And if that's not a big enough range, you can 0:24:33.000 --> 0:24:36.320 actually use uranium lead dating, and that will let you 0:24:36.440 --> 0:24:40.560 estimate rocks between one point four and five million years old. 0:24:41.240 --> 0:24:43.240 There's a lot of different options if you're trying to 0:24:43.320 --> 0:24:45.880 date stuff. When it comes to organic materials, however, it's 0:24:45.880 --> 0:24:49.000 a lot more tricky. Radio carbon was a great tool, 0:24:49.960 --> 0:24:53.280