WEBVTT - TechStuff Classic: Is Carbon Dating on the way out? 0:00:04.400 --> 0:00:07.800 Welcome to tech Stuff, a production from I Heart Radio. 0:00:11.840 --> 0:00:14.800 Hey there, and welcome to tech Stuff. I'm your host 0:00:14.880 --> 0:00:17.720 Jonathan Strickland. I'm an executive producer with I Heart Radio, 0:00:17.800 --> 0:00:20.759 and how the tech are you? It is time for 0:00:20.880 --> 0:00:25.959 a tech Stuff classic episode. This episode originally aired on 0:00:26.120 --> 0:00:30.840 August tenth, two thousand fifteen. It is titled is carbon 0:00:30.960 --> 0:00:34.120 Dating on the Way out? This episode might need to 0:00:34.159 --> 0:00:38.320 be carbon dated. Let's take a listen. This comes from 0:00:38.440 --> 0:00:42.440 nikkil Cardale, and I do apologize that I'm sure I 0:00:42.640 --> 0:00:46.440 mispronounced your name, but uh, the request was could you 0:00:46.520 --> 0:00:50.280 do an episode explaining this carbon dating is pretty useful? 0:00:50.320 --> 0:00:56.080 So this effect seems relevant and uh. Cardale actually uh 0:00:56.560 --> 0:01:00.000 commented on and and included another tweet from real scientists 0:01:00.800 --> 0:01:04.600 that including an article titled will our fossil use ruin 0:01:04.760 --> 0:01:07.800 our ability to use carbon dating as a scientific tool? 0:01:08.760 --> 0:01:12.759 This is really fascinating the idea of using carbon dating, uh, 0:01:12.840 --> 0:01:17.839 and how that that method might be in jeopardy because 0:01:18.200 --> 0:01:21.120 of the use of fossil fuels. So I thought I 0:01:21.160 --> 0:01:24.679 would go into that explain what carbon dating is and 0:01:24.840 --> 0:01:28.240 why it might not be an accurate means of telling 0:01:28.280 --> 0:01:32.680 how old something is after too long So going into 0:01:32.760 --> 0:01:35.440 the article, it's about how the enormous amount of carbon 0:01:35.440 --> 0:01:38.720 emissions we generate could make carbon dating and unreliable means 0:01:38.760 --> 0:01:42.120 to determine the age of certain types of materials. But 0:01:42.240 --> 0:01:45.199 to understand how that's possible, we need to know how 0:01:45.319 --> 0:01:49.760 carbon dating works first, So we're gonna do a carbon 0:01:49.880 --> 0:01:52.760 dating one oh one. Now, the first thing that we 0:01:52.800 --> 0:01:57.240 have to talk about is carbon fourteen. So the fourteen 0:01:57.520 --> 0:02:00.760 in carbon fourteen tells us it's an isotope of carbon. 0:02:01.480 --> 0:02:05.520 This particular isotope must have eight neutrons because carbon has 0:02:05.560 --> 0:02:09.040 six protons. You can change the number of neutrons in 0:02:09.080 --> 0:02:12.960 an atom, that's the different types of isotopes atoms may have, 0:02:13.320 --> 0:02:16.080 but you can't change the number of protons and atom 0:02:16.120 --> 0:02:19.600 has without changing that element. So carbon has six protons, 0:02:19.840 --> 0:02:21.840 and if you change that number of protons, you change 0:02:21.880 --> 0:02:26.440 the element itself. It acts reacts differently in chemical operations, 0:02:27.040 --> 0:02:31.840 and uh is no longer carbon. So carbon twelve is 0:02:31.919 --> 0:02:35.600 the most common form of carbon that we find. It 0:02:35.639 --> 0:02:38.920 has six protons and six neutrons. Then you have carbon thirteen, 0:02:38.960 --> 0:02:41.600 which is six protons and seven neutrons, and both of 0:02:41.600 --> 0:02:45.800 those are stable forms of carbon that means they don't decay. 0:02:45.960 --> 0:02:49.080 So if you have carbon twelve or carbon thirteen, you 0:02:49.080 --> 0:02:51.600 put it in a box and you leave for I 0:02:51.639 --> 0:02:54.600 don't know, two billion years, and you come back, you're 0:02:54.639 --> 0:02:57.680 still gonna have carbon twelve or carbon thirteen because they 0:02:57.720 --> 0:03:01.640 remain stable they do not decay. But carbon fourteen is different. 0:03:01.919 --> 0:03:07.280 It is a radio isotope. Radioisotopes are also known as 0:03:07.480 --> 0:03:12.040 radio nucleides, and these are isotopes of a particular atom 0:03:12.200 --> 0:03:16.320 that have an unstable nucleus. These isotopes undergo what we 0:03:16.360 --> 0:03:19.840 call nuclear decay, and in that process they release some 0:03:19.960 --> 0:03:23.720 excess energy in the form of stuff like gamma rays 0:03:23.720 --> 0:03:28.360 and or subatomic particles. Carbon fourteen undergoes what is called 0:03:28.760 --> 0:03:32.840 beta decay. So when it decays, one of the neutrons 0:03:32.880 --> 0:03:37.320 in the nucleus spontaneously changes into a proton, an electron, 0:03:37.680 --> 0:03:41.560 and an anti neutrino. The nucleus gives the boot to 0:03:41.560 --> 0:03:45.440 the electron and the anti neutrino, but the proton stays behind, 0:03:45.520 --> 0:03:48.880 which means the atom no longer is a carbon atom. 0:03:48.920 --> 0:03:52.080 Since again we mentioned that atoms depend upon the number 0:03:52.120 --> 0:03:55.920 of protons and the nucleus, so the carbon fourteen decays 0:03:56.000 --> 0:04:01.720 into nitrogen fourteen, and nitrogen fourteen has seven protons and 0:04:01.840 --> 0:04:04.840 seven neutrons. Also, by the way, one of the few 0:04:05.080 --> 0:04:08.920 stable elements that has both an odd number of protons 0:04:09.000 --> 0:04:13.240 and an odd number of neutrons uh, and nitrogen fourteen 0:04:13.440 --> 0:04:16.640 is stable. It makes up the vast majority of the 0:04:16.720 --> 0:04:21.360 nitrogen found naturally unearthed, More than of the nitrogen found 0:04:21.360 --> 0:04:25.920 on Earth is nitrogen fourteen. So radioactive decay occurs naturally 0:04:26.080 --> 0:04:29.719 within these isotopes, and it's a spontaneous occurrence. That's really 0:04:29.800 --> 0:04:33.520 important to remember. Carbon fourteen has a radioactive half life 0:04:33.560 --> 0:04:38.400 of about five thousand, seven hundred years. There's some confusion 0:04:38.440 --> 0:04:40.880 about what that means. I find in day to day 0:04:40.880 --> 0:04:43.520 conversations with people who haven't had science in a while. 0:04:43.760 --> 0:04:46.800 You guys who have recently had this in science class, 0:04:46.800 --> 0:04:49.520 you're rolling your eyes right now. But for adults who 0:04:49.520 --> 0:04:52.040 have not taken a science class in a long time, 0:04:52.360 --> 0:04:56.800 this might require some some refreshing. So half life of 0:04:56.880 --> 0:05:00.200 five thousand, seven hundred years, what does that mean? It 0:05:00.240 --> 0:05:03.160 means if you have a given amount of carbon fourteen, 0:05:03.760 --> 0:05:07.560 after five thousand, seven hundred years or so, you'll have 0:05:07.920 --> 0:05:11.240 only half of that carbon fourteen remaining. The other half 0:05:11.400 --> 0:05:16.440 having undergone decay radioactive decay and turning into nitrogen. Now, 0:05:16.480 --> 0:05:18.919 this doesn't mean that all the carbon fourteen will be 0:05:18.920 --> 0:05:22.320 gone after another five thousand, seven hundred years, nor does 0:05:22.360 --> 0:05:25.320 it mean that carbon fourteen has a full life of 0:05:25.360 --> 0:05:28.479 eleven thousand, four hundred years or anything like that. In fact, 0:05:28.560 --> 0:05:31.640 what it really means is that after another five thousand, 0:05:31.720 --> 0:05:35.039 seven hundred years, half of the remaining sample will have decayed, 0:05:35.160 --> 0:05:37.479 leaving you with about a quarter of what you started with. 0:05:37.680 --> 0:05:40.000 And another five thousand, seven hundred years if that means 0:05:40.000 --> 0:05:42.120 you'd be left with about an eighth of that sample, 0:05:42.200 --> 0:05:46.680 and so on. Carbon fourteen exists naturally on Earth in 0:05:46.760 --> 0:05:50.400 trace amounts. Before the nineteen forties, the carbon fourteen on 0:05:50.480 --> 0:05:54.599 Earth was created through a natural process. Once in a while, 0:05:54.800 --> 0:05:58.560 cosmic rays, these very high energy particles in outer space, 0:05:58.800 --> 0:06:02.320 would collide with an atom in our atmosphere or upper atmosphere, 0:06:02.680 --> 0:06:05.240 and this collision would end up emitting a high energy 0:06:05.279 --> 0:06:09.200 neutron that then could collide with nitrogen atoms that are 0:06:09.240 --> 0:06:13.000 also way up there in our atmosphere. Now, cosmic rays 0:06:13.040 --> 0:06:16.919 are high energy sub atomic particles. They originate outside of 0:06:16.920 --> 0:06:21.320 our solar system, usually they're emitted by supernova of massive stars, 0:06:21.640 --> 0:06:25.360 and these subatomic particles are primarily atomic nuclei and high 0:06:25.520 --> 0:06:28.760 energy protons. So this collision of the high energy neutron 0:06:28.880 --> 0:06:33.640 with the nitrogen forces a proton to leave the nucleus 0:06:33.680 --> 0:06:36.960 and the IN fourteen changes to C fourteen, So in 0:06:36.960 --> 0:06:39.839 other words, nitrogen fourteen turns to carbon fourteen. So instead 0:06:39.839 --> 0:06:42.479 of having seven protons and seven neutrons, the new atom 0:06:42.520 --> 0:06:46.479 has six protons and eight neutrons. The proton that was 0:06:46.560 --> 0:06:49.640 broken off from the nucleus zooms off with an electron, 0:06:50.120 --> 0:06:52.560 so you get one proton and one electron. That means 0:06:52.600 --> 0:06:56.760 you have an atom of hydrogen. So again what's happening 0:06:56.839 --> 0:07:02.000 is a high energy neutron collides with hydrogen fourteen, forces 0:07:02.080 --> 0:07:06.080 out a proton. The proton and an electron high tail 0:07:06.160 --> 0:07:10.920 it and honeymoon off as hydrogen, and the incoming neutron 0:07:11.560 --> 0:07:14.760 joins the party, and now you've got carbon fourteen. So 0:07:14.880 --> 0:07:18.760 pre nineties, carbon fourteen is rare because of two reasons. 0:07:19.000 --> 0:07:22.960 It undergoes radioactive decay, so over time it disappears, and 0:07:23.040 --> 0:07:25.560 it's produced by an event that's not super frequent, though 0:07:25.600 --> 0:07:29.800 it's also not uncommon, so it does happen regularly enough 0:07:29.880 --> 0:07:36.040 that carbon fourteen is replenished, but it's a very small 0:07:36.160 --> 0:07:40.280 overall percentage of the carbon here on Earth. We'll be 0:07:40.280 --> 0:07:42.880 back with more of this classic episode of tech stuff 0:07:42.920 --> 0:07:54.679 after this quick break. Now, living things here on Earth 0:07:55.160 --> 0:07:59.000 absorb carbon through various means, and some of that carbon 0:07:59.160 --> 0:08:02.920 is carbon fort So it maybe that you know, you 0:08:03.160 --> 0:08:05.120 eat a plant and that plant has some of the 0:08:05.120 --> 0:08:06.920 carbon fourteen in it. Now you have some of the 0:08:06.920 --> 0:08:10.000 carbon fourteen and you And if we know the ratio 0:08:10.120 --> 0:08:13.640 of carbon fourteen to the stable form of carbon twelve, 0:08:14.280 --> 0:08:16.480 we can look at materials and analyze them to see 0:08:16.520 --> 0:08:19.160 how the ratio of carbon fourteen to carbon twelve in 0:08:19.200 --> 0:08:23.559 the material stacks up to the standard ratio. With living things, 0:08:23.600 --> 0:08:25.640 this becomes a matter of looking at how much carbon 0:08:25.680 --> 0:08:30.880 fourteen is not there? All right, That's it's a little confusing. 0:08:31.000 --> 0:08:34.480 Let me explain. So, when a living thing is still alive, 0:08:35.000 --> 0:08:38.280 it accumulates carbon at about the same rate it loses carbon. 0:08:39.200 --> 0:08:43.920 So carbon cosmic rays produced this carbon fourteen frequently enough 0:08:44.000 --> 0:08:48.439 that the ratio between carbon fourteen and carbon twelve remains steady. 0:08:48.480 --> 0:08:51.640 So the percentage of carbon fourteen to carbon twelve is 0:08:51.880 --> 0:08:56.280 fairly standardized. But when a living thing stops being alive 0:08:56.480 --> 0:09:00.600 and turns into a not living any more or thing, 0:09:01.160 --> 0:09:04.960 it stops accumulating carbon, so it has the carbon that 0:09:05.000 --> 0:09:08.800 it has inside of it stays. That's it. You're not 0:09:08.840 --> 0:09:12.760 losing anymore. You're not gaining any more except for carbon 0:09:12.840 --> 0:09:18.360 fourteen because carbon fourteen undergoes radioactive decay, so over time, 0:09:18.840 --> 0:09:22.480 some of that carbon fourteen starts to convert to nitrogen. 0:09:23.520 --> 0:09:28.200 So that means if you can look at the remains 0:09:28.360 --> 0:09:31.920 of a living thing and detect the ratio of carbon 0:09:31.960 --> 0:09:35.520 fourteen to carbon twelve, you can get an idea of 0:09:35.520 --> 0:09:38.680 how long ago it was that it stopped taking in carbon, 0:09:38.880 --> 0:09:41.280 as in, how long ago was it that this lip 0:09:41.440 --> 0:09:45.199 once living thing died. It gets a little more complicated 0:09:45.240 --> 0:09:48.840 than all that, but here's the basic rule. If we 0:09:48.880 --> 0:09:52.000 want to be really precise, here's the equation we use 0:09:52.240 --> 0:09:56.160 to determine the age of a sample of material. You 0:09:56.600 --> 0:10:00.120 have an equation where you take the natural logarithm of 0:10:00.480 --> 0:10:03.880 NF divided by n o uh that in turn is 0:10:03.880 --> 0:10:07.280 divided by negative point six nine three, and then you 0:10:07.360 --> 0:10:12.000 multiply it by t uh one half, so one half t. 0:10:12.800 --> 0:10:17.120 The natural logarithm is a specific logarithm applied to this 0:10:17.160 --> 0:10:20.480 equation and other things as well. NF divided way n 0:10:20.520 --> 0:10:23.880 O actually refers to the percentage of carbon fourteen and 0:10:23.920 --> 0:10:27.319 the sample compared to the amount found in living stuff today, 0:10:28.160 --> 0:10:31.200 and T times one half is the half life of carbon. 0:10:31.360 --> 0:10:34.160 So that's five thousand, seven hundred years. So it's a 0:10:34.200 --> 0:10:37.040 lot easier to understand this if we take a specific example. 0:10:38.000 --> 0:10:41.120 So let's say you've got a sample of some sort 0:10:41.200 --> 0:10:45.400 of material and you have determined that there is five 0:10:45.480 --> 0:10:48.560 percent of the amount of carbon fourteen in that material 0:10:49.160 --> 0:10:51.559 compared to what you would find in something that is 0:10:51.600 --> 0:10:55.000 alive right now, So you take a sample of a 0:10:55.040 --> 0:10:58.439 living thing, and then you take the sample of the 0:10:58.480 --> 0:11:01.280 thing you're testing. You either the thing you're testing only 0:11:01.320 --> 0:11:03.240 has five percent of the carbon fourteen you would find 0:11:03.240 --> 0:11:05.360 in living things. That means you would fill out the 0:11:05.360 --> 0:11:10.000 equation with the natural logarithm of point zero five divided 0:11:10.040 --> 0:11:14.280 by negative point six nine three, and you multiply that 0:11:14.280 --> 0:11:18.000 that result to with five thousand, seven hundred years the 0:11:18.080 --> 0:11:20.080 natural logorithm at point zero five. By the way, in 0:11:20.120 --> 0:11:22.560 case you don't want to whip out your calculator is 0:11:22.679 --> 0:11:26.319 negative two point nine nine five seven three to two 0:11:26.440 --> 0:11:29.720 seven three five five. If you divide that by negative 0:11:30.080 --> 0:11:33.480 point six nine three, you get four point three to 0:11:33.640 --> 0:11:39.640 two eight four five nine. Don't dial that number. If 0:11:39.679 --> 0:11:42.720 you take that number, the four point three, etcetera, and 0:11:42.720 --> 0:11:45.800 you multiply that by five thousand, seven hundred years, you 0:11:45.920 --> 0:11:48.800 end up with twenty four thousand, six hundred forty point 0:11:48.880 --> 0:11:52.079 two years, meaning the stuff you're looking at died somewhere 0:11:52.320 --> 0:11:55.960 around that time frame, give or take thirty two hundred years. 0:11:56.360 --> 0:11:58.760 So somewhere on twenty four thousand, six hundred forty years 0:11:58.800 --> 0:12:03.080 ago is when that thing no longer breathed or lived, 0:12:03.160 --> 0:12:06.760 or however you wanted to define it. By the way, 0:12:06.920 --> 0:12:10.600 this approach does have a limitation. Anything older than sixty 0:12:10.640 --> 0:12:13.720 thou years is pretty much out of bounds. Carbon fourteen 0:12:13.760 --> 0:12:16.040 just isn't a reliable means of dating that sort of material, 0:12:16.080 --> 0:12:19.240 and we have to rely on other methods. So carbon fourteen, 0:12:19.679 --> 0:12:22.959 because of the decay once against two very small amounts, 0:12:23.559 --> 0:12:27.200 it's very difficult to narrow it down to a specific time, 0:12:27.240 --> 0:12:29.640 and if it's long enough, there won't be any carbon 0:12:29.679 --> 0:12:32.720 fourteen at all. All the carbon fourteen will have decayed 0:12:32.720 --> 0:12:35.679 by then you can't use carbon dating if there's no 0:12:35.760 --> 0:12:40.560 carbon fourteen left. So to actually test the carbon fourteen concentration, 0:12:41.280 --> 0:12:44.920 you first have to take the sample, uh whatever object 0:12:45.000 --> 0:12:47.520 it might be. You have to remove part of it, 0:12:48.120 --> 0:12:50.640 and typically you would apply some chemicals to the material, 0:12:51.120 --> 0:12:54.160 usually a very strong acid wash and a strong base wash. 0:12:54.600 --> 0:12:59.240 That's to remove all the contaminating materials that could end 0:12:59.320 --> 0:13:03.079 up giving you false readings on carbon fourteen. Then you 0:13:03.120 --> 0:13:07.199 would burn the sample within a glass container to capture 0:13:07.240 --> 0:13:11.400 the carbon dioxide that is emitted when you burn the material, 0:13:11.920 --> 0:13:15.160 and then you would analyze the carbon dioxide to find 0:13:15.200 --> 0:13:18.600 out the concentration of carbon fourteen. So you can see 0:13:18.600 --> 0:13:21.400 that this approach has a big drawback. It ends up 0:13:21.480 --> 0:13:24.640 damaging whatever it is you are attempting to date in 0:13:24.679 --> 0:13:28.040 the first place. And that's why some particularly high valued 0:13:28.040 --> 0:13:31.360 items go without being tested, because the perception is that 0:13:31.440 --> 0:13:35.280 even a small sample of that original piece would be 0:13:35.320 --> 0:13:39.920 too much damage to to uh make on this item. 0:13:39.960 --> 0:13:43.680 So certain items are considered very precious and there's a 0:13:43.679 --> 0:13:47.360 big resistance to using carbon dating because by the definition, 0:13:47.360 --> 0:13:50.439 you're going to be damaging the material. Now there's several 0:13:50.440 --> 0:13:54.079 lines of research that are exploring possible non destructive means 0:13:54.160 --> 0:13:58.920 of using radiocarbon dating. There's one that uses plasma oxidation 0:13:59.200 --> 0:14:02.640 and the use of non destructive washes to clean samples 0:14:02.760 --> 0:14:07.160 of those contaminating humic acids, which would lead to errors 0:14:07.200 --> 0:14:10.960 if they remained behind, but those are still largely in 0:14:10.960 --> 0:14:14.200 the testing phase and aren't the common means of using 0:14:14.200 --> 0:14:17.040 carbon dating. Also, keep in mind that we use this 0:14:17.160 --> 0:14:20.920 method to estimate the date of things made from organic materials, 0:14:20.960 --> 0:14:24.760 like the Dead Sea scrolls, but this estimation is based 0:14:24.800 --> 0:14:27.880 upon when the materials were harvested, so, in other words, 0:14:28.160 --> 0:14:30.920 whenever the living thing that the materials came from stopped 0:14:30.920 --> 0:14:34.640 being alive, it doesn't tell us the date of when 0:14:34.640 --> 0:14:37.880 the artifact was actually produced. So it's possible that you 0:14:37.880 --> 0:14:41.440 could come across an artifact like a scroll and you 0:14:41.560 --> 0:14:44.160 use carbon dating on it and find out that the 0:14:44.320 --> 0:14:47.800 scroll material is two thousand years old, meaning two thousand 0:14:47.920 --> 0:14:52.360 years ago whatever the scroll was made out of stopped living, 0:14:53.040 --> 0:14:56.320 but it doesn't tell you about the contents written in 0:14:56.360 --> 0:15:00.200 the scroll. It's possible that the contents were at to 0:15:00.240 --> 0:15:04.280 the scroll much after the living thing stopped being alive. 0:15:04.400 --> 0:15:07.320 Still it's a pretty good bet that the two are 0:15:07.320 --> 0:15:10.360 within the same neighborhood of time, rather than someone held 0:15:10.400 --> 0:15:13.720 onto blank scrolls for a few centuries before finally jotting 0:15:13.760 --> 0:15:17.200 something down. All Right, it's all this is cool, But 0:15:17.920 --> 0:15:21.360 how did we even figure out radio carbon dating would 0:15:21.400 --> 0:15:25.560 be a possible way of figuring out how old something is. Well. 0:15:25.560 --> 0:15:27.960 Some early discoveries were made in the nineteen thirties at 0:15:27.960 --> 0:15:31.920 the Lawrence Radiation Laboratory in Berkeley, and you probably remember 0:15:31.920 --> 0:15:34.360 that if you've been listening to tech stuff. It factored 0:15:34.360 --> 0:15:36.760 heavily into the discussion I had with Ben Bolan about 0:15:36.760 --> 0:15:42.840 the Manhattan Project. So Franz Curry, an American physicist, observed 0:15:42.880 --> 0:15:46.080 something really interesting when he irradiated a cloud of air 0:15:46.280 --> 0:15:50.360 in a cloud chamber. He used neutrons to uh to 0:15:50.520 --> 0:15:55.040 irradiate that cloud, and he saw proton recoil tracks that 0:15:55.080 --> 0:15:59.520 indicated something was losing protons. So he concluded that the 0:15:59.600 --> 0:16:02.960 neutral rons that he was using, we're colliding with nitrogen 0:16:03.040 --> 0:16:06.680 fourteen and producing what was believed to be a form 0:16:06.720 --> 0:16:09.880 of carbon as a result, with hydrogen being the other 0:16:09.920 --> 0:16:13.200 product of this collision. His work was further explored by 0:16:13.240 --> 0:16:18.280 physicists like Tom W. Bonner, W. M. Brubaker, W. J. Bircham, 0:16:18.560 --> 0:16:22.680 and Maurice gold Hauber. Now collectively, this laid the foundation 0:16:22.760 --> 0:16:25.760 for the simple equation of a high energy neutron plus 0:16:25.920 --> 0:16:31.040 nitrogen fourteen produces one hydrogen atom and one carbon fourteen atom. 0:16:31.120 --> 0:16:33.920 Then you had Enrico Fermi. We talked about him in 0:16:33.960 --> 0:16:37.240 the Manhattan Project, and his work showed that the cross 0:16:37.280 --> 0:16:40.400 section of a nitrogen fourteen atom was much larger than 0:16:40.400 --> 0:16:45.400 other materials, and that suggested that neutron and nitrogen collisions 0:16:45.440 --> 0:16:48.440 might happen fairly regularly in nature as long as there 0:16:48.480 --> 0:16:52.760 were a supply of high energy neutrons. Stay tuned for 0:16:52.800 --> 0:16:56.760 the exciting conclusion of this textuff classic episode right after 0:16:56.800 --> 0:17:08.600 we take this break. Then you have a Serge Korf, 0:17:09.000 --> 0:17:11.439 who was a physicist who was born in Finland and 0:17:11.440 --> 0:17:13.960 whose family immigrated to the United States in the early 0:17:14.000 --> 0:17:18.880 twentieth century. He discovered the phenomenon that cosmic rays interact 0:17:18.920 --> 0:17:22.399 with atoms and produce high energy neutrons in the upper atmosphere. 0:17:22.680 --> 0:17:28.040 So Pharem's prediction and corpse observation we're starting to kind 0:17:28.080 --> 0:17:31.960 of coalesce here. The observations convinced scientists that the neutrons 0:17:32.000 --> 0:17:35.679 themselves were not cosmic rays, because the neutrons had a 0:17:35.680 --> 0:17:40.080 lifespan of just eighteen minutes, and therefore a neutron wouldn't 0:17:40.080 --> 0:17:42.560 be able to survive the long trip through space. They 0:17:42.640 --> 0:17:45.720 must have been something else first, so they said the 0:17:45.720 --> 0:17:49.280 neutrons had to be a byproduct of another interaction. A 0:17:49.320 --> 0:17:52.480 cosmic ray must be interacting with something in the atmosphere. 0:17:52.880 --> 0:17:56.280 That interaction caused this high energy neutron to be emitted, 0:17:56.560 --> 0:17:59.480 and Core hypothesized that these neutrons could then interact with 0:17:59.600 --> 0:18:04.440 nitrogen and fourteen to produce carbon fourteen in the upper atmosphere. Now, 0:18:04.440 --> 0:18:06.639 it was Willard F. Libby who came up with the 0:18:06.720 --> 0:18:09.760 idea that since carbon fourteen is generated at a steady 0:18:09.880 --> 0:18:12.719 rate due to cosmic ray interactions in our atmosphere, you 0:18:12.760 --> 0:18:16.000 should be able to use it to measure how long 0:18:16.160 --> 0:18:19.200 something has been dead. Libby would measure the value of 0:18:19.240 --> 0:18:22.800 carbon fourteen's half life at five thousand, five hundred sixty 0:18:22.800 --> 0:18:25.840 eight years, give or take thirty years, which became known 0:18:25.920 --> 0:18:29.000 as the Libby half life, and Libby himself would be 0:18:29.000 --> 0:18:32.120 awarded the Nobel Prize in nineteen sixty for his work 0:18:32.160 --> 0:18:35.800 in radiocarbon dating. All right, So that's the history of 0:18:35.880 --> 0:18:39.920 radiocarbon dating and generally how radiocarbon dating works. So why 0:18:40.040 --> 0:18:43.280 is it in trouble or what could possibly be causing 0:18:43.320 --> 0:18:46.800 confusion with radiocarbon dating. Well, there are two big things 0:18:46.800 --> 0:18:49.439 we need to talk about, and one was one that 0:18:49.480 --> 0:18:51.720 I've alluded to a couple of times. I mentioned that, 0:18:52.720 --> 0:18:56.119 you know, pre nineteen forties, you had a certain level 0:18:56.240 --> 0:19:00.440 of carbon fourteen that was pretty standard, but the nuclear 0:19:00.480 --> 0:19:04.119 age really messed things up for us. They made carbon 0:19:04.160 --> 0:19:06.880 fourteen dating a bit tricky. Starting in the nineteen forties, 0:19:06.920 --> 0:19:10.600 we began testing nuclear bombs. Now, these bombs released a 0:19:10.600 --> 0:19:13.520 lot of energy upon exploding, partly in the form of 0:19:13.600 --> 0:19:16.280 high energy neutrons. You can probably see where this is going. 0:19:16.680 --> 0:19:19.760 Some of those high energy neutrons ended up interacting with 0:19:19.920 --> 0:19:23.520 nitrogen fourteen atoms, which meant that it produced carbon fourteen 0:19:23.560 --> 0:19:27.840 atoms as a result. So the concentration of carbon fourteen 0:19:28.280 --> 0:19:33.040 increased in the wake of nuclear bomb testing. So anything 0:19:33.080 --> 0:19:36.080 that died after the nineteen forties actually has a higher 0:19:36.119 --> 0:19:39.800 concentration of carbon fourteen than the stuff that died before 0:19:39.920 --> 0:19:43.440 the nineteen forties did even know at the time of death. 0:19:43.640 --> 0:19:47.840 According to Professor Nalini no Khannie of the Evergreen State College, 0:19:48.040 --> 0:19:51.919 the nineteen fifties saw a one hundred percent spike in 0:19:52.040 --> 0:19:56.160 carbon fourteen coming into the atmosphere. In nineteen sixty three, 0:19:56.560 --> 0:19:59.600 the United States and Russia agreed to stop above ground 0:19:59.720 --> 0:20:02.280 nucle you're testing, and the levels of carbon fourteen in 0:20:02.280 --> 0:20:05.560 the atmosphere gradually dropped down to their normal levels. But 0:20:05.640 --> 0:20:08.679 that means there's a blip in the carbon fourteen radar 0:20:08.760 --> 0:20:11.919 between the nineteen forties and nineteen sixty three. So if 0:20:11.920 --> 0:20:14.720 you put yourself in the shoes of a future archaeologist, 0:20:15.240 --> 0:20:19.320 radiocarbon dating becomes unreliable because the levels of carbon fourteen 0:20:19.400 --> 0:20:22.679 could be deceptive. If the thing you're measuring died during 0:20:22.720 --> 0:20:25.600 the era of nuclear testing, it might appear to be 0:20:25.760 --> 0:20:29.040 younger than you thought because there's a higher concentration of 0:20:29.119 --> 0:20:33.520 carbon fourteen in its sample than you otherwise would have expected. 0:20:33.840 --> 0:20:38.160 So it may seem that something died in twenty fifteen 0:20:38.200 --> 0:20:41.879 as opposed to nineteen sixty three. That's just an example. 0:20:42.440 --> 0:20:44.840 Now to the article that prompted this episode in the 0:20:44.880 --> 0:20:49.040 first place, that's a different case. Researchers published a study 0:20:49.040 --> 0:20:51.960 in the Proceedings of the National Academy of Sciences about 0:20:52.000 --> 0:20:55.639 how the use of fossil fuels is further making radiocarbon 0:20:55.720 --> 0:20:59.560 dating less reliable, and this time it's not an excess 0:20:59.600 --> 0:21:03.000 of carbon and fourteen. It's actually the opposite problem. Fossil 0:21:03.040 --> 0:21:07.120 fuels have no carbon fourteen in them because they are 0:21:07.200 --> 0:21:12.000 fossil fuels. This is billions of years old, so they're 0:21:12.000 --> 0:21:14.679 far too old for any carbon fourteen to remain. Remember 0:21:14.680 --> 0:21:18.720 that carbon fourteen is decaying over time and turning into nitrogen, 0:21:18.840 --> 0:21:23.600 so eventually all of those carbon fourteen atoms decay. So 0:21:23.640 --> 0:21:27.360 burning a fossil fuel releases carbon dioxide, and the carbon 0:21:27.520 --> 0:21:30.120 in that CEO two has no carbon fourteen and it's 0:21:30.160 --> 0:21:33.840 all carbon toolver carbon thirteen. So the more fossil fuels 0:21:33.880 --> 0:21:37.480 we burn, the more we dilute the concentration of carbon 0:21:37.520 --> 0:21:40.800 fourteen that's in the atmosphere. So stuff from the nuclear 0:21:40.840 --> 0:21:44.040 age tends to look younger than it really is because 0:21:44.040 --> 0:21:47.080 of the higher concentration of carbon fourteen. Stuff from the 0:21:47.160 --> 0:21:51.000 later ages of fossil fuel use will look older than 0:21:51.040 --> 0:21:54.439 they really are because carbon fourteen has been diluted So 0:21:54.480 --> 0:21:58.159 according to the study, fresh organic material in twenty fifty 0:21:58.440 --> 0:22:01.280 would contain the same amount of AREB and fourteen relative 0:22:01.359 --> 0:22:06.359 to carbon twelve as something dating from ten fifty. So 0:22:06.480 --> 0:22:11.000 you have a thousand years of doubt in any radiocarbon 0:22:11.119 --> 0:22:14.960 dated samples. You would be look at the two samples 0:22:14.960 --> 0:22:18.280 if you if all you had were miniscule samples of 0:22:18.359 --> 0:22:20.520 two things and one of them was a T shirt 0:22:21.080 --> 0:22:24.119 that was made in twenty fifty, and another was a 0:22:24.160 --> 0:22:28.080 piece of cloth that dated from ten fifty, and you 0:22:28.119 --> 0:22:32.560 did radiocarbon dating, you'd get the same result. This is 0:22:32.560 --> 0:22:35.160 not good if you are trying to figure out how 0:22:35.240 --> 0:22:39.840 old something is. Heather Graven, who authored the study on 0:22:39.880 --> 0:22:43.080 fossil fuel emissions and the effect on radiocarbon dating, says 0:22:43.119 --> 0:22:47.280 that if we were to reduce carbon dioxide emissions drastically 0:22:47.359 --> 0:22:50.919 in the very near future, the effect on future radiocarbon 0:22:51.000 --> 0:22:54.359 dating would be equivalent to inserting a one year error 0:22:54.440 --> 0:22:59.440 on top of any estimation. If we don't drastically reduce emissions, 0:22:59.480 --> 0:23:03.160 that error age will continue to grow over time. One 0:23:03.200 --> 0:23:06.000 thing that the concentration of carbon fourteen tells us is 0:23:06.000 --> 0:23:08.520 how much carbon dioxide in the atmosphere comes from the 0:23:08.520 --> 0:23:12.440 burning of fossil fuels, So as we see the concentration decrease, 0:23:12.760 --> 0:23:16.240 we know that's because proportionally more carbon twelve is being 0:23:16.280 --> 0:23:19.720 released into the atmosphere, diluting the already tiny concentration of 0:23:19.760 --> 0:23:22.639 carbon fourteen. So that's useful for scientists who are studying 0:23:22.680 --> 0:23:27.280 climate change and pollution. But that's not exactly a happy story, 0:23:27.400 --> 0:23:32.000 is it. So what are our options if carbon dating 0:23:32.160 --> 0:23:36.040 becomes unreliable. Well, that depends on what you're trying to analyze. 0:23:36.400 --> 0:23:39.640 If you're looking at inorganic stuff like rocks, you don't 0:23:39.640 --> 0:23:41.639 need to use carbon fourteen in the first place. That 0:23:41.640 --> 0:23:44.520 would be pretty much useless. You would use something else 0:23:44.520 --> 0:23:48.040 like potassium argon dating, which is useful to estimate the 0:23:48.040 --> 0:23:50.400 age of rocks that are a hundred thousand years old 0:23:50.520 --> 0:23:52.920 or younger. And if that's not a big enough range, 0:23:52.960 --> 0:23:56.200 you can actually use uranium lead dating and that will 0:23:56.280 --> 0:23:59.320 let you estimate rocks between one point four and five 0:23:59.480 --> 0:24:03.000 million years old. There's a lot of different options if 0:24:03.000 --> 0:24:05.840 you're trying to date stuff. When it comes to organic materials, however, 0:24:05.880 --> 0:24:09.159 it's a lot more tricky. Radio carbon was a great tool, 0:24:10.119 --> 0:24:13.440 but if it becomes unreliable. We're gonna have to use 0:24:13.520 --> 0:24:19.160 other methods like contextual clues and other items that are 0:24:19.160 --> 0:24:23.960 helping us connect things to dates. So this is a 0:24:24.000 --> 0:24:27.880 big problem. I guess you could argue that's a big 0:24:27.920 --> 0:24:31.800 problem for future generations. And perhaps the records we leave 0:24:31.880 --> 0:24:39.840 behind now are so uh so complete, they're so voluminous, 0:24:39.880 --> 0:24:43.120 I guess is the best word that future generations will 0:24:43.160 --> 0:24:46.840 likely have more than enough material to determine when something 0:24:47.280 --> 0:24:52.040 originated from our time versus earlier times. But the point 0:24:52.080 --> 0:24:56.119 being that the way we're interacting with our world is 0:24:56.240 --> 0:25:01.800 changing this fundamental ratio of carbon fourteen to carbon twelve, 0:25:02.560 --> 0:25:06.920 and that means that a really brilliant means of determining 0:25:06.920 --> 0:25:10.280