WEBVTT - Is Carbon Dating on the way out? 0:00:04.360 --> 0:00:12.520 Get in Touch with Technology? What textfrom hofks dot com. 0:00:12.520 --> 0:00:16.080 Hey there, and welcome to text UFF. I'm Jonathan Strickland, 0:00:16.239 --> 0:00:21.000 your beloved host, and I'm on my own today. So uh, 0:00:21.200 --> 0:00:24.320 I will not be throwing it over to anybody because 0:00:24.800 --> 0:00:26.680 they won't be able to talk because they won't be here, 0:00:26.840 --> 0:00:29.160 as opposed to the normal reason where I just talk 0:00:29.280 --> 0:00:32.479 over them. So today I wanted to talk about something 0:00:32.479 --> 0:00:35.040 that was sent in as a listener request. In fact, 0:00:35.040 --> 0:00:38.720 this was sent in over Twitter, and uh, this comes 0:00:38.760 --> 0:00:42.960 from nikkil Cardale, and I do apologize that I'm sure 0:00:43.000 --> 0:00:46.960 I mispronounced your name, but uh, the request was could 0:00:47.000 --> 0:00:50.880 you do an episode explaining this carbon dating is pretty useful? 0:00:50.920 --> 0:00:56.680 So this effect seems relevant and uh Cardale actually uh 0:00:57.200 --> 0:01:01.360 commented on and and included another tweet from real scientists 0:01:01.400 --> 0:01:05.200 that included an article titled will our fossil use ruin 0:01:05.360 --> 0:01:08.400 our ability to use carbon dating as a scientific tool? 0:01:09.400 --> 0:01:13.440 This is really fascinating the idea of using carbon dating, uh, 0:01:13.440 --> 0:01:18.480 and how that that method might be in jeopardy because 0:01:18.840 --> 0:01:21.760 of the use of fossil fuels. So I thought I 0:01:21.760 --> 0:01:25.319 would go into that explain what carbon dating is and 0:01:25.440 --> 0:01:28.880 why it might not be an accurate means of telling 0:01:28.880 --> 0:01:33.320 how old something is after too long. So going into 0:01:33.360 --> 0:01:36.040 the article, it's about how the enormous amount of carbon 0:01:36.080 --> 0:01:39.320 emissions we generate could make carbon dating and unreliable means 0:01:39.360 --> 0:01:42.720 to determine the age of certain types of materials. But 0:01:42.840 --> 0:01:45.800 to understand how that's possible, we need to know how 0:01:45.920 --> 0:01:50.400 carbon dating works first, So we're gonna do a carbon 0:01:50.480 --> 0:01:53.360 dating one oh one. Now, the first thing that we 0:01:53.400 --> 0:01:57.840 have to talk about is carbon fourteen. So the fourteen 0:01:58.160 --> 0:02:01.360 in carbon fourteen tells us it's an isotope of carbon. 0:02:02.080 --> 0:02:06.120 This particular isotope must have eight neutrons because carbon has 0:02:06.160 --> 0:02:09.640 six protons. You can change the number of neutrons in 0:02:09.680 --> 0:02:13.560 an atom. That's the different types of isotopes atoms may have, 0:02:13.919 --> 0:02:16.680 But you can't change the number of protons and atom 0:02:16.760 --> 0:02:20.200 has without changing that element. So carbon has six protons, 0:02:20.440 --> 0:02:22.480 and if you change that number of protons, you change 0:02:22.480 --> 0:02:27.040 the element itself. It acts reacts differently in chemical operations, 0:02:27.639 --> 0:02:32.440 and uh is no longer carbon. So carbon twelve is 0:02:32.520 --> 0:02:36.200 the most common form of carbon that we find. It 0:02:36.280 --> 0:02:39.560 has six protons and six neutrons. Then you have carbon thirteen, 0:02:39.600 --> 0:02:42.200 which is six protons and seven neutrons, and both of 0:02:42.200 --> 0:02:46.400 those are stable forms of carbon. That means they don't decay. 0:02:46.560 --> 0:02:49.680 So if you have carbon twelve or carbon thirteen, you 0:02:49.720 --> 0:02:52.200 put it in a box and you leave for I 0:02:52.240 --> 0:02:55.240 don't know, two billion years, and you come back, you're 0:02:55.240 --> 0:02:58.320 still gonna have carbon twelve or carbon thirteen because they 0:02:58.320 --> 0:03:02.280 remain stable they do not decay. But carbon fourteen is different. 0:03:02.560 --> 0:03:07.920 It is a radio isotope. Radioisotopes are also known as 0:03:08.080 --> 0:03:12.680 radio nucleides, and these are isotopes of a particular atom 0:03:12.800 --> 0:03:16.919 that have an unstable nucleus. These isotopes undergo what we 0:03:17.000 --> 0:03:20.480 call nuclear decay, and in that process they release some 0:03:20.560 --> 0:03:24.320 excess energy in the form of stuff like gamma rays 0:03:24.360 --> 0:03:28.960 and or subatomic particles. Carbon fourteen undergoes what is called 0:03:29.360 --> 0:03:33.480 beta decay. So when it decays, one of the neutrons 0:03:33.480 --> 0:03:37.920 in the nucleus spontaneously changes into a proton, an electron, 0:03:38.280 --> 0:03:42.160 and an anti neutrino. The nucleus gives the boot to 0:03:42.200 --> 0:03:46.040 the electron and the anti neutrino, but the proton stays behind, 0:03:46.120 --> 0:03:49.480 which means the atom no longer is a carbon atom. 0:03:49.520 --> 0:03:52.720 Since again we mentioned that atoms depend upon the number 0:03:52.720 --> 0:03:56.520 of protons, and the nucleus. So the carbon fourteen decays 0:03:56.600 --> 0:04:02.320 into nitrogen fourteen, and nitrogen fourteen has seven protons and 0:04:02.440 --> 0:04:05.440 seven neutrons. Also, by the way, one of the few 0:04:05.680 --> 0:04:09.520 stable elements that has both an odd number of protons 0:04:09.600 --> 0:04:13.880 and an odd number of neutrons uh, and nitrogen fourteen 0:04:14.040 --> 0:04:17.240 is stable. It makes up the vast majority of the 0:04:17.320 --> 0:04:21.960 nitrogen found naturally unearthed, More than of the nitrogen found 0:04:22.000 --> 0:04:26.560 on Earth is nitrogen fourteen. So radioactive decay occurs naturally 0:04:26.680 --> 0:04:30.400 within these isotopes, and it's a spontaneous occurrence. That's really 0:04:30.440 --> 0:04:34.119 important to remember. Carbon fourteen has a radioactive half life 0:04:34.160 --> 0:04:39.039 of about five thousand, seven hundred years. There's some confusion 0:04:39.080 --> 0:04:41.479 about what that means. I find in day to day 0:04:41.520 --> 0:04:44.159 conversations with people who haven't had science in a while. 0:04:44.400 --> 0:04:47.400 You guys who have recently had this in science class, 0:04:47.440 --> 0:04:50.080 you're rolling your eyes right now. But for adults who 0:04:50.120 --> 0:04:52.679 have not taken a science class in a long time, 0:04:53.000 --> 0:04:57.440 this might require some some refreshing. So half life of 0:04:57.480 --> 0:05:00.800 five thousand, seven hundred years, what does that mean? It 0:05:00.839 --> 0:05:03.760 means if you have a given amount of carbon fourteen 0:05:04.360 --> 0:05:08.160 after five thousand, seven hundred years or so, you'll have 0:05:08.520 --> 0:05:11.880 only half of that carbon fourteen remaining, the other half 0:05:12.040 --> 0:05:17.040 having undergone decay radioactive decay and turning into nitrogen. Now, 0:05:17.080 --> 0:05:19.520 this doesn't mean that all the carbon fourteen will be 0:05:19.560 --> 0:05:22.920 gone after another five thousand, seven hundred years, nor does 0:05:22.960 --> 0:05:25.919 it mean that carbon fourteen has a full life of 0:05:25.960 --> 0:05:29.160 eleven thousand, four hundred years or anything like that. In fact, 0:05:29.200 --> 0:05:32.320 what it really means is that after another five thousand, 0:05:32.360 --> 0:05:35.640 seven hundred years, half of the remaining sample will have decayed, 0:05:35.800 --> 0:05:38.080 leaving you with about a quarter of what you started with. 0:05:38.279 --> 0:05:40.640 And another five thousand, seven hundred years if that means 0:05:40.640 --> 0:05:42.720 you be left with about an eighth of that sample, 0:05:42.800 --> 0:05:47.279 and so on. Carbon fourteen exists naturally on Earth in 0:05:47.400 --> 0:05:51.039 trace amounts. Before the nineteen forties, the carbon fourteen on 0:05:51.080 --> 0:05:55.200 Earth was created through a natural process. Once in a while, 0:05:55.400 --> 0:05:59.159 cosmic rays, these very high energy particles in outer space, 0:05:59.400 --> 0:06:02.920 would collie with an atom in our atmosphere or upper atmosphere, 0:06:03.279 --> 0:06:05.839 and this collision would end up emitting a high energy 0:06:05.880 --> 0:06:09.839 neutron that then could collide with nitrogen atoms that are 0:06:09.880 --> 0:06:13.640 also way up there in our atmosphere. Now, cosmic rays 0:06:13.680 --> 0:06:17.520 are high energy sub atomic particles. They originate outside of 0:06:17.520 --> 0:06:21.920 our solar system. Usually they're emitted by supernova of massive stars, 0:06:22.240 --> 0:06:25.599 and these sub atomic particles are primarily atomic nuclei and 0:06:25.760 --> 0:06:28.880 high energy protons. So this collision of the high energy 0:06:28.920 --> 0:06:33.159 neutron with the nitrogen forces a proton to leave the 0:06:33.240 --> 0:06:37.440 nucleus and the in fourteen changes to C fourteen. So, 0:06:37.480 --> 0:06:40.120 in other words, nitrogen fourteen turns to carbon fourteen. So 0:06:40.160 --> 0:06:42.800 instead of having seven protons and seven neutrons, the new 0:06:42.800 --> 0:06:46.919 atom has six protons and eight neutrons. The proton that 0:06:47.000 --> 0:06:50.240 was broken off from the nucleus zooms off with an electron, 0:06:50.720 --> 0:06:53.159 so you get one proton and one electron. That means 0:06:53.200 --> 0:06:57.360 you have an atom of hydrogen. So again what's happening 0:06:57.440 --> 0:07:02.600 is a high energy neutron allignes with nitrogen fourteen, forces 0:07:02.680 --> 0:07:06.720 out a proton. The proton and an electron high tail 0:07:06.800 --> 0:07:11.560 it and honeymoon off as hydrogen, and the incoming neutron 0:07:12.200 --> 0:07:15.400 joins the party, and now you've got carbon fourteen. So 0:07:15.520 --> 0:07:19.360 pre nineteen forties, carbon fourteen is rare because of two reasons. 0:07:19.600 --> 0:07:23.600 It undergoes radioactive decay, so over time it disappears and 0:07:23.640 --> 0:07:26.160 it's produced by an event that's not super frequent, though 0:07:26.200 --> 0:07:30.400 it's also not uncommon, so it does happen regularly enough 0:07:30.480 --> 0:07:36.640 that carbon fourteen is replenished, but it's a very small 0:07:36.760 --> 0:07:41.040 overall percentage of the carbon here on Earth. Now, living 0:07:41.080 --> 0:07:45.360 things here on Earth absorb carbon through various means, and 0:07:45.440 --> 0:07:48.640 some of that carbon is carbon fourteen. So it may 0:07:48.760 --> 0:07:51.400 be that you know, you eat a plant and that 0:07:51.440 --> 0:07:53.480 plant has some of the carbon fourteen in it. Now 0:07:53.520 --> 0:07:55.960 you have some of the carbon fourteen and you And 0:07:56.000 --> 0:07:58.920 if we know the ratio of carbon fourteen to the 0:07:58.960 --> 0:08:02.640 stable form of carbon twelve, we can look at materials 0:08:02.640 --> 0:08:04.800 and analyze them to see how the ratio of carbon 0:08:04.840 --> 0:08:07.760 fourteen to carbon twelve in the material stacks up to 0:08:07.880 --> 0:08:11.600 the standard ratio With living things, this becomes a matter 0:08:11.600 --> 0:08:15.000 of looking at how much carbon fourteen is not there? 0:08:15.960 --> 0:08:19.520 All right, That's it's a little confusing. Let me explain. So, 0:08:19.680 --> 0:08:23.440 when a living thing is still alive, it accumulates carbon 0:08:23.520 --> 0:08:27.720 at about the same rate it loses carbon. So carbon 0:08:27.800 --> 0:08:31.600 cosmic rays produced this carbon fourteen frequently enough that the 0:08:31.720 --> 0:08:35.800 ratio between carbon fourteen and carbon twelve remains steady. So 0:08:35.840 --> 0:08:40.520 the percentage of carbon fourteen to carbon twelve is fairly standardized. 0:08:40.920 --> 0:08:44.160 But when a living thing stops being alive and turns 0:08:44.200 --> 0:08:49.880 into a not living anymore thing, it stops accumulating carbon, 0:08:50.280 --> 0:08:53.080 so it has the carbon that it has inside of 0:08:53.120 --> 0:08:57.080 it stays. That's it. You're not losing anymore. You're not 0:08:57.120 --> 0:09:02.160 gaining any more except for carbon fourteen because carbon fourteen 0:09:02.360 --> 0:09:06.920 undergoes radioactive decay, so over time, some of that carbon 0:09:07.000 --> 0:09:12.760 fourteen starts to convert to nitrogen. So that means if 0:09:12.800 --> 0:09:16.400 you can look at the remains of a living thing 0:09:17.000 --> 0:09:20.880 and detect the ratio of carbon fourteen to carbon twelve, 0:09:21.280 --> 0:09:23.600 you can get an idea of how long ago it 0:09:23.800 --> 0:09:26.920 was that it stopped taking in carbon, as in, how 0:09:26.920 --> 0:09:30.040 long ago was it that this lip once living thing died. 0:09:31.080 --> 0:09:33.079 It gets a little more complicated than all that, but 0:09:33.280 --> 0:09:37.440 here's the basic rule. If we want to be really precise, 0:09:37.880 --> 0:09:41.040 here's the equation we use to determine the age of 0:09:41.080 --> 0:09:44.960 a sample of material. You have an equation where you 0:09:45.000 --> 0:09:48.840 take the natural logarithm of n F divided by n 0:09:48.840 --> 0:09:52.720 o uh that in turn is divided by negative point 0:09:52.800 --> 0:09:55.679 six nine three, and then you multiply it by t 0:09:56.640 --> 0:10:01.679 uh one half, so one half t The natural logarithm 0:10:02.120 --> 0:10:05.640 is a specific logarithm applied to this equation and other 0:10:05.679 --> 0:10:08.199 things as well. N F divided way n O actually 0:10:08.760 --> 0:10:11.560 refers to the percentage of carbon fourteen and the sample 0:10:11.600 --> 0:10:15.640 compared to the amount found in living stuff today at 0:10:16.000 --> 0:10:18.679 times one half is the half life of carbon, so 0:10:18.720 --> 0:10:21.600 that's five thousand, seven hundred years. So it's a lot 0:10:21.880 --> 0:10:24.240 easier to understand this if we take a specific example. 0:10:25.200 --> 0:10:28.320 So let's say you've got a sample of some sort 0:10:28.400 --> 0:10:32.600 of material and you have determined that there is five 0:10:32.679 --> 0:10:35.760 percent of the amount of carbon fourteen in that material 0:10:36.400 --> 0:10:38.760 compared to what you would find in something that is 0:10:38.800 --> 0:10:42.200 alive right now, So you take a sample of a 0:10:42.240 --> 0:10:45.640 living thing, and then you take the sample of the 0:10:45.679 --> 0:10:48.200 thing you're testing. You see that the thing you're testing 0:10:48.240 --> 0:10:50.280 only has five percent of the carbon fourteen you would 0:10:50.280 --> 0:10:52.480 find in living things. That means you would fill out 0:10:52.520 --> 0:10:55.920 the equation with the natural logarithm of point zero five 0:10:56.640 --> 0:11:01.000 divided by negative point six nine three, and you multiply 0:11:01.080 --> 0:11:04.959 that that result to with five thousand, seven hundred years 0:11:05.120 --> 0:11:07.200 the natural logorithm at point zero five. By the way, 0:11:07.240 --> 0:11:09.199 in case you don't want to whip out your calculator 0:11:09.679 --> 0:11:12.959 is negative two point nine nine five seven three to 0:11:13.240 --> 0:11:16.440 two seven three five five. If you divide that by 0:11:16.520 --> 0:11:20.560 negative point six nine three, you get four point three 0:11:20.640 --> 0:11:25.720 to two eight four five night. Don't dial that number. 0:11:26.720 --> 0:11:29.760 If you take that number, the four point three, etcetera, 0:11:29.840 --> 0:11:32.480 and you multiply that by five thousand, seven hundred years, 0:11:32.920 --> 0:11:35.680 you end up with twenty four thousand, six hundred forty 0:11:35.760 --> 0:11:38.440 point two years, meaning the stuff you're looking at died 0:11:38.600 --> 0:11:42.360 somewhere around that time frame, give or take thirty two 0:11:42.480 --> 0:11:45.439 hundred years. So somewhere on twenty four thousand, six hundred 0:11:45.520 --> 0:11:49.600 forty years ago is when that thing no longer breathed 0:11:49.800 --> 0:11:53.480 or lived, or however you wanted to find it. By 0:11:53.480 --> 0:11:57.240 the way, this approach does have a limitation. Anything older 0:11:57.240 --> 0:11:59.800 than sixty thousand years is pretty much out of bounds. 0:12:00.200 --> 0:12:02.520 Carbon fourteen just isn't a reliable means of dating that 0:12:02.559 --> 0:12:05.240 sort of material, and we have to rely on other methods. 0:12:05.280 --> 0:12:08.960 So carbon fourteen, because of the decay once against two 0:12:09.200 --> 0:12:13.240 very small amounts, it's very difficult to narrow it down 0:12:13.280 --> 0:12:16.080 to a specific time, and if it's long enough, there 0:12:16.080 --> 0:12:18.360 won't be any carbon fourteen in at all. All the 0:12:18.400 --> 0:12:21.160 carbon fourteen will have decayed by then you can't use 0:12:21.240 --> 0:12:25.640 carbon dating if there's no carbon fourteen left. So to 0:12:25.720 --> 0:12:29.200 actually test the carbon fourteen concentration, you first have to 0:12:29.200 --> 0:12:32.840 take the sample, uh whatever object it might be. You 0:12:32.880 --> 0:12:36.200 have to remove part of it, and typically you would 0:12:36.200 --> 0:12:39.280 apply some chemicals to the material, usually a very strong 0:12:39.400 --> 0:12:42.880 acid wash and a strong base wash. That's to remove 0:12:43.400 --> 0:12:47.200 all the contaminating materials that could end up giving you 0:12:47.559 --> 0:12:51.080 false readings on carbon fourteen. Then you would burn the 0:12:51.160 --> 0:12:55.520 sample within a glass container to capture the carbon dioxide 0:12:55.600 --> 0:12:59.480 that is emitted when you burn the material, and then 0:12:59.520 --> 0:13:02.640 you would end allize the carbon dioxide to find out 0:13:02.679 --> 0:13:05.880 the concentration of carbon fourteen. So you can see that 0:13:05.960 --> 0:13:09.280 this approach has a big drawback. It ends up damaging 0:13:09.520 --> 0:13:12.000 whatever it is you are attempting to date in the 0:13:12.000 --> 0:13:15.640 first place. And that's why some particularly high valued items 0:13:15.679 --> 0:13:18.880 go without being tested, because the perception is that even 0:13:18.920 --> 0:13:22.640 a small sample of that original piece would be too 0:13:22.760 --> 0:13:27.320 much damage to to uh make on this item. So 0:13:27.800 --> 0:13:31.120 certain items are considered very precious and there's a big 0:13:31.160 --> 0:13:34.720 resistance to using carbon dating because by the definition, you're 0:13:34.760 --> 0:13:37.880 going to be damaging the material. Now there's several lines 0:13:37.880 --> 0:13:41.440 of research they are exploring possible non destructive means of 0:13:41.559 --> 0:13:46.520 using radiocarbon dating. There's one that uses plasma oxidation and 0:13:46.559 --> 0:13:50.080 the use of non destructive washes to clean samples of 0:13:50.120 --> 0:13:54.520 those contaminating humic acids, which would lead to errors if 0:13:54.520 --> 0:13:58.280 they remain behind, but those are still largely in the 0:13:58.320 --> 0:14:02.480 testing phase and aren't the common means of using carbon dating. Also, 0:14:02.880 --> 0:14:05.440 keep in mind that we use this method to estimate 0:14:05.480 --> 0:14:08.400 the date of things made from organic materials, like the 0:14:08.440 --> 0:14:12.520 Dead Sea scrolls, but this estimation is based upon when 0:14:12.559 --> 0:14:15.840 the materials were harvested, so, in other words, whenever the 0:14:15.880 --> 0:14:18.720 living thing that the materials came from stopped being alive, 0:14:19.880 --> 0:14:22.480 it doesn't tell us the date of when the artifact 0:14:22.520 --> 0:14:25.440 was actually produced. So it's possible that you could come 0:14:25.480 --> 0:14:29.320 across an artifact like a scroll and you use carbon 0:14:29.400 --> 0:14:32.440 dating on it and find out that the scroll material 0:14:33.080 --> 0:14:35.600 is two thousand years old, meaning two thousand years ago 0:14:36.320 --> 0:14:40.320 whatever the scroll was made out of stopped living, but 0:14:40.360 --> 0:14:44.160 it doesn't tell you about the contents written in the scroll. 0:14:44.320 --> 0:14:47.920 It's possible that the contents were added to the scroll 0:14:48.200 --> 0:14:52.760 much after the living thing stopped being alive. Still, it's 0:14:52.760 --> 0:14:54.920 a pretty good bet that the two are within the 0:14:54.960 --> 0:14:58.360 same neighborhood of time, rather than someone held onto blank 0:14:58.400 --> 0:15:01.640 scrolls for a few centuries before or finally jotting something down. 0:15:03.120 --> 0:15:05.520 All right, it's all this is cool, But how did 0:15:05.560 --> 0:15:08.800 we even figure out? Radio carbon dating would be a 0:15:08.880 --> 0:15:12.760 possible way of figuring out how old something is. Well. 0:15:12.800 --> 0:15:15.160 Some early discoveries were made in the nineteen thirties at 0:15:15.200 --> 0:15:19.120 the Lawrence Radiation Laboratory in Berkeley, and you probably remember 0:15:19.160 --> 0:15:21.560 that if you've been listening to tech stuff. It factored 0:15:21.560 --> 0:15:23.960 heavily into the discussion I had with Ben Bolan about 0:15:23.960 --> 0:15:30.040 the Manhattan Project. So Franz Curry, an American physicist, observed 0:15:30.080 --> 0:15:33.280 something really interesting when he irradiated a cloud of air 0:15:33.480 --> 0:15:37.600 in a cloud chamber. He used neutrons to uh to 0:15:37.720 --> 0:15:42.240 irradiate that cloud, and he saw proton recoil tracks that 0:15:42.280 --> 0:15:46.760 indicated something was losing protons. So he concluded that the 0:15:46.840 --> 0:15:50.720 neutrons that he was using were colliding with nitrogen fourteen 0:15:51.280 --> 0:15:54.040 and producing what was believed to be a form of 0:15:54.080 --> 0:15:57.520 carbon as a result. With hydrogen being the other product 0:15:57.560 --> 0:16:00.440 of this collision, his work was further expo or by 0:16:00.440 --> 0:16:05.480 physicists like Tom W. Bonner, W. M. Brubaker, W. J. Burcham, 0:16:05.760 --> 0:16:09.880 and Maurice gold Hauber. Now collectively, this laid the foundation 0:16:09.960 --> 0:16:12.960 for the simple equation of a high energy neutron plus 0:16:13.120 --> 0:16:18.240 nitrogen fourteen produces one hydrogen atom and one carbon fourteen atom. 0:16:18.360 --> 0:16:21.120 Then you had Enrico Fermi. We talked about him in 0:16:21.160 --> 0:16:24.440 the Manhattan Project, and his work showed that the cross 0:16:24.480 --> 0:16:27.600 section of a nitrogen fourteen atom was much larger than 0:16:27.600 --> 0:16:32.600 other materials, and that suggested that neutron and nitrogen collisions 0:16:32.640 --> 0:16:35.640 might happen fairly regularly in nature as long as there 0:16:35.680 --> 0:16:39.040 were a supply of high energy neutrons. Then you have 0:16:39.120 --> 0:16:41.880 a Serge Korf, who was a physicist who was born 0:16:41.880 --> 0:16:44.960 in Finland and whose family immigrated to the United States 0:16:45.000 --> 0:16:48.480 in the early twentieth century. He discovered the phenomenon that 0:16:48.720 --> 0:16:52.760 cosmic rays interact with atoms and produce high energy neutrons 0:16:52.800 --> 0:16:57.840 in the upper atmosphere. So Faremi's prediction and corpse observation 0:16:57.960 --> 0:17:02.400 we're starting to kind of coalesce here. The observations convinced 0:17:02.400 --> 0:17:06.440 scientists that the neutrons themselves were not cosmic rays, because 0:17:06.480 --> 0:17:09.560 the neutrons had a lifespan of just eighteen minutes, and 0:17:09.600 --> 0:17:12.840 therefore a neutron wouldn't be able to survive the long 0:17:12.920 --> 0:17:15.760 trip through space. They must have been something else first, 0:17:16.640 --> 0:17:18.880 So they said the neutrons had to be a byproduct 0:17:19.320 --> 0:17:22.639 of another interaction. A cosmic ray must be interacting with 0:17:22.760 --> 0:17:26.680 something in the atmosphere. That interaction caused this high energy 0:17:26.720 --> 0:17:30.040 neutron to be omitted, and Core hypothesized that these neutrons 0:17:30.080 --> 0:17:33.440 could then interact with nitrogen fourteen to produce carbon fourteen 0:17:33.520 --> 0:17:37.399 in the upper atmosphere. Now, it was Willard F. Libby 0:17:37.440 --> 0:17:40.000 who came up with the idea that since carbon fourteen 0:17:40.119 --> 0:17:42.439 is generated at a steady rate due to cosmic ray 0:17:42.480 --> 0:17:46.120 interactions in our atmosphere, you should be able to use 0:17:46.160 --> 0:17:49.760 it to measure how long something has been dead. Libby 0:17:49.760 --> 0:17:52.360 would measure the value of carbon fourteen's half life at 0:17:52.440 --> 0:17:55.360 five thousand, five hundred sixty eight years, give or take 0:17:55.440 --> 0:17:58.879 thirty years, which became known as the Libby half life, 0:17:59.160 --> 0:18:02.000 and Libby, him off, would be awarded the Nobel Prize 0:18:02.000 --> 0:18:06.159 in nineteen sixty for his work in radiocarbon dating. All right, 0:18:06.560 --> 0:18:08.919 so that's the history of radiocarbon dating and generally how 0:18:09.040 --> 0:18:12.640 radiocarbon dating works. So why is it in trouble or 0:18:12.680 --> 0:18:17.280 what could possibly be causing confusion with radiocarbon dating. Well, 0:18:17.320 --> 0:18:19.280 there are two big things we need to talk about, 0:18:19.840 --> 0:18:22.040 and one was one that I've alluded to a couple 0:18:22.040 --> 0:18:25.920 of times. I mentioned that, you know, pre nineteen forties 0:18:26.320 --> 0:18:29.000 you had a certain level of carbon fourteen that was 0:18:29.080 --> 0:18:33.840 pretty standard. But the nuclear age really messed things up 0:18:33.840 --> 0:18:37.040 for us. They made carbon fourteen dating a bit tricky. 0:18:37.119 --> 0:18:41.080 Starting in the nineteen forties, we began testing nuclear bombs. Now, 0:18:41.119 --> 0:18:44.320 these bombs released a lot of energy upon exploding, partly 0:18:44.320 --> 0:18:46.879 in the form of high energy neutrons. You can probably 0:18:46.880 --> 0:18:49.240 see where this is going. Some of those high energy 0:18:49.240 --> 0:18:53.240 neutrons ended up interacting with nitrogen fourteen atoms, which meant 0:18:53.240 --> 0:18:57.040 that it produced carbon fourteen atoms as a result. So 0:18:57.119 --> 0:19:01.399 the concentration of carbon fourteen in priest in the wake 0:19:01.880 --> 0:19:05.520 of nuclear bomb testing. So anything that died after the 0:19:05.600 --> 0:19:09.280 nineteen forties actually has a higher concentration of carbon fourteen 0:19:09.560 --> 0:19:12.760 than the stuff that died before the nineteen forties did 0:19:13.280 --> 0:19:16.720 even know at the time of death. According to Professor Nalini, 0:19:16.880 --> 0:19:20.439 not Khannie of the Evergreen State College. The nineteen fifties 0:19:20.440 --> 0:19:24.879 saw a one hundred percent spike in carbon fourteen coming 0:19:24.880 --> 0:19:28.720 into the atmosphere. In nineteen sixty three, the United States 0:19:28.760 --> 0:19:32.480 and Russia agreed to stop above ground nuclear testing, and 0:19:32.520 --> 0:19:35.280 the levels of carbon fourteen in the atmosphere gradually dropped 0:19:35.280 --> 0:19:37.800 down to their normal levels. But that means there's a 0:19:37.880 --> 0:19:41.480 blip in the carbon fourteen radar between the nineteen forties 0:19:41.520 --> 0:19:44.119 and nineteen sixty three. So if you put yourself in 0:19:44.119 --> 0:19:48.399 the shoes of a future archaeologist, radio carbon dating becomes 0:19:48.480 --> 0:19:51.879 unreliable because the levels of carbon fourteen could be deceptive. 0:19:52.119 --> 0:19:54.760 If the thing you're measuring died during the era of 0:19:54.840 --> 0:19:58.399 nuclear testing, it might appear to be younger than you 0:19:58.480 --> 0:20:01.800 thought because there's a higher concentration of carbon fourteen in 0:20:01.880 --> 0:20:05.639 its sample then you otherwise would have expected. So it 0:20:05.720 --> 0:20:10.240 may seem that something died in twenty fifteen as opposed 0:20:10.240 --> 0:20:14.480 to nineteen sixty three. That's just an example. Now to 0:20:14.560 --> 0:20:17.000 the article that prompted this episode in the first place, 0:20:17.440 --> 0:20:20.720 that's a different case. Researchers published a study in the 0:20:20.720 --> 0:20:23.760 Proceedings of the National Academy of Sciences about how the 0:20:23.840 --> 0:20:28.520 use of fossil fuels is further making radiocarbon dating less reliable. 0:20:29.080 --> 0:20:32.080 And this time it's not an excess of carbon fourteen. 0:20:32.119 --> 0:20:36.280 It's actually the opposite problem. Fossil fuels have no carbon 0:20:36.359 --> 0:20:40.439 fourteen in them because they are fossil fuels. This is 0:20:40.840 --> 0:20:44.280 billions of years old, so they're far too old for 0:20:44.320 --> 0:20:47.320 any carbon fourteen to remain. Remember that carbon fourteen is 0:20:47.400 --> 0:20:52.000 decaying over time and turning into nitrogen, so eventually all 0:20:52.040 --> 0:20:56.000 of those carbon fourteen atoms decay. So burning a fossil 0:20:56.040 --> 0:20:59.280 fuel create releases carbon dioxide, and the carbon in that 0:20:59.359 --> 0:21:02.119 CEO two has no carbon fourteen and it's all carbon 0:21:02.160 --> 0:21:05.800 twolve carbon thirteen. So the more fossil fuels we burn, 0:21:06.240 --> 0:21:09.720 the more we dilute the concentration of carbon fourteen that's 0:21:09.720 --> 0:21:13.280 in the atmosphere. So stuff from the nuclear age tends 0:21:13.320 --> 0:21:15.680 to look younger than it really is because of the 0:21:15.760 --> 0:21:19.400 higher concentration of carbon fourteen. Stuff from the later ages 0:21:19.520 --> 0:21:22.960 of fossil fuel use will look older than they really 0:21:23.000 --> 0:21:26.480 are because carbon fourteen has been deluded. So, according to 0:21:26.520 --> 0:21:30.520 the study, fresh organic material in twenty fifty would contain 0:21:30.560 --> 0:21:33.760 the same amount of carbon fourteen relative to carbon twelve 0:21:34.240 --> 0:21:38.320 as something dating from ten fifty, So you have a 0:21:38.440 --> 0:21:43.560 thousand years of doubt in any radio carbon dated samples. 0:21:44.560 --> 0:21:46.919 You would look at the two samples if you if 0:21:47.040 --> 0:21:50.480 all you had were miniscule samples of two things and 0:21:50.560 --> 0:21:53.600 one of them was a T shirt that was made 0:21:53.640 --> 0:21:57.040 in twenty fifty, and another was a piece of cloth 0:21:57.280 --> 0:22:00.159 that dated from ten fifty, and you did do you 0:22:00.240 --> 0:22:04.199 carbon dating, you'd get the same result. This is not 0:22:04.320 --> 0:22:07.080 good if you are trying to figure out how old 0:22:07.320 --> 0:22:11.760 something is. Heather Graven, who authored the study on fossil 0:22:11.800 --> 0:22:14.719 fuel emissions and the effect on radiocarbon dating, says that 0:22:14.760 --> 0:22:18.919 if we were to reduce carbon dioxide emissions drastically in 0:22:18.960 --> 0:22:22.720 the very near future, the effect on future radiocarbon dating 0:22:22.720 --> 0:22:26.040 would be equivalent to inserting a one year error on 0:22:26.119 --> 0:22:30.960 top of any estimation. If we don't drastically reduce emissions, 0:22:31.000 --> 0:22:34.680 that error range will continue to grow over time. One 0:22:34.720 --> 0:22:37.480 thing that the concentration of carbon fourteen tells us is 0:22:37.520 --> 0:22:40.040 how much carbon dioxide in the atmosphere comes from the 0:22:40.040 --> 0:22:43.960 burning of fossil fuels. So as we see the concentration decrease, 0:22:44.280 --> 0:22:47.760 we know that's because proportionally more carbon twelve is being 0:22:47.760 --> 0:22:51.240 released into the atmosphere, diluting the already tiny concentration of 0:22:51.240 --> 0:22:54.159 carbon fourteen. So that's useful for scientists who are studying 0:22:54.160 --> 0:22:58.760 climate change and pollution. But that's not exactly a happy story, 0:22:58.880 --> 0:23:03.480 is it. So what are our options if carbon dating 0:23:03.680 --> 0:23:07.560 becomes unreliable. Well, that depends on what you're trying to analyze. 0:23:07.880 --> 0:23:11.120 If you're looking at inorganic stuff like rocks, you don't 0:23:11.160 --> 0:23:13.119 need to use carbon fourteen in the first place. That 0:23:13.160 --> 0:23:16.000 would be pretty much useless. You would use something else 0:23:16.040 --> 0:23:19.560 like potassium argon dating, which is useful to estimate the 0:23:19.560 --> 0:23:21.920 age of rocks that are a hundred thousand years old 0:23:22.000 --> 0:23:24.440 or younger. And if that's not a big enough range, 0:23:24.480 --> 0:23:27.720 you can actually use uranium lead dating and that will 0:23:27.760 --> 0:23:30.840 let you estimate rocks between one point four and five 0:23:31.000 --> 0:23:34.480 million years old. There's a lot of different options if 0:23:34.520 --> 0:23:37.359 you're trying to date stuff. When it comes to organic materials, however, 0:23:37.400 --> 0:23:40.639 it's a lot more tricky. Radio carbon was a great tool, 0:23:41.600 --> 0:23:44.960 but if it becomes unreliable, we're gonna have to use 0:23:45.000 --> 0:23:50.200 other methods like contextual clues and other items that are 0:23:50.680 --> 0:23:55.480 helping us connect things to dates. So this is a 0:23:55.520 --> 0:23:59.400 big problem. I guess you could argue that's a big 0:23:59.440 --> 0:24:03.320 problem for future generations. And perhaps the records we leave 0:24:03.359 --> 0:24:11.280 behind now are so uh so complete, they're so voluminous, 0:24:11.359 --> 0:24:14.640 I guess is the best word, that future generations will 0:24:14.640 --> 0:24:18.320 likely have more than enough material to determine when something 0:24:18.800 --> 0:24:23.560 originated from our time versus earlier times. But the point 0:24:23.600 --> 0:24:27.639 being that the way we're interacting with our world is 0:24:27.760 --> 0:24:33.320 changing this fundamental ratio of carbon fourteen to carbon twelve, 0:24:34.080 --> 0:24:38.440 and that means that a really brilliant means of determining 0:24:38.440 --> 0:24:41.760