1 00:00:01,840 --> 00:00:07,400 Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff, 2 00:00:07,440 --> 00:00:11,520 Speaker 1: Lauren Vogel. Bomb here as wild as it seems to 3 00:00:11,600 --> 00:00:14,480 Speaker 1: us today. There was a time when the United States, 4 00:00:14,600 --> 00:00:18,600 Speaker 1: the Soviet Union, and other countries tested nuclear weapons by 5 00:00:18,800 --> 00:00:23,599 Speaker 1: exploding them right in Earth's atmosphere. From nineteen forty five 6 00:00:23,640 --> 00:00:26,960 Speaker 1: to nineteen sixty three, when such tests were finally banned 7 00:00:26,960 --> 00:00:30,720 Speaker 1: by an international treaty, more than five hundred nuclear bombs 8 00:00:30,720 --> 00:00:34,840 Speaker 1: were detonated, releasing radioactive fallout that spread far and wide 9 00:00:34,880 --> 00:00:38,440 Speaker 1: across the planet, causing harm to the environment and human health. 10 00:00:39,640 --> 00:00:43,080 Speaker 1: For example, everyone who's lived in the US after nineteen 11 00:00:43,159 --> 00:00:47,159 Speaker 1: fifty one has been exposed to nuclear fallout, and for 12 00:00:47,280 --> 00:00:50,680 Speaker 1: some it's resulted in an increased risk of thyroid cancer 13 00:00:50,800 --> 00:00:56,480 Speaker 1: according to the CDC. But for scientists, that fallout has 14 00:00:56,520 --> 00:01:00,760 Speaker 1: also provided an important measuring tool. The test caused a 15 00:01:00,840 --> 00:01:05,160 Speaker 1: spike in the atmospheric concentration of carbon fourteen, which is 16 00:01:05,200 --> 00:01:09,080 Speaker 1: an isotope or form of carbon that's radioactive but also 17 00:01:09,160 --> 00:01:12,959 Speaker 1: occurs naturally, just not usually in such a blump sum. 18 00:01:13,520 --> 00:01:17,800 Speaker 1: The excess carbon fourteen was distributed throughout Earth's atmosphere, peaking 19 00:01:17,800 --> 00:01:21,000 Speaker 1: in nineteen sixty three when the test ban went into effect. 20 00:01:21,760 --> 00:01:28,759 Speaker 1: This spike is called the carbon fourteen bomb pulse. That radioactivity, 21 00:01:28,920 --> 00:01:32,600 Speaker 1: which has gradually been declining since the nineteen sixties, has 22 00:01:32,680 --> 00:01:37,160 Speaker 1: been absorbed by plants, animals, and people, creating a sort 23 00:01:37,200 --> 00:01:41,160 Speaker 1: of time stamp that's enabled researchers to measure when things 24 00:01:41,160 --> 00:01:44,720 Speaker 1: have occurred, from the lifespan of white sharks to the 25 00:01:44,760 --> 00:01:49,040 Speaker 1: growth of human knee cartilage and even brain cells. It's 26 00:01:49,120 --> 00:01:52,600 Speaker 1: enabled forensic investigators to estimate the age and year of 27 00:01:52,640 --> 00:01:55,960 Speaker 1: death for human remains with much greater precision than was 28 00:01:56,040 --> 00:02:03,320 Speaker 1: previously possible. Okay, let's talk about how radiocarbon dating works, 29 00:02:03,680 --> 00:02:07,400 Speaker 1: because using the bomb pulse to date living or previously 30 00:02:07,440 --> 00:02:11,480 Speaker 1: living tissue is an advancement from the conventional radiocarbon dating 31 00:02:11,639 --> 00:02:17,240 Speaker 1: that uses naturally occurring carbon fourteen before the article. This 32 00:02:17,280 --> 00:02:20,040 Speaker 1: episode is based on How Stuff Works. Spoke via email 33 00:02:20,160 --> 00:02:23,840 Speaker 1: with Thomas D. Holland, a research professor and the director 34 00:02:23,880 --> 00:02:26,800 Speaker 1: of the Forensic Institute for Research and Education at Middle 35 00:02:26,840 --> 00:02:32,359 Speaker 1: Tennessee State University. He explained radiocarbon dating has long been 36 00:02:32,400 --> 00:02:37,239 Speaker 1: a mainstay of archaeologists. All living things absorb carbon during life. 37 00:02:37,600 --> 00:02:40,960 Speaker 1: This includes the most common form of the atom carbon twelve, 38 00:02:41,320 --> 00:02:46,640 Speaker 1: as well as the radioactive form carbon fourteen, and now 39 00:02:46,720 --> 00:02:50,640 Speaker 1: these two isotopic forms exist in a known ratio which 40 00:02:50,720 --> 00:02:54,000 Speaker 1: is reflected in the carbon in the tissues of living things. 41 00:02:54,720 --> 00:02:58,160 Speaker 1: When an organism dies, it stops taking in carbon, and 42 00:02:58,320 --> 00:03:01,639 Speaker 1: the atoms of carbon fourteen, which are unstable, will start 43 00:03:01,680 --> 00:03:04,560 Speaker 1: to decay at a predictable rate. They have a half 44 00:03:04,600 --> 00:03:09,600 Speaker 1: life of approximately fivey seven hundred years. A carbon twelve, meanwhile, 45 00:03:09,760 --> 00:03:13,640 Speaker 1: is stable, so the more time that passes, the more 46 00:03:13,720 --> 00:03:17,520 Speaker 1: the ratio of carbon fourteen to carbon twelve will decline. 47 00:03:18,280 --> 00:03:20,840 Speaker 1: So by measuring that ratio you can put a fairly 48 00:03:20,880 --> 00:03:24,800 Speaker 1: accurate date on when any given organism stop taking in carbon. 49 00:03:27,000 --> 00:03:30,000 Speaker 1: The big limitation of radiocarbon dating has always been the 50 00:03:30,200 --> 00:03:35,360 Speaker 1: error range. Holland said. Estimated dates derived from the radioactive 51 00:03:35,400 --> 00:03:38,880 Speaker 1: decay of carbon fourteen have a plus minus error range 52 00:03:38,960 --> 00:03:43,080 Speaker 1: based on the size and quality of the sample. Generally, 53 00:03:43,400 --> 00:03:46,240 Speaker 1: error ranges for a good sample are no more than 54 00:03:46,280 --> 00:03:51,000 Speaker 1: a few hundred years, which for most archaeological purposes is insignificant, 55 00:03:51,320 --> 00:03:55,360 Speaker 1: a rendering carbon dating a valuable tool in the archaeological toolkit. 56 00:03:57,800 --> 00:04:01,200 Speaker 1: This error range problem, however, it does present a real 57 00:04:01,240 --> 00:04:04,560 Speaker 1: limitation when the material being dated may be less than 58 00:04:04,560 --> 00:04:08,360 Speaker 1: one hundred years old. For example, human remains found buried 59 00:04:08,400 --> 00:04:13,120 Speaker 1: somewhere or recovered from a lake. Holland said, a skeleton 60 00:04:13,200 --> 00:04:16,440 Speaker 1: found buried in the woods may be a recent murder victim, 61 00:04:16,720 --> 00:04:19,520 Speaker 1: or they may represent an early settler to the area. 62 00:04:20,240 --> 00:04:23,720 Speaker 1: Traditional radiocarbon dating may allow for a point estimate of 63 00:04:23,760 --> 00:04:26,960 Speaker 1: the person's year of death, but if it's accompanied by 64 00:04:27,000 --> 00:04:30,280 Speaker 1: a plus minus error range of two hundred years, it 65 00:04:30,279 --> 00:04:34,919 Speaker 1: renders the estimate of little use, at least in forensic contexts. 66 00:04:36,480 --> 00:04:40,400 Speaker 1: But this is where the bomb pulse comes in. The 67 00:04:40,440 --> 00:04:43,880 Speaker 1: amount of naturally occurring carbon fourteen in our atmosphere is 68 00:04:43,920 --> 00:04:47,960 Speaker 1: relatively constant because it's created by cosmic radiations striking our 69 00:04:48,000 --> 00:04:53,400 Speaker 1: atmosphere relatively constantly. The bomb pulse, though, is not constant. 70 00:04:54,600 --> 00:04:58,880 Speaker 1: Holland said. In the thirteen years that above ground nuclear 71 00:04:58,920 --> 00:05:01,920 Speaker 1: bomb tests were conducted, did the relative amount of carbon 72 00:05:01,960 --> 00:05:06,000 Speaker 1: fourteen in the atmosphere almost doubled the normal level. Viewed 73 00:05:06,040 --> 00:05:09,039 Speaker 1: on a longitudinal chart, the total amount of carbon fourteen 74 00:05:09,200 --> 00:05:12,480 Speaker 1: present in the atmosphere shows a dramatic pulse in late 75 00:05:12,560 --> 00:05:16,720 Speaker 1: nineteen sixty three, followed by a gradual decline of approximately 76 00:05:16,720 --> 00:05:20,599 Speaker 1: four percent a year as the artificial bomb created carbon 77 00:05:20,640 --> 00:05:23,960 Speaker 1: fourteen is absorbed out of the atmosphere by living things 78 00:05:24,080 --> 00:05:29,440 Speaker 1: and the ocean. That means that if a skeleton found 79 00:05:29,480 --> 00:05:32,400 Speaker 1: in the woods doesn't show the presence of large amounts 80 00:05:32,400 --> 00:05:35,600 Speaker 1: of carbon fourteen, that's a pretty good indication that it 81 00:05:35,720 --> 00:05:39,839 Speaker 1: dates from before nineteen fifty. But if there's evidence of 82 00:05:39,839 --> 00:05:43,160 Speaker 1: the bomb pulse's effects, then the bones probably belong to 83 00:05:43,200 --> 00:05:46,400 Speaker 1: a person who died sometime between nineteen fifty and the present. 84 00:05:47,600 --> 00:05:52,279 Speaker 1: But wait, there's more, Holland said. Additionally, because the graph 85 00:05:52,360 --> 00:05:56,560 Speaker 1: of atmosphere carbon fourteen shows a sharp upward slope beginning 86 00:05:56,600 --> 00:05:59,719 Speaker 1: with the first nuclear bomb test in nineteen fifty, peaking 87 00:05:59,800 --> 00:06:02,400 Speaker 1: in late nineteen sixty three when the test ban Treaty 88 00:06:02,440 --> 00:06:05,920 Speaker 1: was signed, and then a more gradual absorption curve continuing 89 00:06:05,960 --> 00:06:09,159 Speaker 1: into the present, it may be possible to fine tune 90 00:06:09,400 --> 00:06:12,520 Speaker 1: the date of death for individuals who died post nineteen 91 00:06:12,600 --> 00:06:19,120 Speaker 1: fifty By examining tissues with different growth and turnover rates, 92 00:06:19,200 --> 00:06:23,400 Speaker 1: such as fingernails and hair relative to bone, Scientists can 93 00:06:23,520 --> 00:06:27,160 Speaker 1: estimate where on the bomb pulse downward slope the sample 94 00:06:27,240 --> 00:06:33,520 Speaker 1: falls and speculate a more exact age. Holland explained tissues 95 00:06:33,560 --> 00:06:36,760 Speaker 1: that remodel slowly, such as bone, which may take years 96 00:06:36,760 --> 00:06:40,680 Speaker 1: to turnover, will reflect the higher concentration of bomb carbon 97 00:06:40,720 --> 00:06:44,320 Speaker 1: fourteen than will tissues such as hair, which will reflect 98 00:06:44,320 --> 00:06:47,479 Speaker 1: carbon fourteen absorbed closer to the time of death and 99 00:06:47,560 --> 00:06:51,400 Speaker 1: therefore lower on the declining slope. This can result in 100 00:06:51,520 --> 00:06:54,480 Speaker 1: estimates of year of death within one to five years, 101 00:06:56,160 --> 00:07:01,039 Speaker 1: and those estimates are pretty accurate. Study found that the 102 00:07:01,160 --> 00:07:04,720 Speaker 1: carbon fourteen levels and fingernails can help scientists determine the 103 00:07:04,800 --> 00:07:09,760 Speaker 1: year of death within ninety one percent accuracy, and the 104 00:07:09,760 --> 00:07:13,920 Speaker 1: bomb pulse isn't just useful for dating human bodies. Researchers 105 00:07:13,960 --> 00:07:16,400 Speaker 1: have also used the bomb pulse to study the ages 106 00:07:16,440 --> 00:07:19,960 Speaker 1: of ivory seized from the ivory trade to determine whether 107 00:07:20,000 --> 00:07:24,200 Speaker 1: it's antique or from recent poaching, and to measure the 108 00:07:24,240 --> 00:07:27,120 Speaker 1: time period between when a coca leaf was harvested in 109 00:07:27,160 --> 00:07:30,080 Speaker 1: South America and the cocaine made from it was seized 110 00:07:30,120 --> 00:07:34,360 Speaker 1: in the United States. And oceanographers have used carbon to 111 00:07:34,400 --> 00:07:39,760 Speaker 1: determine how the oceans are absorbing carbon dioxide. The main 112 00:07:39,800 --> 00:07:42,640 Speaker 1: problem for scientists is that the bomb pulse will only 113 00:07:42,720 --> 00:07:46,120 Speaker 1: be useful for tracking dates within a narrow time window. 114 00:07:47,080 --> 00:07:49,880 Speaker 1: Holland said the bomb pulse will run its course by 115 00:07:49,880 --> 00:07:53,920 Speaker 1: approximately twenty thirty and carbon fourteen levels will return to 116 00:07:53,960 --> 00:07:58,680 Speaker 1: their pre nineteen fifty level, So we'll have to come 117 00:07:58,760 --> 00:08:01,600 Speaker 1: up with other ways of more exact dating in the future. 118 00:08:02,960 --> 00:08:06,040 Speaker 1: And on that note, I'll leave you with an old joke. 119 00:08:06,840 --> 00:08:10,000 Speaker 1: If it weren't for carbon fourteen, I wouldn't date at all. 120 00:08:14,920 --> 00:08:17,880 Speaker 1: Today's episode is based on the article the Surprising silver 121 00:08:18,000 --> 00:08:20,800 Speaker 1: Lining of the Atomic Age nuclear tests on how stuffworks 122 00:08:20,800 --> 00:08:23,680 Speaker 1: dot Com, written by Patrick J. Khider. Brain Stuff is 123 00:08:23,680 --> 00:08:26,600 Speaker 1: production of iHeartRadio in partnership with HowStuffWorks dot Com and 124 00:08:26,680 --> 00:08:30,119 Speaker 1: is produced by Tyler Klang. Four more podcasts my heart Radio, 125 00:08:30,360 --> 00:08:33,400 Speaker 1: visit the iHeartRadio app, Apple Podcasts, or wherever you listen 126 00:08:33,440 --> 00:08:34,439 Speaker 1: to your favorite shows.