WEBVTT - How Did Hazardous Nuclear Testing Help Science?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff,

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<v Speaker 1>Lauren Vogel. Bomb here as wild as it seems to

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<v Speaker 1>us today. There was a time when the United States,

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<v Speaker 1>the Soviet Union, and other countries tested nuclear weapons by

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<v Speaker 1>exploding them right in Earth's atmosphere. From nineteen forty five

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<v Speaker 1>to nineteen sixty three, when such tests were finally banned

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<v Speaker 1>by an international treaty, more than five hundred nuclear bombs

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<v Speaker 1>were detonated, releasing radioactive fallout that spread far and wide

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<v Speaker 1>across the planet, causing harm to the environment and human health.

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<v Speaker 1>For example, everyone who's lived in the US after nineteen

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<v Speaker 1>fifty one has been exposed to nuclear fallout, and for

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<v Speaker 1>some it's resulted in an increased risk of thyroid cancer

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<v Speaker 1>according to the CDC. But for scientists, that fallout has

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<v Speaker 1>also provided an important measuring tool. The test caused a

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<v Speaker 1>spike in the atmospheric concentration of carbon fourteen, which is

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<v Speaker 1>an isotope or form of carbon that's radioactive but also

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<v Speaker 1>occurs naturally, just not usually in such a blump sum.

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<v Speaker 1>The excess carbon fourteen was distributed throughout Earth's atmosphere, peaking

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<v Speaker 1>in nineteen sixty three when the test ban went into effect.

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<v Speaker 1>This spike is called the carbon fourteen bomb pulse. That radioactivity,

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<v Speaker 1>which has gradually been declining since the nineteen sixties, has

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<v Speaker 1>been absorbed by plants, animals, and people, creating a sort

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<v Speaker 1>of time stamp that's enabled researchers to measure when things

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<v Speaker 1>have occurred, from the lifespan of white sharks to the

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<v Speaker 1>growth of human knee cartilage and even brain cells. It's

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<v Speaker 1>enabled forensic investigators to estimate the age and year of

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<v Speaker 1>death for human remains with much greater precision than was

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<v Speaker 1>previously possible. Okay, let's talk about how radiocarbon dating works,

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<v Speaker 1>because using the bomb pulse to date living or previously

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<v Speaker 1>living tissue is an advancement from the conventional radiocarbon dating

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<v Speaker 1>that uses naturally occurring carbon fourteen before the article. This

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<v Speaker 1>episode is based on How Stuff Works. Spoke via email

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<v Speaker 1>with Thomas D. Holland, a research professor and the director

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<v Speaker 1>of the Forensic Institute for Research and Education at Middle

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<v Speaker 1>Tennessee State University. He explained radiocarbon dating has long been

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<v Speaker 1>a mainstay of archaeologists. All living things absorb carbon during life.

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<v Speaker 1>This includes the most common form of the atom carbon twelve,

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<v Speaker 1>as well as the radioactive form carbon fourteen, and now

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<v Speaker 1>these two isotopic forms exist in a known ratio which

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<v Speaker 1>is reflected in the carbon in the tissues of living things.

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<v Speaker 1>When an organism dies, it stops taking in carbon, and

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<v Speaker 1>the atoms of carbon fourteen, which are unstable, will start

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<v Speaker 1>to decay at a predictable rate. They have a half

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<v Speaker 1>life of approximately fivey seven hundred years. A carbon twelve, meanwhile,

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<v Speaker 1>is stable, so the more time that passes, the more

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<v Speaker 1>the ratio of carbon fourteen to carbon twelve will decline.

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<v Speaker 1>So by measuring that ratio you can put a fairly

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<v Speaker 1>accurate date on when any given organism stop taking in carbon.

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<v Speaker 1>The big limitation of radiocarbon dating has always been the

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<v Speaker 1>error range. Holland said. Estimated dates derived from the radioactive

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<v Speaker 1>decay of carbon fourteen have a plus minus error range

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<v Speaker 1>based on the size and quality of the sample. Generally,

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<v Speaker 1>error ranges for a good sample are no more than

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<v Speaker 1>a few hundred years, which for most archaeological purposes is insignificant,

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<v Speaker 1>a rendering carbon dating a valuable tool in the archaeological toolkit.

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<v Speaker 1>This error range problem, however, it does present a real

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<v Speaker 1>limitation when the material being dated may be less than

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<v Speaker 1>one hundred years old. For example, human remains found buried

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<v Speaker 1>somewhere or recovered from a lake. Holland said, a skeleton

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<v Speaker 1>found buried in the woods may be a recent murder victim,

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<v Speaker 1>or they may represent an early settler to the area.

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<v Speaker 1>Traditional radiocarbon dating may allow for a point estimate of

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<v Speaker 1>the person's year of death, but if it's accompanied by

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<v Speaker 1>a plus minus error range of two hundred years, it

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<v Speaker 1>renders the estimate of little use, at least in forensic contexts.

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<v Speaker 1>But this is where the bomb pulse comes in. The

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<v Speaker 1>amount of naturally occurring carbon fourteen in our atmosphere is

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<v Speaker 1>relatively constant because it's created by cosmic radiations striking our

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<v Speaker 1>atmosphere relatively constantly. The bomb pulse, though, is not constant.

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<v Speaker 1>Holland said. In the thirteen years that above ground nuclear

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<v Speaker 1>bomb tests were conducted, did the relative amount of carbon

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<v Speaker 1>fourteen in the atmosphere almost doubled the normal level. Viewed

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<v Speaker 1>on a longitudinal chart, the total amount of carbon fourteen

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<v Speaker 1>present in the atmosphere shows a dramatic pulse in late

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<v Speaker 1>nineteen sixty three, followed by a gradual decline of approximately

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<v Speaker 1>four percent a year as the artificial bomb created carbon

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<v Speaker 1>fourteen is absorbed out of the atmosphere by living things

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<v Speaker 1>and the ocean. That means that if a skeleton found

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<v Speaker 1>in the woods doesn't show the presence of large amounts

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<v Speaker 1>of carbon fourteen, that's a pretty good indication that it

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<v Speaker 1>dates from before nineteen fifty. But if there's evidence of

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<v Speaker 1>the bomb pulse's effects, then the bones probably belong to

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<v Speaker 1>a person who died sometime between nineteen fifty and the present.

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<v Speaker 1>But wait, there's more, Holland said. Additionally, because the graph

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<v Speaker 1>of atmosphere carbon fourteen shows a sharp upward slope beginning

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<v Speaker 1>with the first nuclear bomb test in nineteen fifty, peaking

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<v Speaker 1>in late nineteen sixty three when the test ban Treaty

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<v Speaker 1>was signed, and then a more gradual absorption curve continuing

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<v Speaker 1>into the present, it may be possible to fine tune

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<v Speaker 1>the date of death for individuals who died post nineteen

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<v Speaker 1>fifty By examining tissues with different growth and turnover rates,

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<v Speaker 1>such as fingernails and hair relative to bone, Scientists can

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<v Speaker 1>estimate where on the bomb pulse downward slope the sample

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<v Speaker 1>falls and speculate a more exact age. Holland explained tissues

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<v Speaker 1>that remodel slowly, such as bone, which may take years

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<v Speaker 1>to turnover, will reflect the higher concentration of bomb carbon

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<v Speaker 1>fourteen than will tissues such as hair, which will reflect

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<v Speaker 1>carbon fourteen absorbed closer to the time of death and

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<v Speaker 1>therefore lower on the declining slope. This can result in

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<v Speaker 1>estimates of year of death within one to five years,

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<v Speaker 1>and those estimates are pretty accurate. Study found that the

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<v Speaker 1>carbon fourteen levels and fingernails can help scientists determine the

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<v Speaker 1>year of death within ninety one percent accuracy, and the

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<v Speaker 1>bomb pulse isn't just useful for dating human bodies. Researchers

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<v Speaker 1>have also used the bomb pulse to study the ages

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<v Speaker 1>of ivory seized from the ivory trade to determine whether

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<v Speaker 1>it's antique or from recent poaching, and to measure the

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<v Speaker 1>time period between when a coca leaf was harvested in

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<v Speaker 1>South America and the cocaine made from it was seized

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<v Speaker 1>in the United States. And oceanographers have used carbon to

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<v Speaker 1>determine how the oceans are absorbing carbon dioxide. The main

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<v Speaker 1>problem for scientists is that the bomb pulse will only

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<v Speaker 1>be useful for tracking dates within a narrow time window.

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<v Speaker 1>Holland said the bomb pulse will run its course by

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<v Speaker 1>approximately twenty thirty and carbon fourteen levels will return to

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<v Speaker 1>their pre nineteen fifty level, So we'll have to come

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<v Speaker 1>up with other ways of more exact dating in the future.

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<v Speaker 1>And on that note, I'll leave you with an old joke.

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<v Speaker 1>If it weren't for carbon fourteen, I wouldn't date at all.

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<v Speaker 1>Today's episode is based on the article the Surprising silver

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<v Speaker 1>Lining of the Atomic Age nuclear tests on how stuffworks

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<v Speaker 1>dot Com, written by Patrick J. Khider. Brain Stuff is

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<v Speaker 1>production of iHeartRadio in partnership with HowStuffWorks dot Com and

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<v Speaker 1>is produced by Tyler Klang. Four more podcasts my heart Radio,

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<v Speaker 1>visit the iHeartRadio app, Apple Podcasts, or wherever you listen

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