Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff,
Speaker 1: Lauren Vogel. Bomb here as wild as it seems to
Speaker 1: us today. There was a time when the United States,
Speaker 1: the Soviet Union, and other countries tested nuclear weapons by
Speaker 1: exploding them right in Earth's atmosphere. From nineteen forty five
Speaker 1: to nineteen sixty three, when such tests were finally banned
Speaker 1: by an international treaty, more than five hundred nuclear bombs
Speaker 1: were detonated, releasing radioactive fallout that spread far and wide
Speaker 1: across the planet, causing harm to the environment and human health.
Speaker 1: For example, everyone who's lived in the US after nineteen
Speaker 1: fifty one has been exposed to nuclear fallout, and for
Speaker 1: some it's resulted in an increased risk of thyroid cancer
Speaker 1: according to the CDC. But for scientists, that fallout has
Speaker 1: also provided an important measuring tool. The test caused a
Speaker 1: spike in the atmospheric concentration of carbon fourteen, which is
Speaker 1: an isotope or form of carbon that's radioactive but also
Speaker 1: occurs naturally, just not usually in such a blump sum.
Speaker 1: The excess carbon fourteen was distributed throughout Earth's atmosphere, peaking
Speaker 1: in nineteen sixty three when the test ban went into effect.
Speaker 1: This spike is called the carbon fourteen bomb pulse. That radioactivity,
Speaker 1: which has gradually been declining since the nineteen sixties, has
Speaker 1: been absorbed by plants, animals, and people, creating a sort
Speaker 1: of time stamp that's enabled researchers to measure when things
Speaker 1: have occurred, from the lifespan of white sharks to the
Speaker 1: growth of human knee cartilage and even brain cells. It's
Speaker 1: enabled forensic investigators to estimate the age and year of
Speaker 1: death for human remains with much greater precision than was
Speaker 1: previously possible. Okay, let's talk about how radiocarbon dating works,
Speaker 1: because using the bomb pulse to date living or previously
Speaker 1: living tissue is an advancement from the conventional radiocarbon dating
Speaker 1: that uses naturally occurring carbon fourteen before the article. This
Speaker 1: episode is based on How Stuff Works. Spoke via email
Speaker 1: with Thomas D. Holland, a research professor and the director
Speaker 1: of the Forensic Institute for Research and Education at Middle
Speaker 1: Tennessee State University. He explained radiocarbon dating has long been
Speaker 1: a mainstay of archaeologists. All living things absorb carbon during life.
Speaker 1: This includes the most common form of the atom carbon twelve,
Speaker 1: as well as the radioactive form carbon fourteen, and now
Speaker 1: these two isotopic forms exist in a known ratio which
Speaker 1: is reflected in the carbon in the tissues of living things.
Speaker 1: When an organism dies, it stops taking in carbon, and
Speaker 1: the atoms of carbon fourteen, which are unstable, will start
Speaker 1: to decay at a predictable rate. They have a half
Speaker 1: life of approximately fivey seven hundred years. A carbon twelve, meanwhile,
Speaker 1: is stable, so the more time that passes, the more
Speaker 1: the ratio of carbon fourteen to carbon twelve will decline.
Speaker 1: So by measuring that ratio you can put a fairly
Speaker 1: accurate date on when any given organism stop taking in carbon.
Speaker 1: The big limitation of radiocarbon dating has always been the
Speaker 1: error range. Holland said. Estimated dates derived from the radioactive
Speaker 1: decay of carbon fourteen have a plus minus error range
Speaker 1: based on the size and quality of the sample. Generally,
Speaker 1: error ranges for a good sample are no more than
Speaker 1: a few hundred years, which for most archaeological purposes is insignificant,
Speaker 1: a rendering carbon dating a valuable tool in the archaeological toolkit.
Speaker 1: This error range problem, however, it does present a real
Speaker 1: limitation when the material being dated may be less than
Speaker 1: one hundred years old. For example, human remains found buried
Speaker 1: somewhere or recovered from a lake. Holland said, a skeleton
Speaker 1: found buried in the woods may be a recent murder victim,
Speaker 1: or they may represent an early settler to the area.
Speaker 1: Traditional radiocarbon dating may allow for a point estimate of
Speaker 1: the person's year of death, but if it's accompanied by
Speaker 1: a plus minus error range of two hundred years, it
Speaker 1: renders the estimate of little use, at least in forensic contexts.
Speaker 1: But this is where the bomb pulse comes in. The
Speaker 1: amount of naturally occurring carbon fourteen in our atmosphere is
Speaker 1: relatively constant because it's created by cosmic radiations striking our
Speaker 1: atmosphere relatively constantly. The bomb pulse, though, is not constant.
Speaker 1: Holland said. In the thirteen years that above ground nuclear
Speaker 1: bomb tests were conducted, did the relative amount of carbon
Speaker 1: fourteen in the atmosphere almost doubled the normal level. Viewed
Speaker 1: on a longitudinal chart, the total amount of carbon fourteen
Speaker 1: present in the atmosphere shows a dramatic pulse in late
Speaker 1: nineteen sixty three, followed by a gradual decline of approximately
Speaker 1: four percent a year as the artificial bomb created carbon
Speaker 1: fourteen is absorbed out of the atmosphere by living things
Speaker 1: and the ocean. That means that if a skeleton found
Speaker 1: in the woods doesn't show the presence of large amounts
Speaker 1: of carbon fourteen, that's a pretty good indication that it
Speaker 1: dates from before nineteen fifty. But if there's evidence of
Speaker 1: the bomb pulse's effects, then the bones probably belong to
Speaker 1: a person who died sometime between nineteen fifty and the present.
Speaker 1: But wait, there's more, Holland said. Additionally, because the graph
Speaker 1: of atmosphere carbon fourteen shows a sharp upward slope beginning
Speaker 1: with the first nuclear bomb test in nineteen fifty, peaking
Speaker 1: in late nineteen sixty three when the test ban Treaty
Speaker 1: was signed, and then a more gradual absorption curve continuing
Speaker 1: into the present, it may be possible to fine tune
Speaker 1: the date of death for individuals who died post nineteen
Speaker 1: fifty By examining tissues with different growth and turnover rates,
Speaker 1: such as fingernails and hair relative to bone, Scientists can
Speaker 1: estimate where on the bomb pulse downward slope the sample
Speaker 1: falls and speculate a more exact age. Holland explained tissues
Speaker 1: that remodel slowly, such as bone, which may take years
Speaker 1: to turnover, will reflect the higher concentration of bomb carbon
Speaker 1: fourteen than will tissues such as hair, which will reflect
Speaker 1: carbon fourteen absorbed closer to the time of death and
Speaker 1: therefore lower on the declining slope. This can result in
Speaker 1: estimates of year of death within one to five years,
Speaker 1: and those estimates are pretty accurate. Study found that the
Speaker 1: carbon fourteen levels and fingernails can help scientists determine the
Speaker 1: year of death within ninety one percent accuracy, and the
Speaker 1: bomb pulse isn't just useful for dating human bodies. Researchers
Speaker 1: have also used the bomb pulse to study the ages
Speaker 1: of ivory seized from the ivory trade to determine whether
Speaker 1: it's antique or from recent poaching, and to measure the
Speaker 1: time period between when a coca leaf was harvested in
Speaker 1: South America and the cocaine made from it was seized
Speaker 1: in the United States. And oceanographers have used carbon to
Speaker 1: determine how the oceans are absorbing carbon dioxide. The main
Speaker 1: problem for scientists is that the bomb pulse will only
Speaker 1: be useful for tracking dates within a narrow time window.
Speaker 1: Holland said the bomb pulse will run its course by
Speaker 1: approximately twenty thirty and carbon fourteen levels will return to
Speaker 1: their pre nineteen fifty level, So we'll have to come
Speaker 1: up with other ways of more exact dating in the future.
Speaker 1: And on that note, I'll leave you with an old joke.
Speaker 1: If it weren't for carbon fourteen, I wouldn't date at all.
Speaker 1: Today's episode is based on the article the Surprising silver
Speaker 1: Lining of the Atomic Age nuclear tests on how stuffworks
Speaker 1: dot Com, written by Patrick J. Khider. Brain Stuff is
Speaker 1: production of iHeartRadio in partnership with HowStuffWorks dot Com and
Speaker 1: is produced by Tyler Klang. Four more podcasts my heart Radio,
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