How Did Hazardous Nuclear Testing Help Science?

Aboveground nuclear weapons testing in the 1950s and '60s has exposed every living thing on Earth to harmful radiation -- but has also made dating the remains of living things much more accurate. Learn more in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/nuclear-tests-bomb-pulse.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey, brain Stuff,
Lauren Vogel. Bomb here as wild as it seems to
us today. There was a time when the United States,
the Soviet Union, and other countries tested nuclear weapons by
exploding them right in Earth's atmosphere. From nineteen forty five

(00:23):
to nineteen sixty three, when such tests were finally banned
by an international treaty, more than five hundred nuclear bombs
were detonated, releasing radioactive fallout that spread far and wide
across the planet, causing harm to the environment and human health.
For example, everyone who's lived in the US after nineteen
fifty one has been exposed to nuclear fallout, and for

(00:47):
some it's resulted in an increased risk of thyroid cancer
according to the CDC. But for scientists, that fallout has
also provided an important measuring tool. The test caused a
spike in the atmospheric concentration of carbon fourteen, which is
an isotope or form of carbon that's radioactive but also

(01:09):
occurs naturally, just not usually in such a blump sum.
The excess carbon fourteen was distributed throughout Earth's atmosphere, peaking
in nineteen sixty three when the test ban went into effect.
This spike is called the carbon fourteen bomb pulse. That radioactivity,
which has gradually been declining since the nineteen sixties, has

(01:32):
been absorbed by plants, animals, and people, creating a sort
of time stamp that's enabled researchers to measure when things
have occurred, from the lifespan of white sharks to the
growth of human knee cartilage and even brain cells. It's
enabled forensic investigators to estimate the age and year of
death for human remains with much greater precision than was

(01:56):
previously possible. Okay, let's talk about how radiocarbon dating works,
because using the bomb pulse to date living or previously
living tissue is an advancement from the conventional radiocarbon dating
that uses naturally occurring carbon fourteen before the article. This

(02:17):
episode is based on How Stuff Works. Spoke via email
with Thomas D. Holland, a research professor and the director
of the Forensic Institute for Research and Education at Middle
Tennessee State University. He explained radiocarbon dating has long been
a mainstay of archaeologists. All living things absorb carbon during life.

(02:37):
This includes the most common form of the atom carbon twelve,
as well as the radioactive form carbon fourteen, and now
these two isotopic forms exist in a known ratio which
is reflected in the carbon in the tissues of living things.
When an organism dies, it stops taking in carbon, and

(02:58):
the atoms of carbon fourteen, which are unstable, will start
to decay at a predictable rate. They have a half
life of approximately fivey seven hundred years. A carbon twelve, meanwhile,
is stable, so the more time that passes, the more
the ratio of carbon fourteen to carbon twelve will decline.
So by measuring that ratio you can put a fairly

(03:20):
accurate date on when any given organism stop taking in carbon.
The big limitation of radiocarbon dating has always been the
error range. Holland said. Estimated dates derived from the radioactive
decay of carbon fourteen have a plus minus error range
based on the size and quality of the sample. Generally,

(03:43):
error ranges for a good sample are no more than
a few hundred years, which for most archaeological purposes is insignificant,
a rendering carbon dating a valuable tool in the archaeological toolkit.
This error range problem, however, it does present a real
limitation when the material being dated may be less than

(04:04):
one hundred years old. For example, human remains found buried
somewhere or recovered from a lake. Holland said, a skeleton
found buried in the woods may be a recent murder victim,
or they may represent an early settler to the area.
Traditional radiocarbon dating may allow for a point estimate of
the person's year of death, but if it's accompanied by

(04:27):
a plus minus error range of two hundred years, it
renders the estimate of little use, at least in forensic contexts.
But this is where the bomb pulse comes in. The
amount of naturally occurring carbon fourteen in our atmosphere is
relatively constant because it's created by cosmic radiations striking our

(04:48):
atmosphere relatively constantly. The bomb pulse, though, is not constant.
Holland said. In the thirteen years that above ground nuclear
bomb tests were conducted, did the relative amount of carbon
fourteen in the atmosphere almost doubled the normal level. Viewed
on a longitudinal chart, the total amount of carbon fourteen

(05:09):
present in the atmosphere shows a dramatic pulse in late
nineteen sixty three, followed by a gradual decline of approximately
four percent a year as the artificial bomb created carbon
fourteen is absorbed out of the atmosphere by living things
and the ocean. That means that if a skeleton found

(05:29):
in the woods doesn't show the presence of large amounts
of carbon fourteen, that's a pretty good indication that it
dates from before nineteen fifty. But if there's evidence of
the bomb pulse's effects, then the bones probably belong to
a person who died sometime between nineteen fifty and the present.
But wait, there's more, Holland said. Additionally, because the graph

(05:52):
of atmosphere carbon fourteen shows a sharp upward slope beginning
with the first nuclear bomb test in nineteen fifty, peaking
in late nineteen sixty three when the test ban Treaty
was signed, and then a more gradual absorption curve continuing
into the present, it may be possible to fine tune
the date of death for individuals who died post nineteen

(06:12):
fifty By examining tissues with different growth and turnover rates,
such as fingernails and hair relative to bone, Scientists can
estimate where on the bomb pulse downward slope the sample
falls and speculate a more exact age. Holland explained tissues

(06:33):
that remodel slowly, such as bone, which may take years
to turnover, will reflect the higher concentration of bomb carbon
fourteen than will tissues such as hair, which will reflect
carbon fourteen absorbed closer to the time of death and
therefore lower on the declining slope. This can result in
estimates of year of death within one to five years,

(06:56):
and those estimates are pretty accurate. Study found that the
carbon fourteen levels and fingernails can help scientists determine the
year of death within ninety one percent accuracy, and the
bomb pulse isn't just useful for dating human bodies. Researchers
have also used the bomb pulse to study the ages

(07:16):
of ivory seized from the ivory trade to determine whether
it's antique or from recent poaching, and to measure the
time period between when a coca leaf was harvested in
South America and the cocaine made from it was seized
in the United States. And oceanographers have used carbon to
determine how the oceans are absorbing carbon dioxide. The main

(07:39):
problem for scientists is that the bomb pulse will only
be useful for tracking dates within a narrow time window.
Holland said the bomb pulse will run its course by
approximately twenty thirty and carbon fourteen levels will return to
their pre nineteen fifty level, So we'll have to come
up with other ways of more exact dating in the future.

(08:02):
And on that note, I'll leave you with an old joke.
If it weren't for carbon fourteen, I wouldn't date at all.
Today's episode is based on the article the Surprising silver
Lining of the Atomic Age nuclear tests on how stuffworks
dot Com, written by Patrick J. Khider. Brain Stuff is

(08:23):
production of iHeartRadio in partnership with HowStuffWorks dot Com and
is produced by Tyler Klang. Four more podcasts my heart Radio,
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