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 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 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 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 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 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
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.
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 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 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, 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 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 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 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 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 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 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 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 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, 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 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 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. 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 production of iHeartRadio in partnership with HowStuffWorks dot Com and is produced by Tyler Klang. Four more podcasts my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.