Seventy-one years ago Saturday, a United States B-29 bomber named the “Enola Gay” dropped the atomic bomb “Little Boy” over the Japanese city of Hiroshima.
The bomb fell just over 29,000 feet from the plane and detonated 1,900 feet above Shima Hospital, an active medical center with a history dating back to the 18th Century. Between four and five square miles of buildings were leveled in the blast generated by just 141 pounds of highly enriched uranium. The US Department of Energy (DoE) estimates 70,000 people died in the initial blast, resulting fires, and radiation burst on August 6, 1945, but that the five-year death toll may have exceeded 200,000 people.
President Harry Truman told Japan to surrender or “expect a rain of ruin from the air, the like of which has never been seen on this earth.” Three days later, a second bomb (this time plutonium-based) dropped from an American warplane over the city of Nagasaki. The DoE estimates 40,000 people died in the immediate aftermath, and that number may have reached 140,000 within five years.
These events remain the only cases, so far, of human beings attacking other human beings with nuclear weapons. But the survivors of these attacks are from from the only people to carry the marks of nuclear warfare in their bodies.
Every person alive on the 71st anniversary of those attacks holds in their flesh radioactive remnants of the nuclear era — a period centered in the early decades of Cold War when nuclear nations conducted atmospheric tests of ever-larger bombs.
Hundreds of bombs detonated in the open air (and several more in the ocean) during the heyday of atmospheric nuclear testing — with thousands more tests conducted underground.
As Carrie Arnold reported in 2013 for Nova, the massive, unusual carbon-14 load of the era between 1955 and 1963 remains in the atmosphere. It’s called the “bomb pulse,” and it still makes its way, through plants, into the food web. But every second it decays a little more, leaving less in the atmosphere.
That means that every new cell created has a bit less carbon-14 than cells before it. And that slow decline proceeds in a predictable way.
In the last couple decades, researchers have taken advantage of that predictability to figure out exactly how old individual cells are. The process is fairly simple: Extract the cell’s DNA, measure its carbon-14 levels with a tool called a mass spectrometer, and check the result against tables of carbon-14 decay in the period since 1963.
This technique has been used, as Arnold reports, to trace the progress of cancers, advance our understanding of obesity and diabetes, and prove that brain cells continue to form through a human being’s lifetime.
However, barring a nuclear war or a rogue state conducting more dangerous above-ground tests, this method has a limited lifespan. Within a few decades, the bomb pulse will fade until it’s indistinguishable from our planet’s background carbon-14. (The researchers Arnold spoke to peg the date at 2050.)
Read more at Every baby born in 2016 contains atom bomb radiation — here’s why