What follows describes one of the most astonishing and sublime facts from science that I have learned in the last few years:
It is a little-known fact that the Cold War waged decades ago between the Soviet Union and the United States has fundamentally altered the physical composition of current human beings. Specifically, we have far more radioactive carbon in our bodies due to the nuclear test explosions than any humans that have ever lived.
The above-ground nuclear testing by the two superpowers between 1955 and 1963 nearly doubled the worldwide natural isotopic ratio of carbon-14 to carbon-12 (these atoms are more succinctly symbolized as 14C and 12C). 12C has 6 protons and 6 neutrons and constitutes 99% of the carbon found on earth, while the 14C isotope has two extra neutrons that render 14C atoms radioactive (isotopes are atoms of the same element that differ in their number of neutrons). While 14C constitutes a staggeringly miniscule amount of natural carbon (only about one atom in a trillion is 14C), its radioactivity is nevertheless the foundation for radiocarbon dating. A gram of natural carbon will undergo about 12 radioactive decays a minute, which can be detected by the beta radiation generated as the 14C turns into nitrogen, 14N.
Before humans decided to explode hundreds of nuclear weapons above ground in the early 1950’s, all living life forms had a rock-solid steady 14C/12C ratio that only varied by fractions of a percent over the millennia. The energy and temperature of the thermonuclear reactions generated significantly new amounts of 14C, however, which quickly combined with oxygen (O2) to make 14C-enriched carbon dioxide (CO2). All plants breath in CO2 the way animals breath oxygen, so shortly after the nuclear testing all plants began to have more 14C than they used to have, and everything that ate those plants, and everything that ate those things that ate those plants, all of a sudden had 14C-enriched bodies. That still includes you and me.
So, for over a hundred thousand years, humans had a constant 14C/12C in their body, but now in the last 50 years that ratio has been altered due to the Cold War nuclear arms race. Humans are more radioactive now that we used to be–literally.
It gets even more interesting, though. That excess 14C from the Cold War era is slowly being sequestered away from the natural above-ground carbon cycle as it is either absorbed into the oceans or ground. So, ever since the nuclear test ban treaty of 1963 essentially ended above-ground nuclear testing, the elevated 14C/12C isotopic ratio has been steadily reverting to the pre-1955 level. This is clearly evident by sampling tree rings, which provide a time capsule of yearly isotopic ratios (see figure above).
This natural, regular decline of the 14C/12C ratio since 1963 enabled scientists to determine for the first time ever the age of brain cells in humans.(!) By determining the 14C/12C isotopic ratio in brain cells of deceased subjects, and comparing that to the known yearly decline of the ratio since 1963, the year the brain cells were created can be determined. It was found for the first time that brain cells are not newly generated beyond childhood, at least not in a significant amount. Your brain cells that are created as a developing toddler are the brain cells you die with as an elderly adult. This is further verified by studying the isotopic ratio in blood cells, which are known to be regenerated anew in a matter of days. Every subject tested showed isotopic ratios of their blood corresponding to the atmospheric ratio of the year they died, whereas their brain cells showed the isotopic ratio from the years they were a toddler.
To summarize, then: thanks to excessive nuclear weapons testing prompted by the Cold War, you have more radioactive carbon in your body than pre-1955 humans and medical science was provided with a technique to date human cells and answer an important outstanding question in brain science. How old are brain cells? It turns out they are nearly as old as you are.