We've all heard the expression, "Every cloud has a silver lining." Well, what about mushroom clouds?
With credit to Science's David Grimm for the pun, there is a silver lining here as well. The more than 500 atomic bombs detonated above ground from 1951 to 1963 led to a chemical "labeling" of our ecosystem, which is now being used by scientists to answer key questions in developmental biology. The most recent use of the technique was to determine if heart cells are capable regenerating themselves during one's lifetime.
Here's the history: the atomic bomb detonations resulted in a doubling of normal levels of atmospheric radioactive carbon. The isotope, known as carbon-14, or 14C, spread quickly throughout the plant and animal world. Plants took up 14C in the form of carbon dioxide, animals ate plants, humans ate animals, and in very short time all of the living world contained minuscule but significantly higher-than-normal quantities of 14C (one atom per 10-20 cells).
Since above-ground atomic bomb tests ended in 1963, the amount of 14C in the atmosphere has been falling (apparently mopped up by the oceans). It is predicted to return to pre-bomb levels in ~ 2020.
It turns out the sudden rise in 14C, followed by a steady decline, allows researchers to identify the historic age of a given cell population or tissue by measuring the sample's 14C content and comparing it to historic levels. Tooth enamel, for example, does not change much over one's lifetime. So by measuring the 14C in your tooth enamel today, this can be matched to historic atmospheric 14C levels, revealing your age +/- 1.5 years. Tissues that turnover rapidly, like skin, will have lower 14C levels because the DNA in the cells is new, built from carbon taken from an atmosphere lower in 14C. This figure in the NYT article helps explain it.
Just this week, this technique was used to show that human heart cells renew themselves at a rate of 1% per year in young adults, but that the regeneration rate slows by half as one approaches the age of 75. This finding strengthens hope that key organs in the body could theoretically be coaxed to repair themselves. All we need to do now is understand the underlying biology.
The clock is ticking, as they say, because these measurements will get more difficult as we get closer to "baseline" atmospheric levels of 14C in 2020.