Known as radiocarbon dating, this method provides objective age estimates for carbon-based objects that originated from living organisms.
The “radiocarbon revolution” made possible by Libby’s discovery greatly benefitted the fields of archaeology and geology by allowing practitioners to develop more precise historical chronologies across geography and cultures.
Organisms at the base of the food chain that photosynthesize – for example, plants and algae – use the carbon in Earth’s atmosphere.
They have the same ratio of carbon-14 to carbon-12 as the atmosphere, and this same ratio is then carried up the food chain all the way to apex predators, like sharks.
Libby cleverly realized that carbon-14 in the atmosphere would find its way into living matter, which would thus be tagged with the radioactive isotope.
Spalding and her postdoc advisor Jonas Frisén had a hunch that a pulse of radioactive carbon created by above-ground nuclear tests during the Cold War could help solve the riddle.
“A geopolitical phenomenon—this Cold War bomb testing—has, in a way, put a date stamp on everything and everybody,” Spalding says.
Other cells, like those in the adult brain and nervous system, have been viewed as more like the Mona Lisa. Spalding, once a postdoc at the Karolinska Institute in Stockholm, Sweden and now a professor there, knew there were tantalizing hints that the adult hippocampus—a seahorse-shaped region deep in the brain that is important for memory and learning—could regenerate neurons.
But without knowing exactly when each neuron was created, scientists couldn’t say with any certainty that this was true.