Sixty years ago, scientists demonstrated that cosmic rays react with nitrogen (14N) in the atmosphere, substituting a neutron for a proton to produce 14C (Libby, 1946; Libby et al., 1949). Soon it was discovered that 14C is radioactive and that this isotope of carbon—better known as radiocarbon—would be useful as a clock for determining the age of materials on Earth (see Box 1). In particular, 14C dating of the organic remains of living organisms has been an indispensable tool for archaeologists, paleontologists, historians, and geochemists, whose work fundamentally depends on determining when in the past an organism or whole ecosystem was alive.

Ingalls, A.E., and A. Pearson. 2005. Ten years of compound-specific radiocarbon analysis. Oceanography 18(3):18–31, https://doi.org/10.5670/oceanog.2005.22.

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