3. Climbing to the Top of Mount Fuji: Uniting Theory and Observations of Oxygen Triple Isotope Systematics

The near-simultaneous discovery of both minor isotopes of oxygen in 1929 was a watershed
moment for modern science, to say nothing of its impacts on isotope geochemistry. At the time,
oxygen was the international standard for atomic weight, as it had been for over twenty-five
years. However, chemists and physicists had grown fond of different definitions: physicists used
the weight of the 16O atom, while chemists used half the weight of atmospheric oxygen (O2) to
define the precise weight of 16 atomic mass units. While they usually avoided direct conflicts,
these contrasting definitions found an unexpected impasse in the near-infrared absorption
spectrum of atmospheric oxygen: it contained a series of faint lines that could not be explained
by any known atmospheric constituents.