Deuterium levels in mantle argue against comets as H2O source
Magnús Tumi Guðmundsson
Molecules entombed inside pristine magmas suggest that Earth’s water came from soggy dust, not icy comets.
The relative abundance of a heavier variety of hydrogen called deuterium serves as a fingerprint of where in the solar system a reservoir of H2O originated (SN: 5/16/15, p. 18). Previous work hunting for the source of Earth’s water measured deuterium in seawater, but that’s a tainted metric, researchers report in the Nov. 13 Science. Aboveground processes such as hydrogen atoms leaking into space can hike deuterium concentrations in the planet’s surface water (SN: 9/5/15, p. 8).
The researchers found that deuterium levels in water trapped inside molten rock unaltered since the planet’s early days are