Some of Earth’s water might have been here from the start

Nature : The origin of Earth’s water is an open question. Two possible sources are icy comets and asteroids that impacted the planet early in its history. Based on their analysis of ancient volcanic rock, Lydia Hallis, formerly of the University of Hawaii in Honolulu, and her colleagues are now arguing that some of the water was already here at the start of the solar system’s formation. When lava hardens quickly, it can form crystallized bubbles called melt inclusions that trap water and other compounds from the deep mantle, an area that still contains the primordial material that formed the planet. Hallis’s team vaporized those bubbles and analyzed the released material with a mass spectrometer. They looked at the ratio of two hydrogen isotopes, which can point to the origin of the water. The ratio of ordinary hydrogen to deuterium they found was similar to the ratio found in some classes of meteorites, but the ratio was lower than that in Earth’s oceans. However, the researchers believe that additional deuterium was collected as the material rose through the mantle. Based on that, they calculated that roughly 20% of the water in the samples was primordial.