Earth may have been born wet
Earth may not have needed asteroid and comet strikes to fill its oceans. Conventional wisdom has long held that our planet was born dry, because its building blocks formed relatively close to the hot, baking Sun. Earth therefore got the vast majority of its water later, most scientists believe, from impacting objects native to the cold and icy depths of the outer Solar System.
Researchers have been arguing for years about whether comets or asteroids were the primary water bearers. Researchers analysed 13 different enstatite chondrite meteorites, a class known to be similar to the space rocks that coalesced to form Earth. They found lots of hydrogen in the supposedly dry meteorites – enough to imply that our planet was born quite wet. The calculations suggest that the rocks that formed Earth harboured at least three times as much water as the planet’s present-day oceans hold.
“Our discovery shows that Earth’s building blocks might have significantly contributed to Earth’s water,” said Laurette Piani, a researcher at the Centre de Recherches Pétrographiques et Géochimiques in France. “Hydrogen-bearing material was present in the inner Solar System at the time of rocky planet formation, even though the temperatures were too high for water to condense.”
Big questions remain about the timing of Earth’s water uptake, so it’s unclear if most of the water sloshing in our seas does indeed go all the way back. For example, if most of Earth’s native water was incorporated very early on, it may have been boiled away by long-ago asteroid bombardments and/or the formation of magma oceans. “The research brings a crucial and elegant element to this puzzle,” said Anne Peslier of NASA. “Earth’s water may simply have come from the nebular material from which the planet accreted.”