Theories abound on how Earth got its water.
Most widely embraced is that asteroids, and maybe comets, crashed into our planet and released the water they held — in the form of ice or hydrated minerals in their crystal structures — and over time water became our oceans. The inflow was especially intense during what is called “the Late Heavy Bombardment,” some 4 billion years ago.
The isotopic composition of our water is comparable to water in asteroids in the outer asteroid belt, and so it makes sense that they could have delivered the water to Earth,
But there is also the view Earth formed with the components of water inside the planet and the H₂O was formed and came to the surface over time. Several hydrous minerals in our mantle store the necessary elements to create water and in this theory the pressure from hot magma rising up and cooler magma sinking down crushes this hydrous material and wrings them like a sponge. Water would then find its way to the surface through volcanoes and underwater vents.
Now a new model has been proposed and it has a novel interest because it originates in the discovery of thousands of exoplanets in the past quarter century.
This new approach, described by Anat Shahar of the Carnegie Institution for Science and colleagues from UCLA in the journal Nature, says that Earth’s water could have come from the interactions between of a very early and primarily hydrogen atmosphere and the scalding ocean of magma that covered the planet.
That the planet could have had a thick hydrogen atmosphere that wasn’t quickly destroyed is a new idea and it comes from the finding that many so-called “super-Earth” exoplanets have, or had, such an atmosphere. While super-Earths are larger and more massive than Earth, many are rocky, terrestrial planets and so share characteristics with our planet.
“Exoplanet discoveries have given us a much greater appreciation of how common it is for just-formed planets to be surrounded by atmospheres that are rich in molecular hydrogen, H2, during their first several million years of growth,” Shahar said.… Read more