Water has made the Earth the planet that it is—a planet known for its blue oceans. Water shapes the land through erosion and is fundamental to Earth’s ability to support life. But we have a hard time understanding exactly how Earth ended up with all this water, as the building blocks that created it were likely to be dry, and the collisions that turned these building blocks into a planet should have driven any surface waters off into space.

Various means have been proposed to deliver water to Earth after its formation. But a new study takes information we’ve gained from examining exoplanets and applies this to Earth. The results suggest that chemical reactions that would have occurred during Earth’s formation would have produced enough water to fill the world’s oceans. And, as a side benefit, the model explains the somewhat odd density of the Earth’s core.

Waterproof

The Earth seems to have primarily been constructed from materials in the inner Solar System. Not only were those materials in the right place, but present material found in asteroids of the region provided good matches in terms of their elemental and isotopic composition. But these materials are also very dry. That’s not a surprise; the temperatures in this area would have kept water from condensing out as a solid, as it can further out in the Solar System, beyond a point known as water’s “ice line.”