Did Water Crash Into Earth From Space?

Did water crash into Earth from space by way of a massive comet, or was it around long before our planet’s formation? Well, one new study suggests that it might have actually come from the most unlikely source of all: the Sun.

Between oceans, glaciers, polar ice caps, and lakes, watery goodness covers almost 71% of Earth’s surface. And that’s pretty special — Earth is the only one of the rocky planets in our solar system with this much water. So when it comes to BIG questions, one of the biggest is where did Earth’s water originally come from? One new study says maybe…the Sun? But to get there, we gotta start a little further back. For decades, planetary scientists and astrobiologists have been building two competing hypotheses for just how Earth got so gosh dang WET.

Option one: Water was inside the Earth when it formed in the first place. The idea goes that minerals in the mantle of our ancient, primordial Earth stored hydrogen and oxygen. When those minerals melted in the natural course of geothermal activity, the hydrogen and oxygen dissolved together in the magma as water. When that magma got spewed out onto Earth’s surface via volcanoes, the water came too. Alternatively, maybe those elements stored in Earth’s minerals were vaporized by an impact from some comet or asteroid… possibly even the BIG impact we think created our moon! Those vaporized elements combined and settled on the Earth’s surface, resulting in our life-giving liquid.

But option two is an answer that doesn’t come from so close to home. Many scientists think that water was just chillin’ on comets, meteorites, asteroids, etc out in space. When these guys crashed into us…hey presto, water on Earth! Where this gets a little sticky though, is the numbers. Scientists have studied the remnants of asteroids and meteorites that crashed into us wayyyyy back at our planet’s beginning. These do contain certain kinds of hydrogen, what are called isotopes. But the ratio of the hydrogen isotopes on these ancient astrophysical bodies doesn’t match the ratio in our oceans today. To get the right ratio, the water from these crashed objects would have needed to mix with another, lighter isotope of hydrogen for us to get the kind of water we have today.

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