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Whenever we look for extraterrestrial life, we look for water—because we know that it's all thanks to water that life formed on Earth. So water is important for our continued existence, and this is a watery planet… but somehow, we're not entirely sure where that water came from. Astronomers have thought for years that Earth was dry in the beginning and it got its water most likely delivered on comets or asteroids from the outer solar system that pummeled.

Earth as it was forming. But a paper published last week in the journal Science suggests that Earth got at least some of its water much closer to home— and that it might have actually started out wet. The evidence comes from a type of meteorite called an enstatite chondrite or EC.

ECs originated in the inner solar system— they're basically the leftovers of the material that glommed together to form Earth. In the past, scientists have thought that objects that formed so close to the Sun wouldn't have been able to hold onto water, which would just vaporize in such high temperatures. But some models have suggested that these objects could have retained some water through adsorption, the process of physically or chemically locking water to a surface.

It turns out ECs actually have a lot more water than we'd assumed. The authors of the paper figured this out by measuring the amount of hydrogen in 13 ECs, assuming that all this hydrogen was either currently or previously part of a water molecule. It's not a perfect method, and hydrogen can take many other forms, but at least it provides an upper limit for how much water is locked up in the rock.

And it tells us that if Earth formed mostly out of ECs, the water inside these rocks could account for at least three times the amount of water currently on the Earth's surface. Which isn't out of the question:. Overall, the composition of these rocks is really similar to Earth's, so the authors believe it's likely that ECs were the main building blocks for Earth.

But… even if Earth formed with a lot of water, that doesn't necessarily mean it kept all the water it formed with. Remember, this was a really hot process, like, magma-ocean hot. So, the authors acknowledge that while Earth may have kept that initial water, it may have also lost a lot of it to evaporation.

But even if it did, ECs could still be our water source! Now that we know how much water there is in these rocks, we don't necessarily need comets and asteroids from the outer solar system to explain how all this water ended up here. At least some of that water could have come from nearby ECs, which were also colliding with Earth.

And not only does that tell us something about where our water comes from, it also tells us something about how watery planets can form in general! In other meteorite news, the authors of a study published last week in the journal Science Advances took a look at the special kinds of minerals that form during meteorite impacts. These events produce such high temperature and pressure that they rearrange the molecules in minerals to form new crystal structures called polymorphs.

These days, the only other place on Earth with conditions like these is deep in the mantle, and we can't drill down that far. So impact sites are a good way to get an idea of what Earth's interior is like without actually going there. Scientists are especially interested in what happens to quartz in these conditions.

Quartz is important because it's one of the main components of Earth's crust, and it gets recycled over time as tectonic activity churns things up. But we don't actually know what exactly happens to material from the crust as it gets pulled into the depths of the Earth. We can get an idea, though, by looking at what happens to quartz at impact sites.

In the early 1960s, scientists started doing research at a crater in Arizona and found a polymorph called stishovite. Like quartz, it had an ordered, crystal lattice structure made up of silica, a combination of silicon and oxygen atoms. As a result, scientists assumed that the stishovite was once quartz that had been transformed in the impact.

But the authors of last week's study realized that was a mistake:. They'd been trying to figure out how quartz transforms into stishovite by giving it a shock of high temperature and pressure in the lab. Except, instead of getting stishovite, they produced a totally new polymorph!

Unlike both quartz and stishovite, which have a nice crystalline structure, its molecules were mostly disordered. It was also not very stable. It would revert back to a mix of crystalline quartz and glassy silica after a little bit of time—which explains why no one has found this polymorph in any impact craters.

But what it doesn't explain is where stishovite comes from, since that definitely has been found in impact craters. The key is that silica can take many different forms in nature. It can have ordered crystal structure, like both quartz and stishovite, or it can have no structure at all, like opal and glass.

And researchers found that stishovite just comes from a different form of silica instead of quartz: It comes from glass! Even though this study didn't turn out as expected, all of these findings help us better model what's going on inside the Earth, and how rocks composed of crystals react to the conditions in the mantle. And that's important—because not only is this happening deep within Earth today, when Earth was young, transformations like these were happening all the time.

So, like the search for the origin of Earth's water, the study of impact craters can help us understand Earth's earliest days. Thanks for watching this episode of SciShow Space News, which was sponsored in part by. HBOmax's Raised by Wolves, now streaming.

These days, we're always learning something new about the other worlds out there, and sometimes, you can't help but wonder about what life would be like on a different planet. If you've ever thought about that, you might like this new sci-fi series Raised by Wolves from Ridley Scott, the director of The Martian. It explores a world where Earth has been destroyed and it's up to two androids to raise children on a mysterious, uninhabited planet.

As the new colony of humans starts breaking apart over religious differences, the androids learn how difficult and dangerous it is to try to control the beliefs of humans. If you're interested, you can click the link in the description to stream it now! {♫Outro♫}.