The moon is far more than a largely dead orb. Our planet’s pale satellite is the creator of tides, the catcher of meteors and the only other world in the starry ocean where humanity has set foot. But scientists are still not entirely clear how it was made. Solving this mystery would not only reveal the moon’s origins, it would also help explain our own planet’s evolution.

A study published on Monday in Nature Geoscience suggests that the moon was forged from the fires of an ocean of magma sloshing over baby Earth’s surface. If correct, this model may solve a longstanding paradox.

Lunar meteorites and samples collected during the Apollo missions show that the moon and Earth have remarkably similar geochemical fingerprints. Scientists suspect that this was likely the result of a giant impactor the size of Mars, known as Theia, that slammed into a young Earth and sent into orbit a spiral of material that coalesced into the moon.

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Countless computer simulations show that this is possible, but there’s a problem. Such an impact on a relatively solid Earth would have created a moon made mostly out of Theia, not Earth (at least in simulations resulting in the Earth-moon system we observe today, complete with our 24-hour days).