The Earth has just given up a very alien secret: Scientists are reporting in Nature Communications that a rock found in a limestone quarry in Sweden is the first of its kind to have been discovered on our planet, a "biscuit-sized" remnant of a space rock they believe collided with another much larger one, reports AFP.

We have long uncovered evidence of that larger rock in the form of meteorites known as chondrites. Space.com explains that about 470 million years ago, L-type chondrites began to reach our surface 100 times more frequently than they previously had, indicating that their parent asteroid collided with another around that time.

The cosmic-ray exposure age—also 470 million years—of what's been dubbed Österplana 65 provides "very strong empirical evidence" that the new meteorite was part of that second body, says lead author Birger Schmitz.

Schmitz says Öst 65 may be the first ever "extinct" meteorite found on Earth in that it no longer falls because its parent body has been obliterated by collisions.

His 25-year search for meteorites from the Ordovician Period was getting "boring," he tells the BBC, as his team "found 50, then 60, then 70" L-type chondrites.

But in 2011 they uncovered Öst 65, which they referred to as "'the mysterious object' because it didn't resemble anything." After five years of analysis "we're certain of what it is." Interesting side note: The 3-inch rock was found in a quarry that produces floor tiles and "threw out" the ones that "had ugly black dots in them" That is, until the researchers asked it to stop.

"The very first fossil meteorite we found was in one of their dumps," says Schmitz. (Check out the legal battle over this 4.5-billion-year-old meteorite.)

This article originally appeared on Newser: A 'Biscuit-Sized' Rock May Clear Up a Space Mystery

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