CHICAGO (CBS) — Later this year, the Field Museum of Natural History will begin displaying rare fossil meteorites that were embedded in a sea bed a half billion years ago.

They were found in a limestone quarry in Sweden in the 1950s. They sat in an office for three decades until an expert noticed them and determined they’re meteorites.

Now in the possession of the museum, they’ll go on display later this year.

Dr. Philipp Heck, a Field Museum meteorite expert and the Associate Curator of Meteoritics and Polar Studies, gave the media a sneak preview on Wednesday.

“What you see here are four fossil meteorites. Fossil meteorites are extremely rare. They were deposited a long time ago – in this case 500 million years ago – into a sea bed,” he said.

They remain embedded in rock taken from the limestone quarry. The rock was sliced into small slabs. Each is roughly the size of a golf ball. But to Dr. Heck they’re huge.

“You can call these the Mona Lisa’s of meteorites. There are only four but they’re extremely spectacular,” he said.

Of 50,000 meteorites known to science, Heck said only 1010 are fossil meteorites.

The slab of rock containing one of the meteorites also contains the fossil of a fish.

“It’s in the limestone, not in the meteorite. The meteorite didn’t kill that animal. They were just deposited at the same time,” Heck said.

Heck also held up a meteorite that fell in Park Forest in 2003. Testing has determined that meteorite broke off from the same from the same asteroid as the samples from Sweden. He said it floated around in space for a long time before entering Earth’s atmosphere.

“We have different lines of evidence that indicate that they all came from the same asteroid between Mars and Jupiter 500 million years ago, after this asteroid got disrupted by a major collision. That collision was the most violent collision that occurred in the Solar System in the last three billion years,” he said.

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