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(CNN)A tiny fragment of the asteroid that hit Earth 66 million years ago may have been found encased in amber -- a discovery NASA has described as "mind-blowing."
It's one of several astounding finds at a unique fossil site in the Hell Creek Formation in North Dakota that has preserved remnants of the cataclysmic moment that ended the dinosaur era -- a turning point in the history of the planet.
The fossils unearthed there include fish that sucked in debris blasted out during the strike, a turtle impaled with a stick and a leg that might have belonged to a dinosaur that witnessed the asteroid strike.
The story of the discoveries is revealed in a new documentary called "Dinosaur Apocalypse," which features naturalist Sir David Attenborough and paleontologist Robert DePalma and airs Wednesday on the PBS show "Nova."
Palaeontologist Robert DePalma is pictured at the Tanis dig site in North Dakota.
The ultimate bad day
DePalma, a postgraduate researcher at the University of Manchester in the United Kingdom and adjunct professor for the Florida Atlantic University's geosciences department, first started working at Tanis, as the fossil site is known, in 2012.
The dusty, exposed plains starkly contrast with what the site would have looked like at the end of the Cretaceous Period. Back then, the American Midwest was a swampy rainforest, and an inland sea that has since disappeared -- known as the Western Interior Seaway -- ran all the way from what's now the Gulf of Mexico to Canada.
Tanis is more than 2,000 miles away from the Chicxulub impact crater left by the asteroid that struck off the coast of Mexico, but initial discoveries made at the site convinced DePalma that it provides rare evidence of what led to the end of the dinosaur era.
The Tanis fossil site in North Dakota would have been a swampy rainforest 66 million years ago.
The site is home to thousands of well-preserved fish fossils that DePalma believed were buried alive by sediment displaced as a massive body of water unleashed by the asteroid strike moved up the interior seaway. Unlike tsunamis, which can take hours to reach land after an earthquake at sea, these moving water bodies, known as a seiche, surged out instantaneously after the massive asteroid crashed into the sea.
He's certain that the fish died within an hour of the asteroid strike, and not as a result of the massive wildfires or the nuclear winter that came in the days and months that followed. That's because "impact spherules" -- small bits of molten rock thrown up from the crater into space where they crystallized into a glass-like material -- were found lodged in the gills of the fish. Analysis of the fish fossils has also revealed the asteroid hit in spring.
"One piece of evidence after another started stacking up and changing the story. It was a progression of clues like a Sherlock Holmes investigation," DePalma said.
"It gives a moment by moment story of what happens right after impact and you end up getting such a rich resource for scientific investigation."