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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."
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 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."
Many of the latest discoveries revealed in the documentary haven't been been published in scientific journals.
Michael Benton, a professor of vertebrate paleontology at the University of Bristol, who acted as a scientific adviser on the documentary, said while it was a "matter of convention" that new scientific claims should go through peer review before being revealed on television, he and many other paleontologists accepted that the fossil site really does represent the dinosaurs' "last day."
"Some experts have said 'well, it might be the day after or a month before ... but I prefer the simplest explanation, which is that it really does document the day the asteroid hit in Mexico," he said via email.
Most of the glassy impact spherules that first revealed the fingerprints of the asteroid impact to DePalma are preserved as clay as a result of geological processes over millions of years. However, DePalma and his collaborators have also found some spherules that landed in tree resin on the surface of a log that fateful day and were preserved in amber.
"In that amber we've located a number of spherules that were basically frozen in time, because, just like an insect in amber which is perfectly preserved, when these spherules entered the amber, water couldn't get to them. They never turned to clay, and they're perfectly preserved," he said.
It's "like getting a sample vial, running back in time and getting a sample from the impact site and then saving it for science," DePalma said.
They were able to locate a number of little unmelted fragments of rock inside the glass spherules. Most of these tiny rock fragments were calcium-rich -- likely from the limestone under the Yucatan Peninsula, DePalma said.