00:00 A Cretaceous scene of mass death in North Dakota shows that the asteroid that ended
00:12 the reign of the dinosaurs struck when it was springtime in the northern hemisphere.
00:17 The site is called Tanus, and abundant fish fossils reveal that a river once flowed there.
00:22 But 66 million years ago, just minutes after a massive asteroid crashed near the Gulf of
00:27 Mexico, a wave swept upstream and buried dozens of animals alive, turning the site into a
00:33 death pit.
00:36 Scientists recently analyzed fish fossils from Tanus, looking for clues about the impact.
00:41 They found tiny glass balls called spherules embedded in the fish's gills.
00:46 The spheres fused from ultra-hot sediments when the asteroid ejected towering plumes
00:50 of dirt from the impact crater.
00:53 Other researchers had previously calculated that impact spherules would have fallen from
00:57 the sky between 15 and 30 minutes after the asteroid crashed into Earth.
01:02 Because the spheres were in the fish's gills but hadn't been swallowed, the fish were likely
01:06 buried alive just after inhaling the glassy beads, within 30 minutes after the impact.
01:13 The scientists then used powerful X-ray scans to examine the fish's bones.
01:18 They mapped patterns and growth cycles over time, finding that bone growth peaked by the
01:22 end of the summer and then declined over the winter.
01:26 When the fish died, they were just entering a time of significant bone growth, which coincided
01:31 with spring.
01:35 Analysis of carbon isotopes in the bones revealed a similar pattern in the plankton that the
01:38 fish were eating.
01:40 Plankton are most numerous in summer.
01:42 Carbon traces in the fish bones showed that plankton numbers were growing, but hadn't
01:46 reached peak abundance yet.
01:48 This told the scientists that the fish died when it was still springtime.
01:53 TANIS offers a remarkable 3D snapshot of the immediate aftermath of the Earth-shaking asteroid
01:59 impact, and researchers suspect that there are other such sites that have yet to be discovered.
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