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00:03 A Cretaceous scene of mass death in North Dakota
00:10 shows that the asteroid that ended
00:12 the reign of the dinosaurs struck
00:14 when it was springtime in the northern hemisphere.
00:17 The site is called Tanis, and abundant fish fossils
00:20 reveal that a river once flowed there.
00:23 But 66 million years ago, just minutes
00:25 after a massive asteroid crashed near the Gulf of Mexico,
00:28 a wave swept upstream and buried dozens of animals alive,
00:32 turning the site into a death pit.
00:36 Scientists recently analyzed fish fossils from Tanis,
00:39 looking for clues about the impact.
00:41 They found tiny glass balls called spherules
00:44 embedded in the fish's gills.
00:46 The spheres fused from ultra-hot sediments
00:48 when the asteroid ejected towering plumes of dirt
00:51 from the impact crater.
00:53 Other researchers had previously calculated
00:55 that impact spherules would have fallen
00:57 from the sky between 15 and 30 minutes
01:00 after the asteroid crashed into Earth.
01:02 Because the spheres were in the fish's gills
01:04 but hadn't been swallowed, the fish
01:06 were likely buried alive just after inhaling
01:09 the glassy beads, within 30 minutes after the impact.
01:13 The scientists then used powerful X-ray scans
01:16 to examine the fish's bones.
01:18 They mapped patterns and growth cycles over time,
01:21 finding that bone growth peaked by the end of the summer
01:24 and then declined over the winter.
01:26 When the fish died, they were just
01:28 entering a time of significant bone growth, which
01:30 coincided with spring.
01:32 Analysis of carbon isotopes in the bones
01:36 revealed a similar pattern in the plankton
01:38 that the fish were eating.
01:40 Plankton are most numerous in summer.
01:42 Carbon traces in the fish bones showed
01:44 that plankton numbers were growing,
01:46 but hadn't reached peak abundance yet.
01:48 This told the scientists that the fish died
01:51 when it was still springtime.
01:53 TANIS offers a remarkable 3D snapshot
01:56 of the immediate aftermath of the Earth-shaking asteroid
01:59 impact, and researchers suspect that there
02:02 are other such sites that have yet to be discovered.
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