North Dakota Fossil Site Reveals When Asteroid Killed Dinosaurs
Spring is a time for budding flowers, tender green leaves and baby animals. But 66 million years ago, that gentle season instead brought mass death and carnage from Earth's catastrophic impact with a massive space rock. Scientists recently pinpointed the season of the disaster and linked it to springtime in the Northern Hemisphere, after analyzing fossilized animals that died minutes after the impact at a site called Tanis, where a river once flowed through what is now North Dakota.
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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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