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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00:03 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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