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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00:00A Cretaceous scene of mass death in North Dakota shows that the asteroid that ended
00:12the reign of the dinosaurs struck when it was springtime in the Northern Hemisphere.
00:17The site is called Tannus, and abundant fish fossils reveal that a river once flowed there.
00:23But 66 million years ago, just minutes after a massive asteroid crashed near the Gulf of
00:27Mexico, a wave swept upstream and buried dozens of animals alive, turning the site into a
00:33death pit.
00:36Scientists recently analyzed fish fossils from Tannus, looking for clues about the impact.
00:41They found tiny glass balls called spherules embedded in the fish's gills.
00:46The spheres fused from ultra-hot sediments when the asteroid ejected towering plumes
00:50of dirt from the impact crater.
00:53Other researchers had previously calculated that impact spherules would have fallen from
00:57the sky between 15 and 30 minutes after the asteroid crashed into Earth.
01:02Because the spheres were in the fish's gills, but hadn't been swallowed, the fish were likely
01:07buried alive just after inhaling the glassy beads, within 30 minutes after the impact.
01:13The scientists then used powerful x-ray scans to examine the fish's bones.
01:18They mapped patterns and growth cycles over time, finding that bone growth peaked by the
01:23end of the summer, and then declined over the winter.
01:26When the fish died, they were just entering a time of significant bone growth, which coincided
01:31with spring.
01:35Analysis of carbon isotopes in the bones revealed a similar pattern in the plankton that the
01:39fish were eating.
01:40Plankton are most numerous in summer.
01:43Carbon traces in the fish bones showed that plankton numbers were growing, but hadn't
01:47reached peak abundance yet.
01:49This told the scientists that the fish died when it was still springtime.
01:54TANIS offers a remarkable 3D snapshot of the immediate aftermath of the Earth-shaking
01:58asteroid impact, and researchers suspect that there are other such sites that have yet to
02:04be discovered.