North Dakota Fossil Site Reveals When Asteroid Killed Dinosaurs

A Cretaceous scene of mass death in North Dakota shows that the asteroid that ended the reign of the dinosaurs struck when it was springtime in the Northern Hemisphere. The site is called tennis, and abundant fish fossils reveal that a river once flowed there. But 66,000,000 years ago, just minutes after a massive asteroid crashed near the Gulf of Mexico, a wave swept upstream and buried dozens of animals alive, turning the site into a death pit. Scientists recently analyzed fish fossils from tennis, looking for clues about the impact. They found tiny glass balls called sparrows embedded in the fish's gills. The sphere is fused from ultra hot sediments when the asteroid ejected towering plumes of dirt from the impact crater. Other researchers had previously calculated that impacts ferals would have fallen from the sky between 15 and 30 minutes after the asteroid crashed into Earth. Because the spheres were in the fish's gills but hadn't been swallowed, the fish were likely buried alive just after inhaling the glassy beads within 30 minutes after the impact. The scientists then used powerful X-ray scans to examine the fish's bones. They mapped patterns and growth cycles over time, finding that bone growth peaked by the end of the summer. And then declined over the winter. When the fish died, they were just entering a time of significant bone growth which coincided with spring. Analysis of carbon isotopes in the bones revealed a similar pattern in the plankton that the fish were eating. Plankton are most numerous in summer. Carbon traces in the fish bones showed that plankton numbers were growing but hadn't reached peak abundance yet. This told the scientists that the fish died when it was still springtime. Tennis offers a remarkable 3D snapshot of the immediate aftermath of the Earth shaking asteroid impact. And researchers suspect that there are other such sites that have yet to be discovered.