Mere minutes after a miles-wide asteroid slammed into Earth 66 million years ago, a hailstorm of tiny glass beads rained down on a flooding estuary in what's now North Dakota. As seismic waves from the impact thrashed the water, plants and animals were jumbled up and buried in the shifting sediments, which preserved the aftermath for millennia.

Now, researchers say this site—newly described in a paper in the Proceedings of the National Academy of Sciences—represents an exceedingly rare snapshot of the moment that marked the dinosaurs' demise. Handfuls of fossils have been found before at other places that also capture this moment in the geologic record, known as the K-Pg boundary. But the North Dakota site potentially represents