Sixty-six million years ago, when a large asteroid struck what is now Mexico’s Yucatan Peninsula, the world’s forests were devastated by fire and ash—and the era of modern birds began. It was the end of the Cretaceous, though the dinosaurs—T. rex, Triceratops, Velociraptor, and bird-like Ichthyornis and Confuciusornis—that ruled Earth wouldn’t have known that. The climate was warm and humid, the poles had no ice sheets, sea level was hundreds of feet higher than today, and an ocean filled what is now central North America. Then, the asteroid struck, forming a crater 93 miles wide and 12 miles deep. The impact itself generated shockwaves emanating out in a 930-mile radius from the site, says Daniel Field, a paleobiologist at the Milner Center for Evolution at the University of Bath. “Trees would have been flattened from the force.” Catastrophic earthquakes and volcanic eruptions were triggered by the shockwaves, and widespread fires likely accompanied the impact...