In a new study published Thursday in the journal Science, researchers pieced together the chemical identity of the asteroid that fueled the planet’s fifth mass extinction event. Sixty-six million years ago, the story of life on Earth took a dramatic turn when an asteroid collided with what’s now the Yucatán Peninsula in Chicxulub, Mexico. The aftereffects of the collision resulted in the extinction of an estimated 75% of animal species, including most dinosaurs except for birds. But practically nothing of the asteroid itself remains. In a new study published Thursday in the journal Science, researchers pieced together the chemical identity...