Comets and asteroids are responsible for several “mass extinctions” on Earth over the last 260 million years. Unless they’re not. That’s the somewhat muddled state of research into extinction events, in which much of the life on Earth dies off in a fairly short period. The most famous of these events took place about 65 million years ago. It killed the dinosaurs and other life. The leading idea says it was the result of a collision with a giant asteroid. A competing idea says it was caused by massive volcanic eruptions. But a recent study says it likely was both, with the asteroid impact amplifying the volcanic eruptions. Another study found that an extinction event more than 250 million years ago was more complicated than thought. It lasted a couple of million years, with life on land dying out long before life in the oceans. And it began well before a series of volcanic eruptions in Siberia, leaving no clear cause for the die-offs. But another study says there’s little doubt that mos
