For the last few years, the reigning theory as to why the dinosaurs died out 65 million years ago has been asteroids, specifically the Baptisina family of asteroids. Now, thanks to new research from NASA, that theory has been toppled harder than the dinosaurs themselves.
The theory started back in 2007, when the Southwest Research Institute in Colorado—which had previously developed its own method to determine what collisions looked like in the young solar system—identified the Baptisina asteroids as the likely cause of the Cretaceous-Tertiary extinction event.
Specifically, one large asteroid, Baptisina, collided with another asteroid in the 160 million-year-old asteroid belt, sending fragments of the original hurtling toward those unsuspecting dinos.
But according to NASA, its NEOWISE (Wide-field Infrared Survey Explorer) mission discovered the Baptisina asteroids weren't formed 160 million years ago, as previously thought:
The NEOWISE team measured the reflectivity and the size of about 120,000 asteroids in the main belt, including 1,056 members of the Baptistina family. The scientists calculated the original parent Baptistina asteroid actually broke up closer to 80 million years ago, half as long as originally proposed.
The period between Baptisina's breakup and the extinction event is 15 million years. Although we consider that a long time, it's not long enough to be dinosaur-killing years. NASA scientists say that it takes tens of millions of years for asteroid remnants to "move into a resonance spot ... where gravity nudges from Jupiter and Saturn can act like a pinball machine to fling asteroids out of the main belt and into the region near Earth."
In other words, there wasn't enough time for the Baptisina asteroids to unseat dinosaurs as the champions of planet Earth and give our rat-sized forebears the chance to grow and develop brains, thumbs, upright spines and beer guts.
Of course we're still left with one important question: If the Baptisina asteroids didn't cause the extinction ... what did?