Silver Lining

Scientists are pretty sure by now that an asteroid or comet ended the 135 million-year reign of the dinosaurs. A huge chunk of space debris slammed into the earth 65 million years ago, blasting a pall of dust into the air. With the sun blocked, temperatures plunged and light-starved plants at the bottom of the food chain died. Bad news for the dinos, good news for the rodent-like beasts that suddenly had breathing room to begin evolving into us.

But new evidence from ancient lake beds in the Northeast U.S. suggests that the dinosaurs got their big break in just the same way our ancestors did. Scientists from Columbia University's Lamont-Doherty Earth Observatory and their colleagues have found iridium, a mineral plentiful in asteroids, in sediment about 200 million years old--just when the dinosaurs started to take over the planet. Fossilized footprints show that the dinosaurs evolved very rapidly at that time, from the size of dogs to that of dragons. And fossils of fern spores suggest that these opportunistic plants had a sudden ecological opening for colonization.

Is the evidence definitive? Not yet. But it does hint that nature has a powerful sense of poetic justice.

--By Michael D. Lemonick