DENVER--Most scientists believe that a meteor or comet wiped out the dinosaurs 65 million years ago. Now, Gregory Retallack, a geologist from the University of Oregon, Eugene, claims to have found evidence that another cosmic interloper may have paved the way for the dinosaurs' rise on Earth.
Some 250 million years ago, something wiped out trilobites and most other creatures, creating the conditions that gave rise to an explosion of new life forms, including the dinosaurs. Researchers have long speculated that either a huge impact or volcanic eruptions may have triggered a catastrophic climate change, which in turn caused this dramatic shift in the fossil record--a transition that marks the boundary between the Permian and the Triassic periods. But there's been little hard evidence to back up these theories.
Retallack, however, believes he has found the smoking gun: microscopic quartz crystals from rock layers dated to the late Permian. At the Geological Society of America meeting here, Retallack showed photos of the quartz, unearthed in Australia and Antarctica, in which he claims the crystals were fractured by an impact of cosmic proportions. Such a collision could have thrown dust into the atmosphere, triggered acid rain, or otherwise altered the climate such that nearly all life at the time went extinct, Retallack says.
Many scientists are skeptical of Retallack's claim but anxious to analyze his samples more closely. The photos are "intriguing but not convincing," says Philippe Claeys of Berlin's Museum of Natural History. "Making such claims about very old rocks is difficult," he says. What's needed now, he says, is a finer analysis of the crystals, perhaps by transmission electron microscopy.