It may not have been an asteroid after all. Massive Volcanic Eruptions Could Have Killed Off the Dinosaurs:
Physicist Luis Alvarez of the University of California, Berkeley, first presented the asteroid impact hypothesis in 1980. It was based on an extensive layer of iridium, which is associated with impacts, that could be found in many places across the globe in the same geologic time sequence. A decade later, the Chicxulub crater was discovered on the Yucatan peninsula, adding weight to the idea that an impact killed off the dinosaurs.The idea that Indian volcanoes, known as the Deccan Traps, might have contributed to the mass extinction is not new. But scientists at the AGU meeting think the eruptions could be the sole cause of the die-offs, and that the asteroid had little or no effect on life at all.
“If there had been no impact, we think there would have been a massive extinction anyway,” Courtillot said.
Courtillot has studied the magnetic signatures of the Indian volcanic deposits that lined up with the Earth’s magnetic field as they cooled. Because the orientation of the magnetic field has changed over time, lava that cooled at different times have different signatures.
The more than 2-mile thick pile of Deccan Traps deposits has several major pulses that occurred over the course of several decades each, almost certainly less than 100 years. And the entire sequence erupted in less than 10,000 years, rather than the million years or more that has been suggested.
All told, this would have put 10 times more climate-changing emissions into the atmosphere than the asteroid impact.
Also supporting the volcanic theory is fossil evidence from Texas and Mexico that most of the species extinctions coincided with the final pulse of eruptions, not with the asteroid impact, which may have occurred approximately 300,000 years earlier, according to Gerta Keller of Princeton University.
“There is essentially no extinction associated with the impact,” Keller said.
Evidence that dinosaurs survived in India right up to the final volcanic onslaught further bolsters the case.