Smoking didn't kill the dinosaurs, but noxious gases may still share the blame. A new analysis of one of the Earth's largest existing lava flows lends support to a controversial theory that the dinosaurs were wiped out by volcano-induced climate change rather than a meteor impact.
The Mesozoic Era came to a sudden halt 65 million years ago with global mass extinctions on land and in the oceans. Scientists have long wrangled over the cause of the extinctions, focusing largely on two geological events that happened around the same time: the impact of a large meteorite at Chicxulub in Mexico's Yucatan peninsula, and the massive lava flows that resulted in a one and a half mile-thick layer of basalt known as the Deccan Traps of India. The Deccan theory suggests that the volcanic eruptions would have induced devastating climate changes by injecting vast amounts of dust and greenhouse gases, such as carbon dioxide and sulfur dioxide, into the atmosphere. However, one of its primary criticisms is that the Deccan eruptions are thought to have been spread out over a period of 500,000 to one million years, giving the climate plenty of time to adjust.
But new measurements of the magnetic alignments of minerals in the Deccan lava suggest that the eruptions may have occurred over a much shorter period of time, says Anne-Lise Chenet, a doctoral student in geophysics at the Laboratoire de Paleomagnetisme et de Geomagnetisme in Paris. Chenet, working with geophysicist Vincent Courtillot, observed strong correlations between the alignments of the minerals in the upper 600 meters of the Deccan Traps, suggesting those younger eruptions occurred over just 30,000 years. And although her analysis of the rest of the Deccan lava flows is not yet complete, Chenet says the older eruptions may have occurred even more rapidly. That's because, unlike the upper layers of the Deccan Traps, the lower layers don't show geological signs of weathering between successive lava flows. Chenet reports her findings today at the Earth Systems Processes 2 meeting in Calgary, Canada.
Such rapid eruptions wouldn't have given the climate time to recover, says Frederick Fluteau, a climatologist working with the team. However, proponents of the Chicxulub impact theory see many weak points in the story. "We don't know enough about the behavior and variability of the Earth's magnetic field" to make strong arguments based on magnetic alignment data, says Jan Smits of Vrije Universiteit in Amsterdam. He also questions whether any known geophysical mechanism could have spewed out so much lava in such a short time.
The Great Chicxulub Debate