© 2014 Peter Free
Citation — to study
Blair Schoene, Kyle M. Samperton, Michael P. Eddy, Gerta Keller, Thierry Adatte, Samuel A. Bowring, Syed F. R. Khadri, and Brian Gertsch, U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction, Science (via Science Express), DOI: 10.1126/science.aaa0118 (11 December 2014)
Citation — to press release
Morgan Kelly, New, tighter timeline confirms ancient volcanism aligned with dinosaurs’ extinction, Princeton University (18 December 2014)
In regard to the causes of the Cretaceous-Paleogene boundary extinction event:
The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs.
Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction.
Here we apply U-Pb [uranium-lead] zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million km3 of basalt erupted in ~750,000 years.
Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.
© 2014 Blair Schoene, Kyle M. Samperton, Michael P. Eddy, Gerta Keller, Thierry Adatte, Samuel A. Bowring, Syed F. R. Khadri, and Brian Gertsch, U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction, Science (via Science Express), DOI: 10.1126/science.aaa0118 (11 December 2014) (at Abstract) (paragraph split)
The interesting methodological twist
From the press release:
Schoene and his co-authors gauged the age of petrified lava flows known as basalt by comparing the existing ratio of uranium to lead given the known rate at which uranium decays over time.
The uranium and lead were found in tiny grains — less than a half-millimeter in size — of the mineral zircon. Zircon is widely considered Earth’s best “time capsule” because it contains a lot of uranium and no lead when it crystallizes, but it is scarce in basalts that cooled quickly.
The researchers took the unusual approach of looking for zircon in volcanic ash that had been trapped between lava flows, as well as within thick basalt flows where lava would have cooled more slowly.
© 2014 Morgan Kelly, New, tighter timeline confirms ancient volcanism aligned with dinosaurs’ extinction, Princeton University (18 December 2014) (paragraph split)
More to do, of course
Again, from Morgan Kelly:
Vincent Courtillot, a geophysicist . . . said that the paper is important and “provides a significant improvement on the absolute dating of the Deccan Traps.”
Courtillot, who is familiar with the Princeton work but had no role in it, led a team that reported in the Journal of Geophysical Research in 2009 that Deccan volcanism occurred in three phases, the second and largest of which coincides with the K-Pg mass extinction.
The Princeton researchers also plan to test the three-phases hypothesis, Schoene said. Their data already suggests that the second and third phase might be a single period of eruptions bridged by smaller, “pulse” eruptions, he said.
© 2014 Morgan Kelly, New, tighter timeline confirms ancient volcanism aligned with dinosaurs’ extinction, Princeton University (18 December 2014) (extracts)
Even with the apparent narrowing of the Deccan volcanism’s time relationship to the extinction window, 250,000 years before the boundary layer was presumably formed is a long time.
Yet, one member of the team makes a good dynamics-based counter-argument:
Existing models of the environmental effects of the Deccan eruptions used timelines two to three times longer than what the researchers found, which underestimated the eruptions’ ecological fallout, [Gerta] Keller explained.
The amount of carbon dioxide and sulfur dioxide the volcanoes poured out would have produced, respectively, a long-term warming and short-term cooling of the oceans and land, and resulted in highly acidic bodies of water, she said.
Because these gases dissipate somewhat quickly, however, a timeline of millions of years understates the volcanoes’ environmental repercussions, while a time frame of hundreds of thousands of years — particularly if the eruptions never truly stopped — provides a stronger correlation.
The new work confirms past work by placing the largest Deccan eruptions nearer the K-Pg extinction, but shows a much shorter time frame of just 250,000 years, Keller said.
“These results have significantly strengthened the case for volcanism as the primary cause for the mass extinction, as well as for the observed rapid climate changes and ocean acidification” . . . .
© 2014 Morgan Kelly, New, tighter timeline confirms ancient volcanism aligned with dinosaurs’ extinction, Princeton University (18 December 2014) (paragraphs split)
The moral? — Good thinking, increasing plausibility
However, given the huge chunks of time and what I assume is a somewhat impressionistically dated paleontological record, I am not yet convinced that we will be able to distribute persuasive degrees of extinction causation between Chicxulub and the Traps.