Results: Researchers from MIT and their collaborators have done the most detailed analysis ever of a layer of sediments deposited during and immediately after the asteroid impact 65 million years ago that wiped out the dinosaurs and 80 percent of Earth's marine life. They found that at least some forms of microscopic marine life — the so-called "primary producers," or photosynthetic organisms such as algae and cyanobacteria in the ocean — had recovered within about a century after the mass extinction.
Why it matters: Previous research had indicated the process might have taken millions of years. The new findings also support some theoretical analyses of the effects of the impact, which suggested that the atmosphere would have recovered from the obscuring blanket of impact dust relatively quickly, says MIT Professor of Geobiology Roger Summons. "The atmosphere must have cleared up rapidly," he says. "People will have to rethink the recovery of the ecosystems. It can't be just the lack of food supply" that made it take so long to recover. Finally, the new research seems to rule out one theory about how the global ecosystem responded to the impact, which held that for more than a million years there was a "Strangelove ocean" in which all the primary producers remained absent for a prolonged period, he says.
How they did it: The team had two major advantages that helped to make the new findings possible. One was a section of the well-known cliff face at Stevns Klint, Denmark, that happens to have an unusually thick layer of sediment from the period of the mass extinction — about 40 centimeters thick, compared to a few cm. thickness of the layer that Alvarez originally studied from that period, at Gubbio, Italy and at Stevns Klint. And they had the use of one of the most powerful Gas Chromatograph-Mass Spectrometers (GC-MS) in the world, a device that can measure minute quantities of different molecules in the rock. MIT's advanced GC-MS is one of only a few such powerful instruments currently available in U.S. universities.
Next steps: The team hopes to be able to study other locations with relatively thick deposits from the extinction aftermath, to determine whether the quick recovery really was a widespread phenomenon after the mass extinction.
Source: "Rapid resurgence of marine productivity after the Cretaceous-Paleogene mass extinction," by Julio Sepulveda et al, Science, Oct. 2, 2009
Funding: The work was funded by the DFG, European Graduate College Europrox and the NASA Astrobiology and Exobiology Programs.
Journal
Science