There is a buzz going around the blogosphere in the wake of press releases on a new paper coming out which challenges the asteroid impact correlation with the K-T extinction event.
This seems like an opportunity to point out that the whole search for a "smoking gun" in extinction events is probably off-target: All the largest extinction events in earth's history seem to be a result of positive interference between multiple factors which change the habitability of one or more environments on earth. In the case of the K-T event, the longer-term carbon cycle perturbation associated with the flood basalt eruption of the Deccan Traps in central India (68-60Ma) coincided with the Chixulub impact in Yucatan, Mexico (64.5Ma) as well as the increasing domination of the plant world by angiosperms (flowering plants) which may have been less edible to the terrestrial herbavores. Several other events, both fast and slow, have been suggested to correlate temporally with the end-Cretaceous extinctions.
WHY DO WE NEED A SMOKING GUN? Clearly this is a multiple-whammy event. Every K-T paper seems to have to take a side. From my reading it appears to me that a long (multiple-million-years) decline in biodiversity (caused by plate tectonics and climate effects such as volcanism and plate reorganization in latitude and coast-line length) was punctuated and probably accentuated by spikes in volcanism rates (CO2 increases) and at least one big asteroid impact. Without the combined effects of ALL of these driving factors, the extinction event would have been less pronounced, or the biota would have had more leeway to recover. Maybe the "everybody's right" approach isn't as headline grabbing.
Anyway, the more interesting discussion growing out of all this is the topic of scientific mavericy: the role of a scientist or group of scientists who argue against the generally preferred interpretations.
The Lab Lemming and my perennial favorite, Female Science Professor have each written superior posts on the topic. FSP in particular highlights the intrinsic value of minority opinions to the overall debate, while acknowledging the erroneous effects of the popular media's tendancy to highlight "both sides" of a "debate" by digging out a quote from some dinosaur who thinks the world is flat.
There are ways for non-experts, including science journalists to tell the difference! And we ought to hold them accountable for this!
The paper which triggered these discussions (Press Release here) reports some new stratigraphic work in the Yucatan area which IS INCONSISTENT with one of the key attributes of the hypothesis that the Chixulub Impact ALONE was responsible for the mass extinctions of the K-T boundary. The stratigraphy records both the extinction event and the impact event and they are NOT PRESENT IN THE SAME STRATIGRAPHIC LEVEL, suggesting that they did not occur at the same time.
This is a key piece of data, which is important to the ongoing conversation on the relative role of different factors which caused the extinction. The community of scientists who promote the idea that this impact directly led to the extinctions will have to somehow explain or discredit this data or their case for their model will be weakened. Although there will be moments of drama (and for us, a "dramatic moment" involves somebody standing up in a dark conference room and telling somebody else they are wrong.... ooooo drama), people are right now in their offices reviewing their own data sets and hypothesizing new explanations or new narratives that incorporate the new data along with all the existing data. Science will go on. So will the debates about the dinosaurs' extinction.
This does not make the authors of this study some kind of gadfly harbingers of doom, shooting poison darts into the currently dominant hypothesis. I beg of you, journalists and general public -- do not mistake the give-and-take of ideas, data and hypotheses in the scientific sphere for intellectual cage wrestling. Disagreeing does not have to lead to drama between scientists... it's part of our daily lives and we enjoy the process of working out the details to find concensus or narrow the points of contention. If you are married to or dating a scientist, you may experience the great joy of this process as an integral part of your personal life.