No, dark matter probably did not do in the dinosaurs.

Resurfacing briefly in the midst of proposal writing, I feel compelled to comment on recent media coverage of Lisa Randall's new book.  The science story is an interesting one, as recounted here.   In brief:  There is some evidence of periodicity in mass extinctions due to impacts, though there are at least three hidden assumptions even in that statement.  One possible source of periodicity could be associated with the motion of the solar system (and by extension the earth) in and out of the galactic plane as the sun orbits the center of mass of the Milky Way.  Lisa Randall and Matthew Reece argued that passage through a comparatively thin disk of dark matter on the galactic plane could lead to gravitational perturbations that could lead to Oort Cloud comets getting dinked toward the inner solar system.  A neat idea, though pretty hard to test except through indirect means.  

So, could this have happened?  Sure.  Is it likely?  Well, that's much trickier to evaluate.  There are plenty of other sources of gravitational perturbations (e.g., the passage of nearby stars) that we know for sure take place.  There is no strong observational evidence right now that the would-be disk of dark matter exists, let alone whether it has the properties needed to provide a significant uptick in cometary impacts.  Lisa Randall is undoubtedly a gifted writer, and there is real science here (witness the published paper that discusses ways to test the idea), but the breathless media reaction is somewhat disappointing.