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The Chilling Regularity of Mass Extinctions


One thing we know for sure is thatconditions on Earth were, shall we say, unpleasant for the dinosaurs at themoment of their demise. Alternate and overlapping theories suggest the greatbeasts were pelted with monster comets, drowned by mega-tsunamis, scorched withlava, starved by a landscape stripped of vegetation, blasted with the radiationof a dying supernova, cloaked in decades of darkness, and frozen in an ice age.


Renne is the author of another new studythat focuses on the Chicxulub crater, the massive divot beneath the YucatánPeninsula that was created by the same impact blamed for the extinction of thedinosaurs. Renne and his colleagues believe that the comet or asteroid thatblasted into Earth and made Chicxulub also set off a global chain-reaction ofvolcanic eruptions that accelerated the end of the dinosaurs. Volcanoes were,they believe, erupting continuously for millions of years. Long enough to makeHawaii’s Kilauea, which has been flowing since 1983, seem laughable. (“Kilaueais nothing,” Renne told me. “Kilauea is a flea.”)


And while Renne is interested in thepossibility that volcanism is tied to intervals of mass extinction, thatpossible connection doesn’t explain what kind of cycles might trigger the awakeningof Earth’s most powerful magma systems on a global scale. That’s wheretheories about galactic periodicity come back into play.


“[Muller] doesn’t even believe that anymore,” Renne told me.


If Rampino and Caldeira are correct, thenext mass extinction may not be far off—in geologic terms, anyway. Our littlecorner of the solar system crossed the plane about 2 million years ago, and weare now moving up and through it. “In the Galactic theory, we are near theGalactic plane, and we have been in the danger zone for a couple of millionyears,” Rampino said. “We are still close to the plane, maybe 30 light yearsabove the plane, [and] a light year is 6 trillion miles … We won’t come backacross the plane for about another 30 million years.”


In the meantime, scientists are activelyscouring the skies, and calculating the orbits of monstrous comets andasteroids. “So far, none are on a collision course, but the work has just begunin earnest,” Rampino said. “Once we know one is coming, then there are severaloptions to divert the object. (You don’t want to blow it up, that will justincrease the numbers of impactors.) One possibility is to have a nuclearexplosion off to one side of the comet or asteroid, pushing it just slightlyoff course, or possibly just hitting the object with a rapidly movingspace-craft would provide enough of a nudge.”