Word: asteroids
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When a scientific principle is common knowledge even in grammar school, you know it has long since crossed the line from theory to established fact. That's the case with dinosaur extinction. Some 65 million years ago - as we've all come to know - an asteroid struck the earth, sending up a cloud that blocked the sun and cooled the planet. That, in turn, wiped out the dinosaurs and made way for the rise of mammals. The suddenness with which so many species vanished after that time always suggested a single cataclysmic event, and the 1978 discovery...
...however, a study in the Journal of the Geological Society throws all that into question. The asteroid impact and dinosaur extinction, say the authors, may not have been simultaneous, instead occurring 300,000 years apart. That's an eyeblink in geologic time, but it's a relevant eyeblink all the same - one that occurred at just the right moment in ancient history to send the extinction theory entirely awry. (See pictures of meteors striking the earth...
...controversial paper was written by geoscientists Gerta Keller of Princeton University and Thierry Addate of the University of Lausanne, in Switzerland. Both researchers knew that challenging the impact doctrine would not be easy. The asteroid charged with killing the dinosaurs, after all, left more than the Chicxulub crater as its calling card. At the same 65-million-year depth, the geologic record reveals that a thin layer of iridium was deposited pretty much everywhere in the world. Iridium is an element that's rare on Earth but common in asteroids, and a fine global dusting of the stuff is precisely...
Keller's and Addate's species samplings are not, of course, conclusive, and plenty of other surveys since 1978 do tie the extinctions closely to the asteroid. But since the new digs were so close to ground zero, the immediate species loss ought to be have been - if anything - greater there than anywhere else in the world. Instead, the animals seemed to escape unharmed. Other paleontologists, however, believe that the very proximity of El Peñón to the impact site makes the results even less reliable. Earthquakes and tsunamis that resulted from the collision could have wrought havoc...
...Chicxulub asteroid didn't kill the dinosaurs, what did? Paleontologists have advanced all manner of other theories over the years, including the appearance of land bridges that allowed different species to migrate to different continents, bringing with them diseases to which native species hadn't developed immunity. Keller and Addate do not see any reason to stray so far from the prevailing model. Some kind of atmospheric haze might indeed have blocked the sun, making the planet too cold for the dinosaurs - it just didn't have to have come from an asteroid. Rather, they say, the source might have...