Raw Story has a report on new research that suggests that the event that killed off the dinosaurs may have been more complicated than previously thought.
Until now, it has been accepted generally that the Chicxulub impact off the coast of Mexico 65 million years ago wiped out the dinosaurs. Evidence of the crater left by the giant asteroid or comet has been found under the sea off the coast of Yucatan.
But a group of scientists led by Professor Gerta Keller of Princeton and Professor Wolfgang Stinnesbeck of the University of Karlsruhe begged to differ. They uncovered a series of geological clues which suggests the truth may be far more complicated.
I’ve long thought it likely that the Alvarez’ theory regarding the Chixulub impact was only part of the story. I haven’t read the paper for this new research, so I can’t evaluate its accuracy beyond a very superficial level, but I suspect they’re on to something. Here’s the specific argument they seem to be making:
The previous impact theory was beautifully simple and appealing. Much of its evidence was drawn from a thin layer of rock known as the “KT boundary.” This layer is 65 million years old (which is around the time when the dinosaurs disappeared) and is found around the world exposed in cliffs and mines.
For supporters of the impact theory, the KT boundary layers contained two crucial clues. In 1979, scientists discovered that there were high concentrations of a rare element called iridium, which they thought could only have come from an asteroid. Right underneath the iridium was a layer of spherules, tiny balls of rock which seemed to have been condensed from rock which had been vapourised by a massive impact.
But Keller’s team concentrated on a series of rock formations in Mexico where the iridium layer was separated from the spherule layer by many metres of sandstone. Keller found evidence such as ancient worm burrows that suggested that the deposition of the sandstone had been interrupted many times.
Her team concluded that there was a gap of some 300,000 years between the deposition of the spherules (from the Chicxulub crater) and the iridium (from an asteroid). Therefore, there must have been two impacts.
Again, this seems quite reasonable to me without having seen the data. They speculate that a second, possibly larger impact occured in India. So far, they have not found the actual crater. It’s possible that this event may have triggered the astonishing series of volcanic eruptions that produced the Deccan basalts:
The Chicxulub impact conspired with the Deccan Flood Basalt eruptions in India, a period of prolonged and intense volcanic activity, to nudge species towards the brink, said Dr Keller.
Vast amounts of greenhouse gas were pumped into the atmosphere by the Deccan volcanism over a period of more than a million years. By the time Chicxulub struck, land temperatures were seven to eight degrees Celsius warmer than they had been 20,000 earlier.
Weakened by these events, species were finally killed off by the second impact.
I’d like to read the papers to see if the data supports this hypothesis at this point, but my initial reaction is that it seems a more likely scenario than the Alvarez hypothesis by itself.