An asteroid impact on Mexico's Yucatan Peninsula is now widely believed to be the main event that sent the dinos to their doom. Now an impact crater in France is getting the honor of giving the “terrible lizards” their chance to take over the Triassic.
Paul Olsen and Dennis Kent of Columbia University's Lamont-Doherty Earth Observatory have been struck by the Triassic asteroid hypothesis for years, reported the journal Nature. But they didn't have proof. There was no smoking gun like the Chicxulub crater in the Yucatan.
What they were missing was evidence of what caused the wave of extinctions between the Triassic and Jurassic when, approximately 200 million years ago, many of the animals that shared the Earth with early dinosaurs disappeared within a few thousand years.
With mammal-like therapsids, crocodile-style archosaurs, and other beasts mostly out of the way, dinos rose to dominate life on Earth for the next 135 million years.
Earlier ideas about what may have caused this die-off related to the break-up of the super-continent Pangaea. Any heart-broken soul will tell you that a nasty break-up can feel like the end of the world, but the break-up of Pangaea puts that in perspective. Massive volcanoes spewed lava, ash and greenhouse gases as the continents tore apart.
Such a massive disruption may have been enough to cause extinctions, but the eruptions occurred over hundreds of thousands of years. The Triassic-Jurassic extinction took only a few thousand.
“The only thing anyone can say with any certainty about the Triassic–Jurassic mass extinction is that it happened,” Olsen told Nature. “Whatever it was that caused it, it happened so swiftly that most life forms never had time to adapt and evolve to meet the changes.”
But a possible clue lies in Europe.
An asteroid impact site near Rochechouart, France was re-dated last year to 199 million to 203 million years ago, perfect timing to coincide with the Triassic-Jurassic extinctions. Other evidence of an asteroid strike at the time of the extinction include a layer of grainy material in the geologic record oriented as if it came from the area of Rochechouart, Olsen told Nature.
Though the French crater is likely too small to have caused the extinctions by itself, it may have had accomplices. Other small asteroids could have struck at the same time. Or the impact may been the final straw that pushed a ecosystems already stressed by volcanic eruptions over the brink.
Read more at Discovery News
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