Larry O'Hanlon, Discovery News
A new statistical study of mass extinctions throughout the history of life on Earth is backing up the idea that no single meteor, volcanic eruption or other lone gunman is ever to blame, even in the case of the Cretaceous-Tertiary event that brought the end of dinosaurs 65 million years ago.
Instead, the worst die-offs happen when some sort of interminable, multi-generational pressure on life is combined with a few powerful blows. It's what is now being called the press/pulse theory of mass extinctions.
Reading the Cretaceous-Tertiary extinction literature conversations with colleagues "made me wonder whether the simplistic scenario of 'Everything's fine until one day in June when the asteroid hits and everything goes to hell-in-a-hand-basket' really explains the diversity of data," said plant fossil expert Nan Arens of Hobart and
Wouldn't it make more sense, she surmised, if certain species were already vulnerable when the triggering event happened?
To test the idea, she and then-undergraduate student Ian West compiled a large database of marine organisms and their extinctions through geological time.
They divvied up the last 488 million years into four groups: Suspected meteor impacts (pulses), gigantic volcanic flood basalt eruptions (presses), periods with neither presses nor pulses, and times when press and pulse coincided. They compared average extinction rates in each of these groups.
Flood basalt eruptions are considered "presses" because they release vast amounts of greenhouse gases into the atmosphere and can change the Earth's climate.
The researchers found similar extinction rates when a pulse or press occurred by itself, and when neither effect was occurring, said Arens. "However, when an impact occurred during a time of volcanic flood — that produced higher extinction rates."
Arens is presenting her work on Oct. 25 at the annual meeting of the Geological Society of America in
"The goal of our work was to come up with a unifying theory of mass extinctions," said West. They also wanted to make the theory applicable to the rapid extinctions now being seen as a result of accelerating climate change (press) and the ongoing destruction of wild habitats by human activities worldwide (pulse).
The theory "is essentially a more eloquent way of saying what I and many other paleontologists have been saying for many years," said Gerta Keller of
In the late Cretaceous case massive volcanism — the Deccan Traps eruption in
"I'm very happy they have done the analysis based on the literature and come up with the same conclusions that paleontologists have been preaching all along," Keller said.
