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It’s referred to as the “Great Dying” and it is the biggest mass extinction our planet has ever experienced.
What caused it? Geologists have identified the smoking gun: the Siberian Traps in Northern Siberia. Traps, the Swedish word for stairs, refers to the stepped appearance of lava flows that oozed from a vast rift in the Earth’s crust for nearly a million years. Flowing in fits and starts, like a chocolate fountain, it covered a region the size of Western Europe in lava one kilometre thick.
Our planet produces one of these monstrous “flood basalt” eruptions roughly every 30 million years. They occur, scientists believe, when portions of the ocean floor sink into Earth’s mantle, leaving magma nowhere to go but up. Compared with the brief, explosive volcanic eruptions we are familiar with today, flood basalts are in a class of their own.
The distribution of hotspots on the Earth has a distinct antipodal character, which has previously been shown to be statistically significant for one long (117) and two short ( ˜40-50) hotspot lists . One possible mechanism for the creation of antipodal hotspot pairs is the focusing of seismic energy from a major bolide impact at its antipode. Reflected tensile body waves would converge along the axis beneath the antipode possibly causing fracturing to depth , and the greatest focusing of seismic energy from fundamental-mode surface waves has been shown to occur in the antipodal asthenosphere where seismic attenuation is greatest . A major impact, therefore, might produce hotspot volcanism at the impact site (particularly on oceanic crust ), and produce flood basalts and a second hotspot from the focused disruption at its antipode.
Studies suggesting the permian extinction was quick
The new study is the latest in a series showing the Permian-Triassic catastrophe was quick at least in geological terms and extremely nasty.
But it has not settled debate among those who advocate various theories of what caused the extinction: an object whacking Earth, floods of lava from the Siberian Traps, climate change, and/or deadly radiation from a nearby supernova or other cosmic explosion.
In July, Doug Erwin of the Smithsonian Institutions National Museum of Natural History published a study in Science in which marine rocks from China revealed the Permian-Triassic extinction happened in less than 160,000 years.
And in Julys issue of the journal Geology, a study of seafloor rocks now in the Austrian Alps concluded the extinction happened in less than 60,000 years and perhaps in less than 8,000 years, said the main author, planetary scientist Michael Rampino of New York University.
Because the rock layers do not permit finer dissection of time, the findings are consistent with the extinction being triggered by an impact that happened during "a single bad day," Erwin said.
"The mass extinction at the end of the Permian Period was catastrophic and sudden," ravaging sea and land life, Rampino said. "The only thing we know of that can cause an extinction like this is a large impact of an asteroid or comet. But we still havent found conclusive evidence that an impact occurred."
Rampino said the object "would have to be bigger one and a half to twice as big" as the 6-mile- (10-kilometer-) wide asteroid usually blamed for the dinosaurs extinction.
In 1997, University of Oregon paleontologist Gregory Retallack reported finding elevated iridium levels and shocked quartz crystals in Permian-Triassic rocks telltale signs of an impact.
"Unfortunately, we have not found a good candidate crater," he said.
Ward said a comet made of ice "would be almost invisible geologically."
Last April, Australian scientists said they found a 75-mile- (120-kilometer-) wide crater in western Australia that might be from an impact that caused the Permian-Triassic extinction or a later extinction at the end of the Triassic Period roughly 200 million years ago.
But Rampino said the age of that crater is so poorly known that "it is impossible to tie that impact to this [Permian-Triassic] extinction."
Nevertheless, Retallack favors impact as the cause, perhaps with the impact triggering an undersea release of methane that robbed the oceans of life-sustaining oxygen. He says the impact also may have triggered massive eruptions from volcanic vents named the Siberian Traps.
The crater is about 300 miles wide. It was found by looking at differences in density that show up in gravity measurements taken with NASA's GRACE satellites. Researchers spotted a mass concentration, which they call a mascon-dense stuff that welled up from the mantle, likely in an impact.
"If I saw this same mascon signal on the Moon, I'd expect to see a crater around it," Frese said. (The Moon, with no atmosphere, retains a record of ancient impacts in the visible craters there.)
So Frese and colleagues overlaid data from airborne radar images that showed a 300-mile wide sub-surface, circular ridge. The mascon fit neatly inside the circle.
"And when we looked at the ice-probing airborne radar, there it was," he said today.
The Permian-Triassic extinction, as it is known, wiped out most life on land and in the oceans. Researchers have long suspected a space rock might have been involved. Some scientists have blamed volcanic activity or other culprits.
The die-off set up conditions that eventually allowed dinosaurs to rule the planet.
The newfound crater is more than twice the size of the Chicxulub crater in the Yucatan peninsula, which marks the impact that may have ultimately killed the dinosaurs 65 million years ago. The Chicxulub space rock is thought to have been 6 miles wide, while the Wilkes Land meteor could have been up to 30 miles wide, the researchers said.