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In a week in which crude oil reached its highest price since 1990, scientists have announced that the search for oil has led to the identification of a 250-million-year-old impact crater that may be associated with the worst mass extinction in history.
Other researchers are not convinced.
The Great Dying, as it is known, is firmly established in the fossil record. It wiped out nearly 90 percent of species in the ocean and more than two-thirds of vertebrate species on land, or more by some accounts. The cause has not been pinned down. Scientists have speculated a comet or asteroid may have been involved, and volcanism and climate change have also been blamed.
Researchers involved in the new study say multiple extreme situations, including an impact, probably combined to bring biology to its knees.
Drilling down
The team, led by geologist Luann Becker of the University of California, Santa Barbara examined undersea drilling samples taken by oil prospectors in the 1970s and '80s and since held in an Australian lab. They also studied ancient layers of Earth now exposed on land Down Under and in Antarctica.
Dated to the time of the mass extinction, they found breccia, a porous rock often linked to impacts. And they uncovered tiny glass beads and material known as shocked quartz, which has been fractured in several directions. These can be indicators of the extreme heat generated when a large, high-speed extraterrestrial object slams into the planet.
"Few earthly circumstances have the power to disfigure quartz, even high temperatures and pressures deep inside the Earth's crust," Becker said.
The findings point to the existence of a 125-mile-wide (200-kilometer) crater called Bedout off the northwest coast of Australia. The ring-like structure had previously been identified as a possible impact crater by seismic data and a map of gravity variations in the area.
Not so fast
The study is published today in the online version of the journal Science. Other experts in impact signatures are not sold.
There is "no convincing evidence for an impact origin" in the rocks that were studied, says Bevan French of the National Museum of Natural History in Washington, D.C. "Everything theyre arguing was shocked [by impact] can have nonshock origins." Volcanic activity is one possibility, according to a separate article also published in the online journal.
Impact geologist Richard Grieve of the Canadian Geological Survey in Ottawa has seen the results and is doubtful, too.
"I could be wrong, but I wouldnt add [Bedout] to the list" of proven impact craters, Grieve told the journal.
Oil traps
Speculation over the otherworldly origins of the Bedout structure goes back several years. In looking for sites to drill for oil, Australian geoscientist John Gorter suggested in 1996 that Bedout might have resulted from an asteroid or comet collision roughly 250 million years ago.
Though oil is commonly thought to have formed by the decay of dead organisms, some scientists think its origins are nonbiological. The main components of oil, hydrocarbons, were likely abundant deep inside the early Earth and, theorists say, could seep into the surface crust through cracks and fissures over time.
Asteroids and comets, which collided with Earth frequently in the distant past, delivered more hydrocarbons to the crust. Further, the breccia material common at impact sites is porous and holds oil well, so the basins of ancient craters are thought by some experts to be excellent oil traps.
In the jittery world oil market, the price rose above $40 a barrel Tuesday for the first time since a brief spike in 1990. Terrorist attacks on oil facilities and "voracious demand" for oil in the United States and China were cited by The New York Times as the main reasons for the hike.
In an interesting convergence of industry and science, other potential space rock scars could be uncovered if oil prices continue to rise.
Geologist Richard Donofrio calculated in the late 1990s that there are perhaps 20 large and unknown impact craters beneath the United States containing 50 billion barrels of untapped oil.
Additional investigations would please scientists, who say more crater sites and core samples are needed to sharpen knowledge of what's left behind by giant space rocks.
Multiple culprits?
A study in 2001 by Becker and others provided more clues that the Great Dying, which ended the Permian era and ushered in the Triassic, was caused at least in part by a collision. In that work, the researchers found extraterrestrial fullerenes, or "bucky balls" containing a type of helium in concentrations suggesting an object several miles wide had hit Earth around 250 million years ago. Other labs could not confirm the results, however.
Scientists wonder whether impacts might cause severe climate change or trigger extreme volcanism, or if they just happen to sometimes coincide in history, or if any one of the three catastrophes might alone lead to a die-off.
At the time of the Great Dying, Earth contained just one landmass, a giant region called Pangea. Geologic records from the time are difficult to trace because Pangea ultimately broke apart and spread into the present day continents, and material was often folded back into the planet.
But the effect of the upheaval is clear.
Rise and fall of dinosaurs
The Permian mass extinction studied by Becker's team altered the mix of species on Earth and paved the way for the emergence of dinosaurs. Another possibly asteroid-related extinction about 200 million years ago allowed dinosaurs to totally take over, another study showed.
A more recent impact, 65 million years ago, is thought to have contributed to the demise of dinosaurs. The hit left a clear calling card: the Chicxulub crater off Mexico's Yucatan Penninsula. (The event is now thought to be the possible source of Mexico's oil deposits).
Researchers once figured the Chicxulub impact was the primary cause of dinosaur death. But some scientists now think multiple catastrophes may have conspired for this extinction, too.
Becker is one of them.
"We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," Becker said. "This is what happened 65 million years ago at Chicxulub but was largely dismissed by scientists as merely a coincidence. With the discovery of Bedout I don't think we can call such catastrophes occurring together a coincidence anymore."
The study was funded by NASA and the National Science Foundation. Portions of the research by Becker's team, which includes geochemist Robert Poreda of the University of Rochester, have been published previously in other journals.
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