Source Pravda.Ru

Crater reveals new evidence of the Great Dying

Researchers said they have found evidence of a meteor collision off the coast of Australia that may have caused the largest mass extinction in earth’s history – an event 251 million years ago known as the Great Dying.

Much like the meteor crater associated with the later extinction of dinosaurs, scientists say they have found signs of a 120-mile-diameter crater that could be linked to the Great Dying, which killed 90 percent of marine species and 70 percent of land species in a geological instant.

The announcement yesterday in the online version of the journal Science is reigniting a heated debate among researchers over what caused a series of major extinctions— and how likely such events are to happen again. While some scientists believe that these die-offs occur relatively abruptly, after catastrophic events such as meteor collisions, others believe they take much longer and are a result of far more gradual events, such as climate change, volcanism, or shifts in ocean chemistry, reports boston.com

According to sciam.com Luann Becker of the University of California at Santa Barbara and her colleagues studied two cores drilled by oil companies in the 1970s and 1980s into a geologic structure off the Australian coast known as the Bedout High. "The moment we saw the cores we thought it looked like an impact breccia," said Becker. Specifically, the team found what they say is evidence of a telltale melt layer that formed when a meteor crashed into the earth and created the 125-mile-wide Bedout. Additional support for their contention that Bedout is an impact crater comes from the fact that material from the cores dates to 250 million years ago, give or take 4.5 million years.

Together with earlier evidence that Becker and her team collected in Antarctica and Australia--including shocked quartz and molecules called fullerenes containing extraterrestrial helium and argon--the new results provide further evidence that a massive impact brought about the Great Dying, the scientists say. "We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," Becker remarks. "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."

Erwin acknowledged that the Becker team had provided additional evidence of an extraterrestrial impact, but "perhaps not yet compelling -- what's going to happen is that geologists and paleontologists will investigate this far more thoroughly and find more evidence to support or refute this interpretation."

He said the key task is to resolve the apparent conflict between the impact theory and the view that Siberian flood basalts caused the extinction. Scientists must make further efforts to accurately date both events to determine whether they are truly contemporaneous, he said.

If they are, he added, scientists must then determine whether the impact might somehow have caused the Siberian volcanism, inform washingtonpost.com