Ancient Sudbury meteorite blasted debris into Michigan

A mountain-sized meteorite appears to have created Sudbury's gigantic crater and sent a tsunami racing though ancient oceans, say scientists who have uncovered a thick layer of debris the extraterrestrial interloper hurled all the way into Michigan.

A Canadian-U.S. team says the two-to-four-metre-thick layer of "ejecta," which they found south of Lake Superior, bears the clear signature of a meteorite.

Perhaps even more intriguing, they say the "ejecta" appears to have been stirred up by a "mega-tsunami," possibly two, that swept through the ancient oceans after the space rock hit.

"The material blown out of the crater was reworked during deposition by a tsunami," says Peir Pufahl, lead author of a report on the find in the September editions of the journal Geology. He says shock waves generated by the impact of the meteorite, believed to have been about the size of Mt. Everest, would have been powerful enough to generate giant waves in near-by oceans.

"We also get beautiful rock preserved in tear drops just as you'd expect if you had molten rock flying through the atmosphere and it cooled," Pufahl said in a interview.

The Sudbury crater, the second largest ever found, was formed 1.85 billion years ago and is much bigger than the one linked to the demise of the dinosaurs.

Some have suggested a comet carved out the crater, which originally measured up to 280 kilometres in diameter. But the material uncovered in northern Michigan points to a meteorite, since it contains an unusually high concentration of iridium, which occurs in low amounts in icy comets but in high levels in space rocks.

The "ejecta layer," which the geologists found buried a kilometre underground south of Lake Superior, builds on similar evidence uncovered near Thunder Bay, Ont., a few years ago. The newly found material not only contains high levels of iridium and "melt drops" but also "shocked" crystals deformed by the intense energy, and evidence of reworking by a tsunami, the team reports.



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The impact of the meteorite would have been felt globally but most of the evidence has eroded away over time. "It's like a book with 90 per cent of pages missing," says Pufahl.

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He says the huge cloud of gas and molten rock hurled into the atmosphere would have put photosynthesis on hold for an extended period and may be linked to a "long lull" in the evolution of early life.

Computer models have estimated the space rock could have been close to 20 kilometres across and travelling 20 kilometres a second, or 1,200 kilometres a minute, when it slammed into Earth.



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"That energy has to go somewhere," says Pufahl. "Some of it goes into deforming the rock it slams into, some of it obliterates the rock it slams into and throws it in to the atmosphere, and some of it is transmitted away from the impact as shock waves. It is those shocks waves that would impact on water to cause tsunamis."