Peiser studies known craters for clues to the past. But he also examines religions and cults, old and new, for signs of what might have happened way back then.

"I would not be surprised if the notorious rituals of human sacrifice were a direct consequence of attempts to overcome this trauma," he says of the South American impact craters. "Interestingly, the same deadly cults were also established in the Near East during the Bronze Age."

The impact of comets on myth and religion has reverberated through the ages, in Peiser's view.

"One has to take into consideration apocalyptic religions [of today] to understand the far-reaching consequences of historical impacts," he says. "After all, the apocalyptic fear of the end of the world is still very prevalent today and can often lead to fanaticism and extremism."

It is in the context of such apocalyptic religions that a large meteorite, enshrined in the Kaba in Mecca, became the most feared and venerated object of the Islamic faith, Peiser said.

By using such language, radical fundamentalist leaders instill "absolute commitment and fanaticism into their followers," Peiser said. "Once you believe that the end is imminent and that your direct action will hasten the coming of end-times, every atrocity is sanctioned."

Despite the excitement of the newfound hole in the ground in Iraq, it is still far from clear why so many civilizations collapsed in such a relatively short historical time frame. Few scientists, even those who find evidence to support the idea, are ready to categorically blame a comet.

French soil scientist Marie-Agnes Courty, who in 1997 found material that could only have come from a meteorite and dated it to the Early Bronze Age, urged caution on drawing any conclusions until a smoking gun has been positively identified.

"Certain scientists and the popular press do prefer the idea of linking natural catastrophes and societal collapse," Courty said.

Multiple cosmic impacts are an attractive culprit though, because of the many effects they can have, including some found in real climate and geologic data. The initial impact, if it is on land, vaporizes life for miles around. Earthquakes devastate an even wider area. A cloud of debris can block out the Sun and alter the climate. The extent and duration of the climate effects is not known for sure, because scientists have never witnessed such an event.

It might not have taken much. Ancient civilizations, which depended on farming and reliable rainfall, were precarious.

Mike Baillie, a professor of palaeoecology at Queens University in Belfast, figures it would have taken just a few bad years to destroy such a society.

Even a single comet impact large enough to have created the Iraqi crater, "would have caused a mini nuclear winter with failed harvests and famine, bringing down any agriculture based populations which can survive only as long as their stored food reserves," Baillie said. "So any environmental downturn lasting longer than about three years tends to bring down civilizations."

Other scientists doubt that a single impact would have altered the climate for so long.

Either way, there is a giant scar on the planet, near the cradle of civilization, that could soon begin to provide some solid answers, assuming geologists can get permission to enter Iraq and conduct a study.

"If the crater dated from the 3rd Millennium B.C., it would be almost impossible not to connect it directly with the demise of the Early Bronze Age civilizations in the Near East," said Peiser.

"Paradoxically, the Hebrew Bible and other Near Eastern documents have kept alive the memory of ancient catastrophes whose scientific analysis and understanding might now be vital for the protection of our own civilizations from future impacts," Peiser said.