If you are fortunate enough to see the storm of shooting stars predicted for the Nov. 18 peak of the Leonid meteor shower, you'll be watching a similar but considerably less powerful version of events which some scientists say brought down the world's first civilizations.

The root of both: debris from a disintegrating comet.

Increasingly, some scientists suspect comets and their associated meteor storms were the cause. History and culture provide clues: Icons and myths surrounding the alleged cataclysms persist in cults and religions today and even fuel terrorism.

And a newly found 2-mile-wide crater in Iraq, spotted serendipitously in a perusal of satellite images, could provide a smoking gun. The crater's discovery, which was announced in a recent issue of the journal Meteoritics & Planetary Science, is a preliminary finding. Scientists stress that a ground expedition is needed to determine if the landform was actually carved out by an impact.

Yet the crater has already added another chapter to an intriguing overall story that is, at best, loosely bound. Many of the pages are washed away or buried. But several plot lines converge in conspicuous ways.

Archeological findings show that in the space of a few centuries, many of the first sophisticated civilizations disappeared. The Old Kingdom in Egypt fell into ruin. The Akkadian culture of Iraq, thought to be the world's first empire, collapsed. The settlements of ancient Israel, gone. Mesopotamia, Earth's original breadbasket, dust.

Around the same time -- a period called the Early Bronze Age -- apocalyptic writings appeared, fueling religious beliefs that persist today.

The Epic of Gilgamesh describes the fire, brimstone and flood of possibly mythical events. Omens predicting the Akkadian collapse preserve a record that "many stars were falling from the sky." The "Curse of Akkad," dated to about 2200 B.C., speaks of "flaming potsherds raining from the sky."

Roughly 2000 years later, the Jewish astronomer Rabbi bar Nachmani created what could be considered the first impact theory: That Noah's Flood was triggered by two "stars" that fell from the sky. "When God decided to bring about the Flood, He took two stars from Khima, threw them on Earth, and brought about the Flood."

Another thread was woven into the tale when, in 1650, the Irish Archbishop James Ussher mapped out the chronology of the Bible -- a feat that included stringing together all the "begats" to count generations -- and put Noah's great flood at 2349 B.C.

All coincidence?

A number of scientists don't think so.

Mounting hard evidence collected from tree rings, soil layers and even dust that long ago settled to the ocean floor indicates there were widespread environmental nightmares in the Near East during the Early Bronze Age: Abrupt cooling of the climate, sudden floods and surges from the seas, huge earthquakes.

In recent years, the fall of ancient civilizations has come to be viewed not as a failure of social engineering or political might but rather the product of climate change and, possibly, heavenly happenstance. As this new thinking dawned, volcanoes and earthquakes were blamed at first. More recently, a 300-year drought has been the likely suspect.

But now more than ever, it appears a comet could be the culprit. One or more devastating impacts could have rocked the planet, chilled the air, and created unthinkable tsunamis -- ocean waves hundreds of feet high. Showers of debris wafting through space -- concentrated versions of the dust trails that create the Leonids -- would have blocked the Sun and delivered horrific rains of fire to Earth for years.

So far, the comet theory lacks firm evidence. Like a crater.

Now, though, there is this depression in Iraq. It was found accidentally by Sharad Master, a geologist at the University of Witwatersrand in South Africa, while studying satellite images. Master says the crater bears the signature shape and look of an impact caused by a space rock.

The finding has not been developed into a full-fledged scientific paper, however, nor has it undergone peer review. Scientist in several fields were excited by the possibility, but they expressed caution about interpreting the preliminary analysis and said a full scientific expedition to the site needs to be mounted to determine if the landforms do in fact represent an impact crater.

Researchers would look for shards of melted sand and telltale quartz that had been shocked into existence. If it were a comet, the impact would have occurred on what was once a shallow sea, triggering massive flooding following the fire generated by the object's partial vaporization as it screamed through the atmosphere. The comet would have plunged through the water and dug into the earth below.

If it proves to be an impact crater, there is a good chance it was dug from the planet less than 6,000 years ago, Master said, because shifting sediment in the region would have buried anything older.

Arriving at an exact date will be difficult, researchers said.

"It's an exciting crater if it really is of impact origin," said Bill Napier, an astronomer at the Armagh Observatory.

Napier said an impact that could carve a hole this large would have packed the energy of several dozen nuclear bombs. The local effect: utter devastation.

"But the cultural effect would be far greater," Napier said in an e-mail interview. "The event would surely be incorporated into the world view of people in the Near East at that time and be handed down through the generations in the form of celestial myths."

Napier and others have also suggested that the swastika, a symbol with roots in Asia stretching back to at least 1400 B.C., could be an artist's rendering of a comet, with jets spewing material outward as the head of the comet points earthward.

But could a single impact of this size take down civilizations on three continents? No way, most experts say.

Napier thinks multiple impacts, and possibly a rain of other smaller meteors and dust, would have been required. He and his colleagues have been arguing since 1982 that such events are possible. And, he says, it might have happened right around the time the first urban civilizations were crumbling.

Napier thinks a comet called Encke, discovered in 1786, is the remnant of a larger comet that broke apart 5,000 years ago. Large chunks and vast clouds of smaller debris were cast into space. Napier said it's possible that Earth ran through that material during the Early Bronze Age.

The night sky would have been lit up for years by a fireworks-like display of comet fragments and dust vaporizing upon impact with Earth's atmosphere. The Sun would have struggled to shine through the debris. Napier has tied the possible event to a cooling of the climate, measured in tree rings, that ran from 2354-2345 B.C.

Though no other craters have been found in the region and precisely dated to this time, there is other evidence to suggest the scenario is plausible. Two large impact craters in Argentina are believed to have been created sometime in the past 5,000 years.

Benny Peiser, a social anthropologist at Liverpool John Moores University in England, said roughly a dozen craters are known to have been carved out during the past 10,000 years. Dating them precisely is nearly impossible with current technology. And, Peiser said, whether any of the impact craters thought to have been made in the past 10,000 years can be tied back to a single comet is still unknown.

But he did not discount Napier's scenario.

"There is no scientific reason to doubt that the break-up of a giant comet might result in a shower of cosmic debris," Peiser said. He also points out that because Earth is covered mostly by deep seas, each visible crater represents more ominous statistical possibilities.

"For every crater discovered on land, we should expect two oceanic impacts with even worse consequences," he said.