Ancient Mesopotamia

...and the seven judges of hell... raised their torches, lighting the land with their livid flame. A stupor of despair went up to heaven when the god of the storm turned daylight into darkness, when he smashed the land like a cup.

So says an account of the Deluge from the Epic of Gilgamesh, circa 2200 BC.

Similar but considerably less powerful versions of the events which some scientists say brought down the world's first civilisations happen frequently, when meteors hit the planet.

Biblical stories, apocalyptic visions, ancient art, and scientific data all seem to intersect at around 2350 BC, when one or more catastrophic events wiped out several advanced societies in Europe, Asia, and Africa.

Increasingly, some scientists are suspecting that 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.

A three kilometre-wide crater in Iraq, newly found by 2001's standards, was spotted somewhat serendipitously in a perusal of satellite images, and it was this which was held up as a possible smoking gun. The crater's discovery, which was announced in a 2001 issue of the Meteoritics & Planetary Science journal, was a preliminary finding. Scientists were stressing that a ground expedition would be needed to determine whether the landform was actually carved out by an impact.

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

Too many coincidences

Archaeological findings seem to have shown that, in the space of a few centuries, many of the first sophisticated civilisations disappeared.

The Old Kingdom in Egypt fell into ruin. The Akkadian culture of Mesopotamia, possibly the world's first empire, collapsed. Settlements in the ancient Levant, gone. Mesopotamia, Earth's original breadbasket, dust [1].

At around the same time - a period known as the Early Bronze Age - apocalyptic writings appeared, fuelling religious beliefs which persist today.

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

Roughly two thousand 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' which 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 which included stringing together all the 'begats' in order to be able to count generations, and put Noah's great flood at 2349 BC [2].

All coincidence? A number of scientists were beginning to think not.

Mounting hard evidence which had been collected from tree rings, soil layers, and even dust which long ago settled to the ocean floor was indicating 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.

Comet as a culprit

In recent years, the fall of ancient civilisations 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 three hundred year-long drought became the likely suspect.

But now more than ever, it was becoming apparent that a comet could have been the culprit. One or more devastating impacts could have rocked the planet, chilled the air, and created unthinkable tidal waves, ocean waves which were tens of metres high. Showers of debris wafting through space, concentrated versions of the dust trails which also created the Leonid meteor shower, would have blocked out the sun for years and delivered horrific rains of fire on Earth.

So far, the comet theory lacks firm evidence, such as the discovery of a crater.

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

The finding had not been developed into a fully-fledged scientific paper, however, nor had it undergone peer review. Scientists 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 needed to be mounted to determine whether the landforms did in fact represent an impact crater.

Researchers would look for sherds of melted sand and telltale quartz which 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 vaporisation as it screamed through the atmosphere. The comet would have plunged through the water and dug into the earth below.

If it proved to be an impact crater there would be a good chance that it had been dug from the planet less than six thousand years ago, Master said, because shifting sediment in the region would have buried anything older.

Arriving at an exact date would 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.

Cultural impact

Napier said an impact which 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,' he added in an email 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 which has roots in Indo-Iranian steppe culture as a symbol of peace stretching back to at least the second millennium BC, could be an artist's rendering of a comet, with jets spewing material outwards as the head of the comet points earthwards.

But could a single impact of this size take down civilisations on three continents? Most experts thought it was unlikely.

Napier was of the opinion that multiple impacts, and possibly a rain of other smaller meteors and dust, would have been required. He and his colleagues had been arguing since 1982 that such events were possible. He also added that it may have happened right around the time at which the first urban civilisations were crumbling.

Napier though a comet named Encke, which had been discovered by scientists in 1786, is the remnant of a larger comet which broke apart five thousand years ago. Large chunks and vast clouds of smaller debris were cast into space. Napier said it was possible that the planet 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 vaporising upon impact with Earth's atmosphere. The sun would have struggled to shine through the debris. Napier tied the possible event to a cooling of the climate, which was measured in tree rings which ran from 2354-2345 BC.

Supporting evidence

Though no other craters had been found in the region by 2001 and precisely dated to this time period, there was other available evidence to suggest that the scenario could be plausible. Two large impact craters in Argentina were believed to have been created sometime in the past five thousand 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 ten thousand years. Dating them precisely is nearly impossible with the technology available at the start of the new millennium. And, Peiser said, it was unclear whether any of the impact craters which were thought to have been made in the past ten thousand years could be tied back to a single comet.

But he did not discount Napier's scenario.

'There is no scientific reason to doubt that the break-up of a giant comet may result in a shower of cosmic debris,' Peiser said. He also pointed out that, because Earth is covered mostly by deep seas, each visible crater represents more ominous statistical possibilities. 'For every crater which is discovered on land we should expect two oceanic impacts with even worse consequences,' he said.

Tidal waves generated in deep water can rise even higher when they reach a shore.

Reverberating today

Peiser was studying known craters for clues to the past. But he also examined religions and cults old and new for signs of what may 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 said 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 the existence of apocalyptic religions of today to be able to understand the far-reaching consequences of historical impacts,' he said. 'After all, the apocalyptic fear of the end of the world is still very prevalent today and can often lead to fanaticism and extremism.'

An obsession with the end of the world provides the legs on which modern-day terrorism stands, Peiser argued. Leaders of fundamentalist terror groups drum into the minds of their followers looming cataclysms which are inspired by ancient writings. Phrases run along these lines: a rolling up of the sun, darkening of the stars, movement of the mountains, splitting of the sky...

It is within 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 instil '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.'

No smoking gun yet

Despite the excitement of the newfound hole in the ground in Iraq (in 2001), it was still far from clear why so many civilisations collapsed in such a relatively short historical timeframe. Few scientists, even those who were finding evidence to support the idea, were (or are) ready to categorically blame a comet.

French soil scientist Marie-Agnes Courty who, in 1997, found material which could only have come from a meteorite and dated it to the Early Bronze Age, urged caution when drawing any conclusions until a smoking gun could be 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 which are to be found in real climate and geologic data. The initial impact, if it is on land, vaporises life for kilometres 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 climate effects is not known for sure because scientists have never witnessed such an event.

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

Mike Baillie, a professor of palaeoecology at Queens University in Belfast, suspected that 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 agricultural-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 civilisations.'

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

Lessons for tomorrow

Either way, there is a giant scar on the planet, near the cradle of civilisation, which could soon begin to provide some solid answers, assuming geologists could get permission to enter Iraq and conduct a study (a possibility which has certainly be delayed by many years due to the conflict in Iraq).

'If the crater dated from the third millennium BC, it would be almost impossible not to connect it directly with the demise of the Early Bronze Age civilisations in the Near East,' said Peiser.

Perhaps before long all the cometary traditions, myths and scientific fact will be seen to converge at the Iraqi hole in the ground for good reason. Understanding what happened, and how frequent and deadly such impacts may be, is an important tool for researchers like Peiser who aim to estimate future risk and help modern society to avoid the fate of the ancients.

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

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