Scientists have found the first evidence that a devastating meteor impact in the Middle East might have triggered the mysterious collapse of civilisations more than 4,000 years ago.
Studies of satellite images of southern Iraq have revealed a two-mile-wide circular depression which scientists say bears all the hallmarks of an impact crater. If confirmed, it would point to the Middle East being struck by a meteor with the violence equivalent to hundreds of nuclear bombs.
Today's crater lies on what would have been shallow sea 4,000 years ago, and any impact would have caused devastating fires and flooding.
The catastrophic effect of these could explain the mystery of why so many early cultures went into sudden decline around 2300 BC.
They include the demise of the Akkad culture of central Iraq, with its mysterious semi-mythological emperor Sargon; the end of the fifth dynasty of Egypt's Old Kingdom, following the building of the Great Pyramids and the sudden disappearance of hundreds of early settlements in the Holy Land.
Until now, archaeologists have put forward a host of separate explanations for these events, from local wars to environmental changes. Recently, some astronomers have suggested that meteor impacts could explain such historical mysteries.
The crater's faint outline was found by Dr Sharad Master, a geologist at the University of Witwatersrand, Johannesburg, on satellite images of the Al 'Amarah region, about 10 miles north-west of the confluence of the Tigris and Euphrates and home of the Marsh Arabs.
"It was a purely accidental discovery," Dr Master told The Telegraph last week. "I was reading a magazine article about the canal-building projects of Saddam Hussein, and there was a photograph showing lots of formations - one of which was very, very circular."
Detailed analysis of other satellite images taken since the mid-1980s showed that for many years the crater contained a small lake.
The draining of the region, as part of Saddam's campaign against the Marsh Arabs, has since caused the lake to recede, revealing a ring-like ridge inside the larger bowl-like depression - a classic feature of meteor impact craters.
The crater also appears to be, in geological terms, very recent. Dr Master said: "The sediments in this region are very young, so whatever caused the crater-like structure, it must have happened within the past 6,000 years."
Reporting his finding in the latest issue of the journal Meteoritics ;;amp Planetary Science, Dr Master suggests that a recent meteor impact is the most plausible explanation for the structure.
A survey of the crater itself could reveal tell-tale melted rock. "If we could find fragments of impact glass, we could date them using radioactive dating techniques," he said.
A date of around 2300 BC for the impact may also cast new light on the legend of Gilgamesh, dating from the same period. The legend talks of "the Seven Judges of Hell", who raised their torches, lighting the land with flame, and a storm that turned day into night, "smashed the land like a cup", and flooded the area.
The discovery of the crater has sparked great interest among scientists.
Dr Benny Peiser, who lectures on the effects of meteor impacts at John Moores University, Liverpool, said it was one of the most significant discoveries in recent years and would corroborate research he and others have done.
He said that craters recently found in Argentina date from around the same period - suggesting that the Earth may have been hit by a shower of large meteors at about the same time.