Many scientists accept the idea that the biblical story of Noah's flood was inspired by a sudden inundation of the Black Sea by the Mediterranean 7500 years ago. But new research suggests no such flood occurred.
Geologists Bill Ryan and Walter Pitman of Columbia University crafted the "Noah's Flood Hypothesis" in 1997 to explain the sudden appearance of saltwater mollusks in 7500-year-old Black Sea sediments. They proposed that during the last Ice Age, some 18,000 years ago, sea levels dropped enough to isolate the Black Sea from the Mediterranean Sea. Rain and rivers then turned the Black Sea basin into a brackish lake. As the climate warmed, melting glaciers slowly refilled the Mediterranean. When it burst through the Bosporus Strait, the Black Sea was suddenly flooded with saltwater.
Now a group of geologists led by Ali Aksu of Memorial University of Newfoundland suggest in an upcoming issue of Marine Geology that the Black Sea was already full of fresh water, and that the saltwater flood was more of a trickle. The team looked at seismic profiles taken midway between the Mediterranean and Black Seas. At least 10,000 years ago, according to the profiles, fresh water flowed out of the Black Sea forming a delta. And cores drilled into the Bosporus sediment hinted that the water at the bottom of the strait lacked oxygen. When this happens in modern estuaries, it's because the salty bottom water is trapped below fresh water.
Aksu's team reasons that around 9000 years ago, the rising global sea levels pushed an undercurrent of salt water through the Bosporus into the Black Sea--replacing the fresh water still flowing out. Because the salt water would sink below the fresh and fill the Black Sea from the bottom up, Aksu believes mollusks arrived 7500 years ago when the level of salty water rose to the hundred meter depths where mollusks thrive.
The new scenario has convinced David Piper of the Geological Survey of Canada in Dartmouth, Nova Scotia. "It seems to me these observations make the flood hypothesis impossible," he says. But Bill Ryan and others aren't persuaded. Ryan points out that there are 9000-year-old beach deposits 100 meters beneath the surface Black sea, which suggests that the sea dried up again after the delta formed.