As the story is told in the Old Testament, the great flood lasted for 40 days and 40 nights, and submerged every living thing on Earth beneath 24 feet of water, sparing only Noah, his family and the pairs of animals he protected on his ark.

Scientists have never found Noah or his ark, but they believe in his flood. It happened about 7,600 years ago, when the Mediterranean Sea, swollen by melted glaciers, breached a natural dam separating it from the freshwater lake known today as the Black Sea.

It was an apocalyptic event, in many respects much worse than anything described in Genesis. Every day for two years, 10 cubic miles of sea water cut through the narrow channel now known as the Bosporus, and plunged into the lake -- more than 200 times the flow over Niagara Falls. Every day the lake level rose six inches.

And every day the water marched another mile inland, forcing people and animals to flee or drown, killing freshwater fish and plants by the ton, inundating forests, villages and entire cities and spreading pestilence and death for miles.

But as the deluge filled the lake and transformed it into a sea, it also created an ecosystem unique in the world -- an oxygenless abyss where shipwrecks could rest for thousands of years in chill, inert darkness uncorrupted by living creatures.

The possible presence of old ships in near-mint condition on the Black Sea floor has made Noah's flood the starting point for perhaps the most ambitious project ever undertaken in the emerging field of deep-water archaeology.

Since explorer Robert D. Ballard discovered the Titanic 12,500 feet beneath the North Atlantic in 1985, deep-sea experts have used ever more sophisticated robots and submersibles to plumb the world's seas for both science and profit.

Secrets that have withstood prying eyes for hundreds or even thousands of years are being unlocked in a new age of discovery reminiscent of the early days of space travel.

In 1988, commercial salvagers found perhaps $1 billion in gold in the 19th century paddle wheeler Central America, sunk in deep water off the North Carolina coast. In 1998, Tampa-based salvagers found a 2,500-year Phoenician cargo ship off Gibraltar.

In 1989, Ballard found the German battleship Bismarck, sunk by the British in 15,600 feet of water during World War II, and this summer he found two ships nearly 3,000 years old lying more than 1,000 feet below the surface of the Eastern Mediterranean.

But the "Black Sea Project," with Ballard as lead oceanographer, has far more audacious goals than the discovery of a single ship. The project hopes to prove that literally thousands of years of history may lie intact in the shipwrecks that are blanketed by the sterile waters of Noah's flood.

"It's very much like a bathtub, but without a drain," Ballard said. "The Bosporus acts like an overflow valve, but the trapped water can't circulate, so it went anoxic [lost its oxygen] long ago. Such conditions exist nowhere else in the world."

In the past five years, project researchers trying to determine the Black Sea trade routes of antiquity have studied scientific literature, history and classical texts such as the myth of Jason, whose quest for the Golden Fleece is believed to have made him the first of the ancient Greeks to enter the Black Sea.

At project headquarters in the Turkish city of Synope, archaeologists mapped a seaport that acted as a major trading center during the Bronze Age, 5,000 years ago, and maybe even earlier. Artifacts have linked Synope to Black Sea sites north in the Crimea and west in Bulgaria, as well as to Troy, the fabled Aegean city that guarded the entrance to the Black Sea.

Rather than hugging the coast, the research suggests, sailors were willing to save time and money by traveling point-to-point over waters reaching depths close to 7,000 feet.

"Once an ancient mariner got into water beyond visual depth, he didn't know how deep it was," Ballard said. "Here you've got a trade route that can be documented as far back as any."

And just this summer, the project's underwater surveyors found an ancient coastline at a depth of 450 feet, just above the anoxic dead zone: "I'm not sure whether it's Noah's flood, or not Noah's flood," said David Mindell, a Massachusetts Institute of Technology professor leading the marine survey. "But I do buy that there was a flood."

In the early days of deep sea archaeology, a complex, multidisciplinary effort like the Black Sea Project would have been unthinkable. Only governments and large corporations could afford to invest in the technology, used principally for mineral prospecting, pipeline maintenance and military intelligence.

But since the Titanic discovery, the tools of the trade have improved dramatically, as has the technical expertise of those who use them. And where engineers once jealously guarded their recovery techniques, today's explorers can purchase much of the machinery, including the basic robot, known as a "remotely operated vehicle" (ROV), off the shelf.

"It's getting to the point where virtually anybody can go down and look," said Greg Stemm, whose Tampa-based Odyssey Marine Exploration Inc. found the ancient Phoenician wreck off Gibraltar while searching for a British treasure ship. "ROVs are like buying a new computer. You want to wait as long as you can before committing."

The theory of the Black Sea's Neolithic catastrophe was developed by Columbia University marine geologists William Ryan and Walter Pitman over three decades of research and published this year in their book "Noah's Flood."

The authors describe how the sea level worldwide began to rise as glaciers melted at the end of the last ice age 15,000 years ago. When the melt began, the Black Sea was a freshwater lake fed by rivers, among them those known today as the Danube, the Dnieper and the Don.

On the lake's southern edge, a 360-foot natural dam held back the waters of what is now the Mediterranean Sea. By 7,600 years ago, sea level probably had risen to within 15 feet of the lip of the Bosporus. And then it flooded.

"It probably started as a trickle when it pierced the Bosporus valley," Pitman said in an interview. "But when it got to the Black Sea, it gouged out a channel, and within 60 days it began to flood with a rush."

It was a one-of-a-kind event, and it had a unique result. The incoming salt water, denser than the fresh water it displaced, plunged straight to the bottom of the lake bed. As the seawater rose, the fresh water floated on top, and, being less dense, stayed on top, flowing in from the northern rivers and out via the Bosporus.

This bathtub phenomenon repressed the natural heat exchange that causes water to circulate and reoxygenate in seas and lakes throughout the world. Trapped on the bottom, the creatures that lived in the original floodwater used up the original oxygen, then died.

Today, the top 450 feet of the Black Sea are constantly renewed and support a vigorous marine life. But the abyss, leached of oxygen long ago, lies like a cold blanket thousands of feet deep covering the sea floor and its secrets.

If there is no oxygen, then there should be none of the wood-boring mollusks that consume wooden ships at almost any depth. Marine archaeologists learned long ago that in ordinary circumstances, an old wooden wreck will appear as nothing more than a jumble of amphorae or other cargo on the sea bottom. Part of the hull may be intact if it has sunk into the mud, but exposed wood will have been eaten.

But in the Black Sea, anything on the bottom should be intact -- including ancient wooden ships. And because the Black Sea lies within shouting distance of the Fertile Crescent and served as a commercial waterway for civilizations from ancient Greece to Byzantium and the Ottoman Empire, the possibilities are dazzling: "One should have a complete chronicle of human history," Ballard said.

This was the pitch he made in 1994 to archaeologist Fredrik T. Hiebert, a specialist in ancient trade along the "silk road" linking central Asia with the West. If Hiebert could find a trade route across the Black Sea, Ballard said, then deep water archaeology could find the wrecks: "This was the most incredible thing I had ever heard," Hiebert said. "The only problem was that the Black Sea is huge."

Hiebert agreed to oversee a series of library studies to determine what trade existed and found solid evidence that the ancient peoples on all sides of the waterway had a brisk interchange of goods.

Along the coast, whether in Synope or modern Ukraine or Russia, artifacts showed remarkable similarities. Roof tiles in the Crimea were stamped with the Greek word "Synope," and studies of ocean currents and winds showed that sailors could travel the 180-mile south-north route across the sea from Synope to the Crimea, and probably did. But it was dangerous, Hiebert said: "Roman historians wrote about it."

Funded by the University of Pennsylvania and the National Geographic Society, Hiebert, a Penn archaeologist, and Ballard began work on the project. Hiebert, in charge of dry land archaeology, mapped the land site, while Mindell managed the marine survey.

"We were already up and running because of the anoxic water and the shipwrecks," Mindell recalled, but then "Noah's Flood" was published, with its suggestion that entire cultures may lie submerged below the ancient floodwaters.

The group expanded its mandate to include a search along the old coastline. Next year, Hiebert will spot likely locations for ancient settlements, and Mindell will look for them.

Meanwhile, Ballard will use the government's ROV "JASON" to begin scouting the old trade route, aided by a narrow-beam sonar developed by Mindell that can discern a wreck through up to 12 feet of sediment.

Perhaps then, Ballard said, the team will be able to answer its most important question: Have the wood-borers figured out a way to work in the Black Sea abyss, "or do the wrecks have sails?"

An Epic Flood

About 7,600 years ago, melting glaciers forced the Mediterranean Sea to breach a natural dam (a) separating it from what is now known as the Black Sea.

Each day for two years, 10 cubic miles of ocean water flowed into what was then a fresh water lake, transforming it into a sea whose depths support no life (b).