Ship House, Russia

Origin of flood myths
Adrienne Mayor's The First Fossil Hunters and Fossil Legends of the First Americans promoted the hypothesis that flood stories were inspired by ancient observations of seashells and fish fossils inland and on mountains. The ancient Greeks, Egyptians, Romans, and Chinese all wrote about finding such remains in these locations, and the Greeks hypothesized that Earth had been covered by water several times, noting seashells and fish fossils found on mountain tops as evidence. Native Americans also expressed this belief in their early encounters with Europeans, though they had not written it down previously. However, Leonardo da Vinci postulated that an immediate deluge could not have caused the neatly ordered strata he found in the Italian Apennines.
Some geologists believe that quite dramatic, unusually great flooding of rivers in the distant past might have influenced the legends. One of the latest, and quite controversial, hypotheses of this type is the Ryan-Pitman Theory, which argues for a catastrophic deluge about 5600 BC from the Mediterranean Sea into the Black Sea. This has been the subject of considerable discussion, and a news article from National Geographic News in February 2009 reported that the flooding might have been "quite mild".