Fossil shore lines show recent Flood

Beginning with the key discovery of fossil shorelines in the Black Sea about 100 metres below global sea level, this book highlights a remarkable event in oceanographic history. The reconstruction of this geological calamity is based on sound observations and radiocarbon datings. The fossil discovery would not be surprising if the shorelines dated from the last glacial period (18,000-24,000 years ago), when sea level globally stood that low, but William Ryan and Walter Pitman found ages of only 7,500 years. At that time, the continental ice sheets had already melted, so that global sea level had risen to its present mark and the Bosporus Strait would have been open - if indeed it existed. Ryan and Pitman demonstrate that this was not the case, and that the Black Sea remained isolated from the ocean. They propose that catastrophic failure of the Bosporus "dam" about 7,500 years ago caused a sudden rise of the Black Sea surface to global sea level. The 100-metre rise would have been accomplished at a rate of some 15cm per day. In coastal regions, people would have had to move a kilometre each day for two years to avoid the onslaught. The book links the consequent migrations to the observed dispersion of new cultures and agricultural techniques throughout Eurasia and likens the rise of the Black Sea to the flood in the legend of Gilgamesh, the precursor story of Noah's flood.

The book opens with summaries of the developments in archaeology and geology that allowed a reconstruction of the events and their possible relationship to the mythical floods. The discovery of the legend of Gilgamesh is presented, as is the discovery of global ice ages. A brief chapter introduces the principles of water exchange between the Black Sea and the Mediterranean through the Bosporus. Next, a well-known desiccation and re-fill event is discussed (the so-called Messinian salinity crisis), which took place 5 million years ago. At that time, the entire Mediterranean dried up, leaving enormous evaporite deposits and causing the formation of soils (including roots) at places that today are submerged under hundreds or thousands of metres of seawater (see also Ken Hsu's The Mediterranean Was a Desert ). This desiccation ended abruptly when movement along an Atlantic fault opened up the Strait of Gibraltar, causing a catastrophic refill of the Mediterranean to global sea level. This event, which was orders of magnitude more dramatic than the Black Sea events of 7,500 years ago, is presented to illustrate the feasibility of such exceptional processes. It is an example of a theme familiar to researchers of climate and ocean change on geological time-scales. All that might happen in the near future has occurred more dramatically in the geological past. For example, when dinosaurs ruled the world, atmospheric CO² levels were two to four times higher than today, while sea level stood some 200 metres higher. Studying the past, therefore, provides a vital insight into potential future change.

The book continues with a description of the authors' quest for evidence to support the story of Noah's flood. Noting that the flood of 5 million years ago was too early to have affected mankind, they discover that Black Sea sediment records contain a dramatic change within human time-scales, caused by evaporative draw-down to 100 metres below global sea level and subsequent flooding. The draw-down is viewed within the context of climatic changes during the aftermath of the last glacial maximum, which was punctuated by episodes of extreme aridity throughout Eurasia. From the time of the glacial maximum until the catastrophic flooding, the Black Sea was more a "Black Lake": a basin filled with fresh mel****er from the great continental ice-sheets. The catastrophic flooding event represents the first invasion of marine (Mediterranean) water with its distinct biota. Radiocarbon dating of the inundation surfaces provides a stunningly consistent age for the flood, about 7,500 years ago. The final piece of the puzzle was then put into place by Bob Karlin, who identified a massive submarine avalanche just inside the Black Sea near the Bosporus. It suggested a sudden and violent incursion of Mediterranean waters through a newly opened passage.

Ryan and Pitman then embark on an archaeological voyage, reviewing changes in early societies in the Levant, Anatolia and Eurasia. They argue in favour of an "oasis" model, according to which early societies survived harsh arid episodes, such as the Younger Dryas (11,500-12,500 years ago) by migrating to locations where water remained available. Within this context, they highlight the desertion and repopulation of early settlements in the Anatolian highlands, caused by a cold event about 8,000 years ago. This event would have driven migration from the highlands and settlement on Black Lake's lowland shores.

The authors do not elaborate on the relationship between the two cold and arid events. Here, however, it is interesting to note that the Younger Dryas and the "8 ka" event are part of a sequence of cold and arid events recognised throughout the northern hemisphere. Similar events took place about 6,000 years ago, 4,000 years ago (collapse of the Akkadian empire), 2,600 years ago and 1,500 years ago. The global timing and nature of such events formed the focus of a workshop of 53 international specialists in climate variability on (sub-)millennial time-scales in Trins, Austria, this year. This confirmed that, at least since 80,000 years ago, significant variability has occurred with
an average cyclicity of 1,500 years, although this periodicity was more irregular after the disappearance of the northern ice sheets about 10,000 years ago. Some researchers argued that the most recent example was the "Little Ice Age", about 350 years ago, the period that gave rise to the famous European paintings of extreme winter scenes (for example, Bruegel the Younger's Winter Landscape ). Other scientists considered the Little Ice Age too weak and too early in the cycle, in which case the next climatic deterioration should be expected in the near future. Importantly, there was general agreement that the onset and termination of these cold and arid episodes are very abrupt (occurring within decades). Consequently, their impact on the environment and societies is enormous. This would be true for past societies, but arguably even more so for present-day societies, with high population, territorial restrictions to migration, and reliance on transport infrastructure and centralised food production.

Ryan and Pitman trace dispersions of cultures and widespread genetic similarities to a diaspora triggered by the flooding of the Black Sea coasts when the Bosporus dam broke about 7,500 years ago. The variety of flood myths in many cultures might then be traced to a common source: the Black Sea flood. The book ends with a fictional rendition of a flood legend in Assyria.

Thus, Ryan and Pitman give a romantic twist to a book full of geological facts and archaeological observations, and it is captivating from beginning to end. There is an impressive bibliography that will help interested readers find their way into the more detailed background. Although there could have been a bit more attention to events in the Mediterranean on the other side of the Bosporus Strait, the book is highly entertaining and educational. If you liked Fingerprints of the Gods, Noah's Flood should be part of your collection.

Eelco J. Rohling is senior lecturer in oceanography, University of Southampton.