Great Comets, Great Floods

This column's topic was dictated by a concatenation of coincidence--otherwise, known as fate, or luck. Consider: in mid-July 1994, much of the state of Georgia was submerged under the rainy aftermath of a tropical storm, while parts of Alaska's Interior were drying out after their own mini-deluge. Meanwhile, the shards of a big comet descended into the atmosphere of Jupiter, there generating explosive releases of energy equivalent to nuclear megatonnage.

Naturally, this was the perfect time for Geophysical Institute Professor David Stone to hand me a scientific article that considers the possible link between a broken-up comet and a great flood. Not just any great flood, either. Authors Edith Kristan-Tollmann and Alexander Tollmann, both of the University of Vienna's Geological Institute in Austria, suggest that a cometary crash is the cause of the flood we usually associate with Noah.

So many cultures have tales of catastrophe by flood among their beliefs that some psychologists take the flood as a universal symbol, an image standing in for some pervasive but individually felt human experience, such as the trauma of being born. The Tollmanns believe instead that the tales represent a historical experience, an overwhelming event that befell groups of people at different places around the world.

For those who believe in conservatively interpreting a religion that includes the Flood among the items of received wisdom, this attitude would seem only right and natural. But the nature of faith is such that a belief can be held onto without any evidence to support it, or even in spite of evidence to the contrary. Science demands supporting evidence, and the Tollmanns are scientists. Their article musters the evidence they have found.

Their speculation within the confines of science is possible because of others' research. Over the past 200 years, cultural anthropologists have recorded the legends and religious traditions of most cultures around the world. Within the past 50 years, geologists have developed the crucial ideas and methods to understand what the evidence in the stone means. And within the past 15 years or so, everyone has come to know a great deal more about the evidence left by giant impacts, thanks to the intense work on the Cretaceous/Tertiary boundary that marked the demise of the dinosaurs.

By combining historical record with geological clues, the Tollmanns picture several cometary fragments--probably seven of them--smacking into the earth about ten thousand years ago. The great splashdown took place near the autumnal equinox in the Northern Hemisphere, spring in the Southern, with the major fragments hitting the oceans over a span of days at most. (Oddly, the Tollmanns are less certain of the year than of the time of year; because of the many internal clues in the tales and commentaries worldwide, Mesopotamian and Scandinavian sources agree on the season.)

The scientists' interpretation of the legends in light of modern geological knowledge does require some leaps into faith or at least poetry: "The Chinese motif of the dragon may provide an impressionistic rendering of the impact in the southern China Sea," they write. "The dragon itself symbolizes the tail of the comet, deformed by the currents in the atmosphere," and so forth.

The geologic evidence is--or should be--less arguable. The Tollmanns think they've found described in the scientific literature a worldwide array of tektites of the right age, for example. Tektites are rocks melted by an impact and splashed away as molten drops that then solidify again as they cool. Because they are inorganic, they are usually dated by stratigraphy--the age of the layers within which they lie--and that is an admittedly imperfect science.

Scientists may identify other flaws, but meantime the Tollmanns' hypothesis is fine to muse upon while watching the waters rise.