Plotting the distribution of great flood myths together with specific reported phenomena like directions from which great winds blew or tsunamis came, Masse finds that the most efficient way to account for them is by positing a very large comet impact in the central or southern Indian Ocean. This might not account very well for flood myths in the Americas, but Masse thinks that flooding there could have resulted from partial disintegration of the incoming comet, with two or more pieces falling on different parts of the earth over a period of hours or days. Some of the myths speak of multiple events happening in close succession. But the really big impact, he thinks, the most lethal of the bunch, occurred somewhere south of Madagascar.
Where, it turns out, there is a possible impact crater on the sea floor 1500 kilometers southeast of Madagascar. Named Burckle Crater and discovered only recently by Masse's colleague Dallas Abbott from Lamont Doherty Earth Observatory, it is a little under 30 km in diameter and is visible on bathymetric maps. Stratigraphic cores taken near there suggest that it is an impact crater, but are not definitive. The Burckle Crater needs more study, but it is 3800 meters deep, so it's not an easy place to explore. More readily accessible is the southern coast of Madagascar where recently studied chevron-shaped dune deposits of potential tunamic origin may be indicative of giant waves more than 200 meters in height. Masse and Abbott have joined together with more than 25 other scientists to form the "Holocene Impact Working Group," to better explore Burckle Crater, Madagascar, and other locations bearing potential Holocene physical evidence of impact.
If Masse is right, a comet impact big enough to have devastating effects on human civilization occurred in 2807 BC--a bit under 5,000 years ago. Other smaller impacts and airbursts have happened since then--the most recent being at Sikhote Alin near Vladivostok in 1947. None of these were as devastating as the K-T event that doomed the dinosaurs, but many were big enough to wipe out cities or whole nations if there had been any in the vicinity at the time. And the 2807 BC event, to judge from the myths, made the December 2004 Indian Ocean tsunami look like a ripple on the beach.
The Past as Prologue
Would confirmation of a civilization-killing impact 5,000 years ago mean that another one is likely tomorrow or the next day? No, but the more large impacts there have been in the recent past, the more troubling become our prospects for the future. In fact, in the November 2007 issue of the Proceedings of the National Academy of Sciences, physicist Richard Firestone and colleagues suggest that the major climatic perturbations and extinctions at the beginning of the Younger Dryas event some 12,900 years ago were caused by an comet impact even more catastrophic than that of the 2807 BC event.
Masse's research highlights the importance not only of studying Earth's past for evidence of impacts, but of searching space for the NEOs that may be incoming. It also shows that when it comes to identifying impacts that have occurred over the last few thousand years, geophysical research isn't the only game in town. Archaeology and the study of humankind's oral traditions have unique contributions to make as well.
This article is a part of the About.com guide to the Climate Change and Archaeology.