Sometime in the last 10,000 years, a gigantic space rock plummeted into the Indian Ocean, creating a mega-tsunami of massive proportions. Colossal waves enveloped the coast of Africa and left what we see today as chevrons, or wedge-shaped sediment deposits, in Madagascar.
But did this actually happen? One might think that geological breadcrumbs are easy to spot, but it’s quite the contrary: As ancient mega-tsunamis wash away, researchers are left looking for signs that they were ever there, or to the contrary, that they were never there to begin with.
The debate is neatly summed up by geologist Dallas Abbott: "While most researchers have assumed that the sand in the dunes was transported inland by the wind, we instead have proposed that the deposits are from a mega-tsunami event."
Recently, at the American Geophysical Union meeting in San Francisco, Abbott cast new evidence into the debate: She and her colleagues found 22 samples from two dunes in Madagascar that showed high levels of carbonate, which were dated to around 10,000 years ago.
The carbonate primarily came from marine microfossils, which is why the researchers say their evidence adds weight to the mega-tsunami theory. Since the cliffs are 175 meters (574 feet) high, a wave would need to be nearly 90 meters (295 feet) to leave such deposits – no mean feat.
Many researchers, however, remain skeptical of her evidence: They say plenty of these regions have carbonate sand and that a local source can’t be ruled out. Joanne Bourgeois, a sedimentary geologist at the University of Washington, is one such contender. She proposes another possibility for the chevron: wind.
In 2009, she modeled the likely path that waves produced by a space rock crashing into the Indian Ocean would take. She found that the orientation of many of the chevrons were inconsistent with the model. If a mega-tsunami did happen, the chevrons should be perpendicular to the coast; many of them, however, were parallel.
"And if it really was from an impact, you should find evidence on the coast of Africa too, since it is so near," said Bourgeois in a 2009 statement. Now, in an update to the National Geographic, she has added: "I have no reason to reconsider our analysis. The evidence presented is unconvincing for a mega-tsunami hypothesis."
Abbott still contends the age of the fossils support her side of the debate. Not only that, but if the fossils were blown by wind to their final resting place, they would have been powder by the time they landed.
While the dispute continues to ensue, as all good scientists know, a healthy debate in science never goes amiss.
[H/T: National Geographic]
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