Giant Tsunami Once Washed Over New York Area

Remember that huge tidal wave cresting over lower Manhattan in the 1998 asteroid-disaster movie "Deep Impact"?

Well, it really may have happened, but long before any skyscrapers were built — around 300 B.C., in fact.

Researchers from Columbia, Harvard and Vanderbilt universities first presented the hypothesis at a geologists' conference in December, and spoke more recently to the BBC.

Vanderbilt's Stephen Goodbred explained that an unusual eight-inch-thick layer of sea sand and gravel 2,300 years old lies along the shorelines and riverbanks of the entire New York metropolitan area.

Such a formation, containing chunks of rock as big as a fist, could only have been caused by a massive influx of sea water far inland — basically, a tsunami.

Surges of that size are mainly caused by two things — earthquakes or asteroid impacts. Yet there hasn't been much seismic activity along the Eastern Seaboard for millions of years.

Further examination of the sand layer showed microscopic diamonds and tiny, perfectly round bits of rock formed in the aftermath of a titanic explosion — both signs of an asteroid impact.

The real smoking gun would be a large offshore crater, but that would be hard to detect underwater. Nevertheless, the researchers are looking, convinced they're right.

"If we're wrong, it was one heck of a storm," Goodbred told the BBC.

• Click here to read more from the BBC.

• Click here for a longer examination in National Geographic News.

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