Did Asteroid Cause Ancient N.Y. Tsunami?

Nov. 20, 2008 -- Long before New York City was the Big Apple, or even New Amsterdam, a giant tsunami crashed ashore.

It was 2,300 years ago. The Palisades that frame the Hudson River were whisper-quiet, the sandy beaches of Long Island and New Jersey empty, and Manhattan was still just an unbroken sylvan carpet.

Then came the mammoth wave, roaring into the serenity. No one knows for sure what caused it, but new clues found in the Hudson's silt suggest an asteroid 100 meters (330 feet) in diameter slammed into the Atlantic Ocean nearby.

WATCH VIDEO: See how a 65-foot wave could inundate New York City.

While sifting through samples, Katherine Cagen of Harvard University and a team of researchers found carbon spherules -- perfectly round particles that form in the extreme pressures of an impact.

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"But the main thing that closes the deal is that we looked in the spherules and found nano-diamonds," said Dallas Abbott of Columbia University, a co-author on the work. "These have only been found in impact ejecta or in meteorites."

The team found grains of several shocked minerals in the sediments as well, but the discovery remains controversial.

"To get a wave 2.5 meters high that far up the Hudson, you need a wave 20 meters high at Manhattan," said Steven Ward of the University of California, Santa Cruz. "It would've gone several hundred meters inland on Long Island; you should see evidence of this thing all over the place."