NEW YORK (AP) — It's a ship tied to two critical points in American history: Sept. 11, 2001, and the eve of the Revolutionary War.

Researchers said this week that a vessel unearthed four years ago at the World Trade Center site in Lower Manhattan was made from wood cut around the year 1773 — two years before the start of the war and three years before the signing of the Declaration of Independence.

Scientists at Columbia University's Lamont-Doherty Earth Observatory, writing in the July issue of the journal Tree Ring Research, said the white oak in the ship's frame came from a Philadelphia-area forest and matched the material used to build the city's Independence Hall.

They said they tentatively identified it as a Dutch-designed, Philadelphia-built sloop made to carry passengers and cargo over shallow, rocky water.

They said it sailed for 20 to 30 years before being weighed down and sunk to the bottom of the Hudson River as landfill to extend lower Manhattan.

A 32-foot piece of the vessel was found in July 2010 about 20 feet under a street during construction of a parking garage for the new 1 World Trade Center tower, part of the complex rebuilt after the 9/11 terrorist attacks took down two towers.

Archeologists dismantled the ship piece-by-piece and freeze-dried each plank so they could be studied and eventually reassembled for display.

A 100-pound iron anchor was found a few yards from the hull, possibly from the old vessel.

It was the second ship found buried in Lower Manhattan in the last four decades. Archaeologists found an 18th-century cargo ship on Water Street in 1982.