This goes back to as far as 35 million years ago; when a great chunk of Rock or it must have been Ice, slammed into what’s now the mouth of the bay, off Cape Charles, Virginia, hollowing out a 56-mile-wide (90- kilometer-wide) hole in the floor of the North Atlantic Ocean. But then we weren’t there to witness it.
This impact would 35 million years in the future help Scientists to discover the oldest body of sea water on Earth.

Modern day:
Some years ago, Scientists were drilling in the United States’ biggest crater when they accidentally tapped into the oldest body of seawater ever found. They weren’t expecting to find the ancient water, estimated to be some 100 to 145 million years old, while boring a hole 1.1 miles (1.8 kilometers) deep into the massive crater, located under the Chesapeake Bay

the bolide central crater and "annular ring" outside
Source: US Geological Survey (USGS) - Professional Paper 1622:

“The water was in the sediment long before the impact occurred. The impact simply reshuffled the sediment in large blocks, which helped preserve it,”


said study leader Ward Sanford, a hydrologist with the U.S. Geological Survey. The asteroid wallup also spawned gigantic tsunamis that possibly hit the Blue Ridge Mountains more than 100 miles (160 kilometers) away.  The seawater trapped deep underground is now in an area roughly the size of a large lake—about 60 square miles (155 square kilometers) across.

Source of the Story: National Geographic