Seawater from early Cretaceous period found under Chesapeake Bay

Not only is the Chesapeake Bay in the United States so enormous it can be seen from space, it essentially came from outer space.

An asteroid or huge chunk of ice slammed into earth about 35 million years ago, splashing into the North Atlantic sea and sending tsunami as far as the Blue Ridge Mountains. It left a 90-kilometre-wide hole at the mouth of what is now the bay.

But a newly published research paper written by US Geological Survey scientists shows that wasn't the end of it. While drilling holes in southern Virginia to study the impact crater, the scientists discovered "the oldest large body of ancient seawater in the world", a survivor of that long gone sea, about 800 metres underground near the bay.

"What we essentially discovered was trapped water that's twice the salinity of [modern] seawater," said Ward Sanford, a USGS hydrologist. "In our attempt to find out the origin, we found it was early Cretaceous seawater. It's really water that's from the North Atlantic."

The findings showing that the water is probably between 100 million and 150 million years old were published on Thursday in the journal Nature.

The Chesapeake Bay Impact Crater was discovered in 1999 by a tandem of USGS and Virginia Department of Environmental Quality scientists.

They theorised that a huge rock or chunk of ice slammed into an ancient ocean, sending enormous pieces of debris skyward and forcing monster tsunami hundreds of kilometres inland. Over centuries, the crater became hidden under 120 to 36- metres of sand, silt and clay, hampering its discovery.