Ancient seawater found under Chesapeake Bay

The oldest body of seawater ever identified is buried under the Chesapeake Bay.

According to the U.S. Geological Survey (USGS), this recently discovered body of water dates back to the Early Cretaceous period, when wet and dry seasons controlled the climate, tropical jungles dominated the landscape and dinosaurs were becoming more plentiful.

The water is buried beneath a large meteorite that struck the earth 35 million years ago, throwing debris into the atmosphere and spawning a train of tsunamis that probably reached as far as the Blue Ridge Mountains. The so-called “Chesapeake Bay impact crater” is the largest crater discovered in the United States and helped determine the current shape of the Bay.

Because the water is trapped in place, USGS scientists have been able to estimate its age—100 to 145 million years old—and its salinity—twice as salty as modern seawater.

Acting USGS Associate Director for Water Jerad Bales said in a media release that before this discovery was made, no one realized that the saltier-than-normal groundwater found deep in the Atlantic Coastal Plain “was North Atlantic ocean water that has essentially been in place for 100 million years.”

“We are working directly with seawater that dates far back in earth’s history,” Bales said.

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