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Nov 21, 2013 05:36 PM EST

Who Knew Water Could Be So Old: Scientists Discover Ancient Seawater In Chesapeake Bay

Chesapeake Bay
(Photo : wikicommons) Scientists now know why the bottom of the Chesapeake by is so much saltier than the rest.

*This story was updated to reflect a change.

Scientists discovered ancient seawater in the Chesapeake Bay estimated to be 100 to 145 million years old, National Geographic reported.

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The water was around 1.1 miles deep and preserved by a 56-mile wide crater formed 35 million years ago when an asteroid landed in the bay. On its way to the bottom, the space rock spurred tsunamis that may have spread to the Blue Ridge Mountains, 100 miles of sea away.

"The water was in the sediment long before the impact occurred. The impact simply reshuffled the sediment in large blocks, which helped preserve it," study leader Ward Sanford, a hydrologist with the U.S. Geological Survey, told Nat Geo.

Now in a hole about 60 square miles, the crater is the size of a large lake. Scientists started drilling for samples back in 2005, but it took several more years to measure age, according to Nat Geo. The results of the samples and analysis were published Nov. 13 in the journal, Nature.

The Chesapeake Bay, which spans Virginia and Maryland, is an estuary (the largest in the country), meaning it's connected to the sea but surrounded by enough land and connected to enough rivers so that its water has a brackish quality, or something between salt and fresh water. Thus, Sanford and his team first had to determine where the water came from -- by sea or river. That process was relatively straightforward, unlike determining its age. Eventually, they devised a method comparing helium levels in the crater to the helium levels of the surrounding area, according to Nat Geo.

The discovery answered at least one question surrounding the Chesapeake Bay. Scientists didn't really know why samples deep water samples always had such high salt content, Nat Geo reported. They can now attribute that quality to the asteroid that hit 35 million years ago. In its descent, the giant rock locked up a large portion of the Atlantic Ocean deep below the bay's surface. 

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