Chesapeake Bay (100-145 Million Years Old): Cape Charles, VA - Oldest Body Of Seawater

Seawater is the salty water found in oceans and seas. It is composed of a mixture of water and dissolved salts, primarily sodium chloride (table salt) along with other minerals and substances. The main difference between a body of seawater and an ocean is size, with oceans being much larger than seas. Seas are also usually located where the ocean meets land and are often partially enclosed by land. 

The oldest body of seawater in America, and the world, is located in Chesapeake Bay. On November 21, 2013  U.S. Geological (USGS) scientists made the discovery while drilling at Cape Charles, Va., to study the Chesapeake Bay Impact Crater site, which is the largest known impact crater in North America.

The body of seawater that was discovered is deposited between layers of sediment deep under present-day Cape Charles, Va. It's high-salinity groundwater. 

USGS scientists have determined that high-salinity groundwater found more than 1,000 meters (0.6 mi.) deep under the Chesapeake Bay is actually remnant water from the Early Cretaceous North Atlantic Sea and is probably 100-145 million years old.

U.S. Geological Survey describes it as the oldest sizable body of seawater to be identified worldwide. National Geographic recognizes it as the oldest body of seawater in the world. The Chesapeake Bay Program describes it as the oldest body of seawater ever identified.

Twice as salty as modern seawater, the ancient seawater was preserved like a prehistoric fly in amber, partly by the aid of the impact of a massive comet or meteorite that struck the area about 35 million years ago, creating Chesapeake Bay. The seawater was isolated, trapped a half-mile underground, and preserved with the help of an asteroid that had smashed into the area around 35 million years ago, creating a huge crater.

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. To determine the origin of the newfound water, the team measured the ratio of two compounds (dissolved chloride and bromide) in the drilling samples. 

This measurement from the drilling samples revealed a clear “fingerprint” of ocean water, according to the study which was published online November 13, 2017 in the journal Nature.

"Previous evidence for temperature and salinity levels of geologic-era oceans around the globe have been estimated indirectly from various types of evidence in deep sediment cores," said Ward Sanford, a USGS research hydrologist and lead author of the investigation. "In contrast, our study identifies ancient seawater that remains in place in its geologic setting, enabling us to provide a direct estimate of its age and salinity."

The watery fossil holds around 3 trillion gallons, and is "the oldest large body of ancient seawater in the world," according to government hydrologists who made the amazing find while mapping the ancient crater under Virginia's Cape Charles. "We weren't looking for ancient seawater," the lead researcher tells the Washington Post, calling the find "surprising."