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Bay Blog: geology


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.

Image courtesy Nicolle Rager-Fuller/National Science Foundation

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.

Learn more.


BayBlog Question of the Week: How was the Chesapeake Bay formed?

Welcome to the second installment of our newest feature, the BayBlog Question of the Week. Each week we'll take a question submitted through the Chesapeake Bay Program website and answer it here for all to read.

This week's question comes from Samantha. She asked:

What forces of nature caused the Chesapeake Bay to form?

The Chesapeake Bay as we know it today took on its current shape about 3,000 years ago, but its geologic history can be traced back about 35 million years. Around this time, a rare bolide, or a comet-like object from space, impacted the Earth. This impact did not create the Bay, but it did contribute to natural processes that eventually formed the Bay as we see it today.

The bolide collided with the Earth near what we now call Cape Charles, Virginia, on the lower tip of the Delmarva Peninsula, and created a crater. The crater is thought to have been as large as Rhode Island and as deep as the Grand Canyon. According to this article from National Geographic News, the impact of the bolide led to tsunamis and the decimation of marine life in the surrounding areas. The crater lay beneath sand, silt and clay for millions of years before it was discovered.

It was about 18,000 years ago when the Bay really began to form, as glaciers from the last Ice Age began to melt. During this time period, mile-thick glaciers existed as far south as Pennsylvania and the Atlantic coastline at that time reached about 180 miles farther east than it does today. As the glaciers melted, they carved rivers and streams flowing toward the coast and sea level rose continually. This led to the eventual submersion of what we know now as the Susquehanna River Valley.

History is rich in the Chesapeake Bay; evidence of the ancient Susquehanna River can still be found in a few deep troughs that form a channel along a large portion of the Bay’s bottom. But the Chesapeake’s 3,000 year history in its present shape does not mean there haven’t been changes. In fact, the Bay is constantly changing due to the forces of erosion and sediment transport.

For more information about the history of the Chesapeake Bay, visit our Bay History  page.

Do you have a question about the Chesapeake Bay? Please send it to us through our web comment form. Your question might be chosen for our next BayBlog Question of the Week!

Keywords: questions, geology
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