The Geosphere/Lithosphere is all the land we walk on, the mountains we climb and the layers of the Earth beneath our feet, right down to the Earth’s core. Plate tectonics, volcanoes and other processes that cause the land to move all help to shape the geosphere.
The Chesapeake Bay itself has been changing continuously for thousands of years. Some changes are sudden, whereas others take place over such a long period of time and can only be seen by looking back into geologic history.
About 35 million years ago, a rare bolide – a comet- or asteroid-like object from space – hit the area that is now the lower tip of the Delmarva Peninsula, near Cape Charles, Virginia, forever changing landscape around the impact area. The bolide created what geologists call the “Exmore Crater,” which is believed to be as large as Rhode Island and as deep as the Grand Canyon. Although this bolide did not create the Chesapeake Bay, it helped determine that a bay would eventually be located there.
Approximately 18,000 years ago, the glaciers began to melt, carving streams and rivers that flowed toward the coast. As the glaciers melted, sea levels rose, eventually submerging the area now known as the Susquehanna River Valley and eventually creating the Bay as a result.
To fully define the Bay ecosystem, we must go far beyond its shores. Although the Bay itself lies entirely within the Atlantic Coastal Plain, its watershed includes parts of the Piedmont Plateau and Appalachian Province.
Atlantic Coastal Plain
The Atlantic Coastal Plain is a flat, lowland area with a maximum elevation of 300 feet. The coastal plain is supported by a bed of rock covered with southeasterly sloping wedge-shaped layers of sand, clay and gravel. Water passing through this loosely compacted mixture dissolves many of the minerals it comes into contact with - the most soluble elements being iron, calcium and magnesium. The coastal plain extends from the continental shelf to a fall line located west of the Bay. Waterfalls and rapids clearly mark the line, which is close to Interstate 95. Cities like Baltimore, Maryland, Washington, D.C. and Richmond, Virginia were built along the fall line to take advantage of potential water power generated by the falls. Because of this, these cities became commerce hubs as colonial ships could not sail past the fall line and had to stop to transfer their cargo to canals or overland shipping.
The Piedmont Plateau ranges from the fall line westward to the Appalachian Mountains. This area is divided by Parrs Ridge, which stretches across Carroll, Howard and Montgomery counties in Maryland and adjacent counties in Pennsylvania. Several types of dense crystalline rock, including slates, schist, marble and granite compose the eastern side of the ridge. This geologic variety creates a very diverse landscape. The western side of the Piedmont consists of sandstones, shales and siltstones layered over by limestone. Waters from the western side of the ridge flow into the Potomac River
The Appalachian Province lies in the northwestern parts of the watershed. These areas are characterized by mountains and valleys, and are rich in coal and natural gas. Sandstone, siltstone, shale and limestone form the bedrock. Most of the water from the Appalachian Province flows into the Bay from the Susquehanna River.