The Bay has been changing continuously from the time it was born, 35 million years ago when a meteor-like object hit the earth and created a giant crater at the southern tip of the Delmarva peninsula. The Exmore Crater was as large as Rhode Island and as deep as the Grand Canyon. Each change thereafter, large and small, has affected the Chesapeake’s ecosystem in curious ways. Sometime quickly and sometimes that can only be measured in geologic time.

It was during the last ice age that glaciers stretched as far south as Pennsylvania. These walls of ice were a mile thick and they scoured the earth underneath leaving scars we can still readily see today, 18,000 years later. At this time, the Atlantic coastline was almost 200 miles farther east than it is today. So much of the earth’s ocean water was tied up in these massive glaciers that the level of the oceans was significantly lower. So as the ice began to melt, streams and rivers flowing toward the coast filled the Susquehanna River Valley.

The Susquehanna River is today a major river stretching from upper New York state, through Pennsylvania, Maryland and emptying at the very top of the Chesapeake. But thousands of years ago, the Susquehanna was much bigger. It filled its entire valley with what can only be call a torrent that lasted for 4 thousand years. As it emptied onto the coastal plain, it carved the Chesapeake Bay as we know it today.

While the average depth of the bay is relatively shallow at 21 feet deep, there are deep troughs which run the length of the Bay that are believed to be evidence of the ancient Susquehanna’s powerful surge. These troughs are used as the major shipping channels for the Bay’s traffic. The Chesapeake has two major shipping ports in Baltimore, Maryland, and in Hampton Roads, Virginia. The cargo ships that travel to and from these cities still, today, travel the paths of the ancient river.

To appreciate how truly unique the ecosystem of the Chesapeake is, it must be remembered that while the Bay lies entirely within the Atlantic Coastal Plain, its watershed includes parts of the Piedmont and Appalachian ranges. The feeder streams and rivers that flow into the Bay have different chemical identities depending on the geology of where they originate.

The Atlantic coastal plain is a flat lowland area supported on a bed of crystalline rock covered with layers of clay, sand and gravel. Water passing through this loosely compacted mix dissolves many of the minerals. Elements like iron, calcium and magnesium flow into the bay from the Easters Shore.

From the northwest Appalachian region, the bay receives sandstone, siltstone, shale and limestone. Most of the water from this province flows into the Bay from the Susquehanna River.

From the west, the Piedmont region, the bay gets its “hard water” from the calcium and magnesium flowing into the Bay with the Potomac River.

So what all this means is that the Chesapeake is a soup of different chemicals changing constantly. Parts of the bay are different that others. Salt content is one example. The lower bay is much more salty than the upper bay… as are the rivers less salty farther inland versus near the bay tidal waters. This soup, although constantly changing, makes the Bay one of the most unique breeding grounds in the world. It lures a special variety of creatures which make their home here which in turn lures people to live and work here.

The Chesapeake is a magnet. It can be appreciated in so many ways. Even by its unique chemical make-up.

For more articles about the Chesapeake by this author, see: The Chesapeake , The Loon, Bottlenose Dolphin, Bufflehead, Sea Nettle, Barnacle, Blue Crab, Oyster, Eagle