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Throughout the history of life, different organisms have appeared, flourished and become extinct.
Many of these organisms have left their remains as fossils in sedimentary rocks.
a fjord created by a glacier Source: National Park Service, Those Fabulous Fjords!
The shape of the modern Chesapeake Bay was formed through a combination of both erosion by the Susquehanna River and deposition by ocean currents.
The Chesapeake Bay fills the drowned valleys of the Susquehanna and James rivers, plus tributaries that intersected the Susquehanna.
The current shape of the bay is less that 10,000 years old - so Native Americans arrived in in Virginia in time to witness the conversion of multiple freshwater river channels into the brackish estuary of the modern Chesapeake Bay.
Some of the most useful fossils for dating purposes are very small ones.
For example, microscopic dinoflagellates have been studied and dated in great detail around the world.
Over the last 500,000 years, the Delmarva peninsula has grown towards the south, fed by sediments eroded off the Appalachian Mountains in Pennsylvania/New York and carried by ocean currents.Different species of ammonites lived at different times within the Mesozoic, so identifying a fossil species can help narrow down when a rock was formed.Correlation can involve matching an undated rock with a dated one at another location.Chesapeake Bay bathymetry Source: National Oceanic and Atmospheric Administration (NOAA) National Geophysical Data Center The bay is a feature on the Coastal Plain.The Coastal Plain east of I-95 was created over the last 150-200 million years by erosion from the Appalachian Mountains and by deposition of sediments at the bottom of the Atlantic Ocean.