The Susquehanna River cuts through the folds of the Valley-and-Ridge province of the Appalachian Mountains in this photograph taken by the crew of the International Space Station.
The Valley-and-Ridge province is a section of the larger Appalachian Mountain Belt between the Appalachian Plateau and the Blue Ridge physiographic provinces. The northeast-southwest trending ridges are composed of Early Paleozoic sedimentary rocks. The valleys between them were made of softer rocks (limestone and shales) that were more susceptible to erosion; they are now occupied by farms. The Susquehanna River cuts through several ridges as it flows south.
The Susquehanna River flows 444 mi (714 kilometers) from upstate New York to Maryland, draining into Chesapeake Bay.
Fifty years ago, on April 22, 1970, people around the world marked the first Earth Day. On this Earth Day, as we physically separate ourselves by necessity, we can still collectively appreciate the wondrous beauty of our planet and the extraordinary science that helps us understand how it all works – and we can do it from our homes.
Follow along this week as we celebrate #EarthDayAtHome with NASA.
Image Credit: NASA/Expedition 61; Caption by Laura Phoebus, Jacobs, JETS Contract at NASA-JSC
图片来源：NASA/Expedition 61; Caption by Laura Phoebus, Jacobs, JETS Contract at NASA-JSC