Much of south-central Pennsylvania’s landscape is extremely ancient. For instance, a large swath of Cumberland County, where this photo was taken, straddles the Cambrian, Ordovician, and Silurian Ages, dating from 570 million to 417 million years ago. Limestone was one of the major types of soil generated in these millennia. There was also a mass extinction in these times that spanned from 445 to 440 million years ago – some estimates argue that it was two times as severe as the K-T extinction event that ended the age of the dinosaurs!
