The period of ancient life called the Paleozoic Era began about 500 million years ago and came to an end about 200 million years ago. Great changes in life took place throughout this era.
During this 300 million years many changes occurred, with a progression from the Age of Invertebrates to the Age of Fishes and the Age of Amphibians. During this era came the first vertebrates, land animals, insects, plants, forests, and seed-bearing plants.
The Paleozoic Era also saw a variety of climates. During long periods of warm dry temperatures, great deposits of salt were formed. There were also periods of warm humid climate in which vast coal-forming swamps came into existence. There were periods of very cold climate when huge glaciers covered the earth.
There were seven recognized periods that made up the Paleozoic Era. They are named after places where rocks of the period were first studied. Listed in order of occurrence they are: Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian. European writers refer to the Mississippian and Pennsylvanian periods together as the Carboniferous, or coal-forming, Period. The Appalachian revolution took place during the Paleozoic Era and resulted in the creation of the Appalachian Mountains near the close of the era.
There were many changes geographically during this period of ancient history. Large inland seas were formed when rising ocean waters flooded interior areas of North America. At other times uplifting occurred, the seas receded, and mountains may have been formed. These inland seas of the seven periods of the Paleozoic Era differed considerably in extent and location. There was no regular pattern or sequence to their origin and disappearance. Some existed for very long periods of time, while others were of shorter duration. Some formed at the start of periods, others in the middle or at the end. The three largest inland seas occupied broad shallow depressions known as the Appalachian Trough, the Cordilleran Trough, and the Ouachita Trough. The Appalachian Trough was located roughly where the Appalachian Mountain chain is today. The Cordilleran Trough occupied the Rocky Mountain area of today. The Ouachita Trough stretched from across Oklahoma to Texas and New Mexico.
This was an era of many changes. There were many beginnings, evolutional processes, and endings during the era known as the Paleozoic Era.
