Carboniferous Period (359 to 299 million years ago)
The Carboniferous Period got its name from the abundance of coal deposits in rocks of Late Paleozoic age in Europe. In the United States, the Carboniferous Period is subdivided into the Mississippian Period and Pennsylvanian Period. An abundance of coal deposits of these ages also exist in eastern and central United States. During the Carboniferous the world was very different than today. The Earth's atmosphere was much thicker, having as much as 40% more oxygen and a more uniform global environment than exists today by some estimates.