Correct Response: C. The coal deposits of the Pennsylvanian Period (also known as the Upper Carboniferous) are sedimentary deposits formed primarily from swamp vegetation. The period lasted from approximately 320 million years ago until 300 million years ago and was a time when equatorial regions were covered in forest swamps of seedless plants. These plants provided most of the carbon for the coal characteristic of the period. The movement of tectonic plates eventually shifted these deposits northward. The remains of microscopic marine organisms (A) are the primary source for the compounds that make up natural gas and petroleum, not coal. Solidification of oil deposits does not produce coal (B), but slow drying out of petroleum deposits can form natural asphalt (also known as bitumen). Lithification of mud (D) produces siltstone, claystone, and shale, but not coal.
