When studying coal formation, origins usually point to the Carboniferous period in geologic history, 359-299 million years ago. Shallow inland seas, like the Western Interior Seaway discussed in the last post, were intermixed with thick trees and plant life, creating the perfect swampy wetlands where coal is formed. Decaying plant matter, buried and squeezed by mud, retains a lot of carbon. Over millions of years, the layers of dead plants undergo a process of pressure called carbonization.
The deeper the burial, the better the coal; higher carbon concentrations in the rock burn better and cleaner. Carbonization creates four main types of coal, from lowest to highest grade: lignite, sub-bituminous, bituminous, and anthracite.
Coal is formed on all continents, and the U.S. is among the biggest sources. While most U.S. coal comes from the East Coast, most famously from Pennsylvania and the Appalachian Region, a significant amount comes from the ‘Western Coal Region’, essentially the Great Plains. Coal from the western United States tends to be Cretaceous in age (see the post The Cretaceous Interior Seaway), corresponding with the dinosaurs, and more importantly the Western Interior Seaway, which provided the wet environment and flourishing plant life needed to form coal.
“Coal is the largest source of energy for generating electricity in the world, and the most abundant fossil fuel in the United States.”
Nine major coal-producing regions exist within the Great Plains, including some resources in Canada, and Wyoming is by far the top producer. The majority of these locations produce low-grade coal, of the lignite and sub-bituminous types. These sources supplied early explorers, farmers, and railroads, but after World War II, mining and production of coal took a nose dive. The need for energy did not decrease. In fact, it exploded, and desire for fuel has only increased since the 60s. The government also began setting stricter emissions standards at this time, and as a result, many hopeful surveyors set out to find their fortune in clean-burning coal.
Featured image courtesy of U.S. National Archive:
See the following sources for more info:
Roberts, Laura N. Robinson, Laura N. Robinson. Kirschbaum, Kirschbaum, Mark A., and Geological Survey, Issuing Body. Paleogeography of the Late Cretaceous of the Western Interior of Middle North America: Coal Distribution and Sediment Accumulation. U.S. Geological Survey Professional Paper; 1561. Washington: Denver, CO: U.S. G.P.O.; U.S. Geological Survey, Information Services, 1995.