When you think of the vast expanse of wet prairies in Florida’s Everglades, the peat-filled wetlands of Georgia’s Okefenokee Swamp, or the Amazon River Delta, coal isn’t the first thing that comes to mind. But these landscapes are modern-day examples of the enormous, ancient inland seas and dense tropical swamps that turned into today’s coal beds. Much of the world’s coal dates back to the Carboniferous Period, some 318 million years ago, and contains plant matter and fossils from before the era of the dinosaurs.
Coal is America’s mighty rock. Because coal burns at a slow rate for a long time, it’s more efficient as an energy source than other fossil fuels. And the United States is naturally well-endowed with coal resources—25 percent of the world’s coal reserves are within our borders. Coal has been the leading electricity source worldwide, and over the past 10 years it has supplied one-half of the increase in global energy demand, growing even faster than renewables. And now it’s one of the most fiercely disputed fuels.
There is a dark side to coal. It produces more carbon dioxide when burned than other fossil fuels do and adds disproportionately to global climate change. Ecological costs are abundant, too, and range from mountain-top removal mining to air pollution to coal ash spills.
Coal exports from the United States this year are expected to reach 125 million tons, breaking the previous record of 113 million tons set in 1981. And according to the World Energy Council, the world’s coal use is expected to rise 60 percent by 2030, with developing countries responsible for 97 percent of this increase.
To understand the conflicts surrounding coal, it helps to step back and review how we came to have this contested resource. The two main ingredients in the recipe for coal are peat and time. Decayed plant matter and sediment accumulated in large basins in the Earth’s crust to form peat. Over millions of years, layers of mushy peat accumulated in geologic basins and were buried by sediment that accumulated little by little, from stormwater runoff or the wind, for instance. Over time, the basin of sediment sank below the Earth’s surface.
Depending on tectonic forces, such as the stability of the earth’s crust in the area or an uplift in mountain ranges, the peat deposits ended up deep underground or closer to the surface. As the buried sediment compacted under pressure, water was squeezed from the peat, natural heat from the earth’s core baked it, and coal formed, a process called coalification.
Peter Warwick of the U.S. Geological Survey says coalificaiton is like the cartoon image of Superman squeezing a chunk of coal to make a diamond. “It’s the same concept. You need to compact and squeeze this peat to form coal,” he said; coal is just “concentrated carbon.”
The United States had three major coal-forming periods: the Pennsylvanian (318-299 million years ago), which formed the Appalachian coal beds; the Cretaceous (145-65 million years ago), which formed coal in Colorado, Utah, and New Mexico; and the early Tertiary (65-35 million years ago), which led to major coal deposits in Wyoming, Montana, North Dakota, and Texas.