When inventors perfected the steam engine, every industry quickly transitioned to the new mechanism. Production lines, roads, waterways, and railways harnessed the power of boiling water to spread across the land. However, it was thanks to the glossy black coal seams that society could develop to contemporary heights.
This carbon-rich rock also accelerated the pace of climate change, but the role of coal in the Industrial Revolution cannot be understated. According to paleobotanist Bill DiMichele from the Smithsonian Institution, “coal is king,” and this remains true in some regions.
Even as renewable energy gradually stabilizes, the United States in 2020 still saw 20% of its electricity generated by coal-fired power plants. “At this point, coal is still very important,” asserted expert DiMichele.
“Coal formation” is not a specific type of coal, but this term refers to the oxidation of material in coal that creates a shimmering appearance. Soon after exposure, the air will oxidize all the material causing the shimmer.
Fortunately, humanity can thrive on the same planet with this precious resource. Hundreds of millions of years ago, in dense swampy areas on primordial continents, a series of climatic events and continental shifts helped bury a massive amount of vegetation. When pressure, temperature, and time were added to the equation, the plant matter transformed into peat, and then hardened into coal.
The process of coal formation requires a precise combination of conditions in a specific order. How could such a coincidence occur?
When geologists began classifying strata, the Carboniferous Period (approximately 300 to 360 million years ago) was one of the first named periods. This era also witnessed vigorous plant growth on land. The term “carboniferous”, meaning “coal-producing” in Latin, accurately describes the nature of the sedimentary layers containing most of the coal in Great Britain.
However, thousands of years after the Carboniferous Period, coal formation continued in other regions, sometimes on an even larger scale. Paleobotanist Kevin Boyce explains that “coal doesn’t stop [forming]; it just moves to other areas.” According to his data, the vast coal seams of Siberia, China, and Australia date back to the Permian Period, which follows the Carboniferous. Some survey parameters suggest that coal formation during the Permian was even more vigorous than the “coal-producing” period.
Illustration of Carboniferous swamps.
Nevertheless, coal does not form at a steady rate. Throughout Earth’s geological history, the formation of large coal deposits has been interspersed with smaller formation periods. This inconsistency raises the question: why hasn’t the coal formation process been consistent throughout Earth’s history?
In the past, there was an explanation that the Carboniferous Period produced a lot of coal because woody plants had just started to develop, and fungi had not yet evolved enough to decompose lignin, the polymer that gives wood its hardness. As a result, ancient plants did not disappear but were preserved under layers of sediment and eventually turned into coal.
This explanation is reasonable in many respects, but it has not convinced the entire expert community. First, the likelihood of fungi not synthesizing lignin-decomposing enzymes after tens of millions of years is very low. Furthermore, coal does not only come from woody plants. In many areas, the majority of buried vegetation in sediments consists of large plants related to clubmosses (also known as “stone pines”) today, which contain very little lignin.
A precise formula is needed for Earth’s alchemists to produce coal
In a scientific report published in 2016, researchers Boyce, DiMichele, and their colleagues refuted the above hypothesis, arguing that the Carboniferous Period simply gathered all the necessary geological factors; not to mention other coal-forming periods.
Across various lands, the components supporting coal generation are abundant. According to Boyce, all that is needed is ample rainfall (to help trees grow and form swamps) and a large basin (to hold the trees) for coal to potentially form over time.
In waterlogged swamps, peat will form.
During the Carboniferous Period, as the continents moved closer together to form Pangaea, the collisions between tectonic plates created mountain ranges and large basins. These were potential coal basins. Some of these basins, present in Europe today and the eastern United States, emerged under tropical humid conditions.
Essentially, the process of coal formation depends on the number of large basins located in areas that meet the necessary conditions, allowing organic matter to accumulate in large quantities.
When plants died in these waterlogged areas, many trees fell into stagnant ponds with low oxygen content. Since most decomposing organisms (like bacteria, fungi, etc.) cannot thrive in such harsh environments, the plants do not have the opportunity to decompose. Instead, they decay into peat. Even so, peat cannot become coal unless the land gradually dries out and the peat disappears. A preservative sediment layer must cover it, allowing the coal formation process to begin.
Sometimes, in swamps near the sea or coastal areas frequently exposed to tidal surges, peat basins often exist. This phenomenon often occurs during Earth’s glacial periods.
Glacier in Argentina.
Peat forms during freezing periods, when polar ice thickens and sea levels drop. And when the ice melts, water brings sediments to cover the peat basin, burying the decayed plant matter that will eventually become coal. In some archaeological areas, stone records depict alternating layers of terrestrial and marine sediments. Deep inland, eroded soil can also cover peat basins and yield similar results.
Continuing for cycles lasting thousands of years, new layers of sediment and peat compress the old ones. The immense weight squeezes out water from the peat, causing the peat to harden over time. Lignite gradually forms and then eventually transforms into coal.
A coincidence spanning eons is unique
The reason coal is abundant during the eponymous period is more complex than we think; it is not just a matter of waiting for fungi to evolve the ability to decompose wood. However, researcher DiMichele thinks simply about the natural process with the involvement of three factors: glacial periods, heavy rainfall, and sediment layers.
As long as the basin is in the right place, the coal formation process can occur steadily. “Once you see the system connecting, it’s not that complicated,” he says. “Glaciers come and go. Peat forms and doesn’t form at the same time. It makes sense.”
Coal appears in many places around the world.
Additionally, coal appears in numerous locations around the world. Even today, some tropical regions like Borneo in Asia or the forests in the Congo Basin are accumulating peat with the hope of becoming future coal seams.
However, truly, no processes in modern or contemporary history can compare with the Carboniferous and Permian periods. To create the vast fossil fuel treasures that led to the Industrial Revolution, a precise sequence of events was necessary, and Earth was not always ready.
