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300 MILLION BCE

A Leaf Transformed into Coal

Before there were three rivers, there was an ocean. Before the Monongahela, the Allegheny, and the Ohio, what-would-be Pittsburgh was on the east coast of a long-forgotten continent named Laurasia. By the late Paleozoic, some 300 million years ago, the ocean between Laurasia and the supercontinent Gondwana narrowed, so that the tectonic plates between primordial North America and future Europe pushed up a jagged spine of mountains, peaks that erosion would one day winnow into the pleasant green roll of the Alleghenies and the Appalachians. However, during the Carboniferous Period (named for our most lucrative resource), Pittsburgh was on the edge of a shallow, temperate sea that stretched across the flat basin of the Midwest.

If you could stroll along the silty beaches of Pittsburgh during the close of what geologists call the Pennsylvanian Period, you’d find yourself in the tropics. Temperatures were humid and damp, and the atmosphere was 35 percent oxygen (more than twice as much as today). Across the swampy environs traipsed a number of different creatures: mollusks, bivalve crustaceans, and the ancestors of clams that lined the rocks in the shallow coves of Pittsburgh. Many-tentacled cephalopods and freshwater sharks patrolled the marshes of the Commonwealth, and though decreasing in numbers as they slid toward extinction, the shiny hard bodies of trilobites accumulated in the ponds, creeks, streams, and mangroves. Pleasant-looking Fedexia, a two-foot long amphibian appearing like a large salamander, made her home here, and Hynerpeton would have waddled from the water to the land with her stubby, amphibious legs while she smiled her broad, froggish grin.

A novel occurrence upon the land, as the earliest reptiles began laying amniotic eggs, their speckled, hard shells making it possible to give birth outside of the water. And because of the oxygen-rich air, which allowed them to more efficiently respirate, arthropods and insects were able to reach gargantuan proportions, including the grotesque Arthropleura, centipedes that grew longer than six feet, with smooth eyeballs the size of softballs. They were joined by Meganeura, dragonflies that had twice the wingspan of a dove. As the biochemist Nick Lane soberly remarks in Oxygen: The Molecule that Made the World, “Gigantism was unusually common in the Carboniferous.” During this period there were spiders with two-foot long legs, scorpions three feet long, and newts that reached dimensions of an astounding sixteen feet. Arthropleura’s perambulations and Meganeura’s swoops, light refracted through the gossamer fabric of her rainbow wings, remind us of the inviolate wisdom of paleogeography, paleontology, and geology—this land is ours, but only for a bit.

Over the eons, silty beaches pressed into sandstone, and further west, the preserved bodies of millions of corals transformed into green limestone, a rich vein to be tapped by miners. Thick-branched, green-palmed fronds reached out of the sun-dappled mangroves that covered Allegheny County, and when they died and fell into the shallow, tepid water, the lack of wood-consuming bacteria (which hadn’t evolved yet) ensured that these fibrous plants wouldn’t decompose. Instead, they sank into the silty soil like eternal, beautiful corpses, petrifying into statues. In the rock there is evidence of the sublimity of deep history, the foreign country which composes the epochs—palms converted to peat, and peat transformed into rock. From those dead trees, there was a symphony of compression that molded them into black carbon, the bituminous that threads in a vein across the ocean from Canonsburg, Washington County, to Cardiff, Wales.

Mt. Washington, overlooking the skyline of Pittsburgh from the southern bank of the Monongahela, was not there 300 million years ago, but the pressed remains of fern and Fedexia have long been entombed there as hard anthracite. Before it was called “Mt. Washington,” it was named “Coal Hill” by the English settlers at the forks of the Ohio who noted the rock’s presence because the well water was as dusky as it was in Wales and Cornwall. When the first mining operation opened there in 1762, coal was cut from the side of the rock face and transported on horseback into the settlement where it heated winter rooms. By the late nineteenth century, over thirteen million tons of coal were excavated annually. Lane writes that “Coal that was buried in the Carboniferous, and is today dug out and burnt, was nonetheless buried for 300 million years. Its burial helped raise atmospheric oxygen levels throughout this time, just as burning it is lowering them again today.”

Arthropleura and Meganeura thus have their revenge; their cremation pushing carbon dioxide in our atmosphere up toward untenable levels. Call it a geological irony, as the long-dead remains of creatures we can scarcely imagine facilitate an extinction of our own doing. We transformed their bodies into energy, but they finally made their mortality our own. In What is Life?, evolutionary theorist Lynn Margulis wrote that “Life today is autopoietic … planetary in scale. A chemical transmutation of sunlight, it exuberantly tries to spread, to outgrow itself…. Life transforms itself to meet the contingencies of its changing environment and in doing so changes that environment.” Both explanation and cracked hope in that, for life shall ever remain, even if we don’t.

British geologist Jan Zalasiewicz, in his poetic The Planet in a Pebble: A Journey into Earth’s Deep History, ruminates on an individual rock, writing that its “stories are gigantic, and reach realms well beyond human experience, even beyond human imagination.” A pebble extends “back to the Earth’s formation…. Something of the Earth’s future, too, may be glimpsed beneath its smooth contours. Battle, murder, and sudden death are there, and ages of serenity too.” So it is with a pebble that you might come across while hiking the orange and red thicket of Frick Park on a crisp autumnal day, some small shard of earth having been here in Pittsburgh millions of years before, a resident over the millennia, mute witness to when Pennsylvania glaciers encroached just north of the city, to when this place was on the coast upon a silty beach, to when it was under the ocean. Epics of epochs. Stanzas of strata. There is a lyricism to minerology and a poetics of geology from the distant past to the far future. People die, but pebbles remain.

Geologists have taken to calling our own epoch the “Anthropocene,” the age when humanity makes its mark on the world. But in some sense it’s an aftershock of the Pennsylvanian, casting its coal upon the ever-warming water from some 300 million years in the deep past. If geology is but poetry in rock, what stanza do we contribute? Perhaps 300 million years hence, there will be just a few centimeters, maybe a foot, of rock shot through with steel, reinforced concrete, and plastic, testifying to the reality that we once existed.