The Prehistoric Earth

IF WE’D BEEN standing in this same spot 252 million years ago, during a slice of time geologists call the Permian period, our surroundings would have been barely recognizable. No factories or other signs of people. No birds in the sky or mice scurrying at our feet, no flowery shurbs to scratch us up our mosquitoes to feed on our cuts. All those things would have evolve later. We still would have been sweating, though, because it was hot and unbearably humid, probably more insufferable than Miami in the middle of the summer. Raging rivers would’ve been draining the Holy Cross Mountains, which were actually proper mountains back then, with sharp snowy peaks jutting tens of thousands of feet into the clouds. The rivers wound their way through vast forests of conifer trees- early relatives of today’s pines and junipers- emptying into a big basin flanking the hills, dotted with lakes that swelled in the rainy season but dried out when the monsoons ended. These lakes were the lifeblood of the local ecosystem, watering holes that provided an oasis from the harsh heat and wind. All sorts of animals flocked to them, but they weren’t animals we would know. There were slimy salamanders bigger than dogs, loitering the water’s edge and occasionally snapping at passing fish. Stocky beasts called pareiasaurus waddled around all fours, their knobby skin, front-heavy build, and general brutish appearance making them seem like a mad reptilan offensive lineman. Fat little things called dicynodonts rummaged around in the muck like pigs, using their sharp tusks to pry up tasty roots. Lording over it all were all gorgonopsians, bear-size monsters who reigned at the top of the food chain, slicing into pareiasaur guts and dicynodont flesh with their saberlike canines. This cast oddballs ruled the world right before the dinosaurs. Then, deep inside, the Earth began to rumble. You wouldn’t have been able to feel it on the surface, at least when it kicked off, right around 252 million years ago. It was happening fifty, maybe even a hundred, miles underground, in the mantle, the middle layer of the crust- mantle-core sandwich of Earth’s structure. The mantle is solid rock that is so hot and under such intense pressure that, over long stretches of geological time, it can flow like extra- viscous Silly Putty. In fact, the mantle has currents just like a river stream. These currents are what drive the conveyor-belt system of plate tectonics, the forces that break the thin outer crust into plates that move relative to each other over time. We wouldn’t have mountains or oceans or a habitable surface without the mantle currents. However, every once in a while, one of thhe currents goes rogue. Hot plumes of liquid rock eventually bursting out through volcanoes. These are called hot spots. They’re rare, but Yellowstone is a example of an active one today. The constant supply of heat from deep Earth is what powers Old Faithful and the other geysters. This same thing was happening at the end of the Permian Period, but on a continent-wide scale. A massive hot spot began to form under Siberia. The streams of liquid rock rushed through the mantle into the crust and flooded out from volcanoes. These weren’t ordinary volcanoes like the one we’re most used to, the cone shaped mounds that sit dormant for decades and then occasionally explode with a bunch of ash and lava, like Mount Saint Helens or Pinatubo. They wouldn’t have erupted with the vigor of those vinegar- and- baking- soda contraptions so many of us made as science fair experiments, No, these volcanoes were nothing more than big cracks in the ground, often miles long, that continuosly belched out lava, year after year, decade after decade, century after century. The eruptions at the end of the Permian lasted for a few hundred thousand years, perhaps a few million. There were a few bigger eruptive bursts and quieter periods of slower flow. All in all, they expelled enough lava to drown sereval million square miles of northern and central Asia. Even today, more than a quarter billion years later, that black basalt rocks that hardened out of this lava cover nearly a million square miles of Siberia, about the same land area as Western Europe. Imagine a continent scorched with lava. It’s the apocalyptic disaster of a bad B movie. Suffice it to say, all of the pariasaurus, dicynodonts, and gorgonopsians living anywhere near the Siberian area code were finished. But it was worse than that. When volcanoes erupt, they don’t expel only lava, but also heat, dust, and noxious gases. Unlike lava, these can effect the entire planet. At the end of the Permian, these were the real agents of doom, and they started a cascade of destruction that would affect millions of years irrevocably change the world in the process.Dust shot in the astmosphere, contaminating the high attitude air currents and spreading across the world, blocking out the sun and preventing plants from photosynthesizing. The once lush conifer forests died out, then the gorgonpsians had no meat. Food chains started to collapse. Some of the dust fell back the atmosphere and combined with water droplets to form acid rain, which exacerbated the worsening situation on the ground. As more plants died, the landscape became barren and unstable, leading to massive erosion as mudslides wiped out entire tracts of rotting forest. This is why the fine mudstones in the Zachelmie quarry, a rock type indicative of calm and peaceful environments, suddenly gave way to coarser boulder strewn rocks so characteristic of fast-moving currents and corrosive storms. Wildfires raged across the scarred land, making it more difficult for plants and animals to survive. But those were just the short term effects, the things that happened within the days, weeks, and months after a particularly large burst of lava spilled through the Siberian fissures. The longer-term effects were even more deadly. Stifling clouds of carbon dioxide were released with the lava. As we know all too well today, carbon dioxide is a potent greenhouse gas, which absorbs radiation in the atmosphere and beams it back down to the surface, warming up the Earth. The CO2 spewed out by the Siberian eruptions didn’t raise the thermostat by a few degrees, it was a runaway greenhouse effect that boiled the planet. But there were other consequences as well. Although a lot of carbon dioxide went into the atmosphere, much of it also dissolved into the ocean. This causes a chain of chemical reactions that makes the ocean water more acidic, a bad thing, particularly for those sea creatures with easily dissolvable shells. It’s why we don’t bathe in vinegar. This chain reaction also draws much more oxygen out of the oceans, another serious problem for anything in or around water. Descriptions of the doom and gloom could go on for pages, but the point is, the end of the Permian was a very bad time to be alive. It was the biggest episode of mass death in the history of our planet. Somewhere around 90 percent of all species disappeared. Paleontologists had a special term for an event like this, when the huge numbers of plants and animals die out all over the world in a short time: a mass extinction. There have been five particularly severe mass extinctions over the past 500 million years. The one 66 million years ago at the end of the Cretaceous period, which wiped out the dinosaurs, is surely the most famous. We’ll get to that one later. As horrible as the end Cretaceous- extinction was, it had nothing on the one at the end of the Permian. The moment of time 252 million years ago, chronicled in the swift change from mudstone to pebbly rock in the Polish quarry, was the closest that life ever came to being completey obliterated. Then things got better. They always do. Life is resilient, and some species are always able to make it through even the worst catastrophes. The volcanoes erupted for a few million years, and then they stopped as the hot spot lost steam. No longer blighted by lava, dust and carbon dioxide, ecosystem were gradually able to stabilize. Plants began to grow again, and they diversified. They provided new food for herbivores, which provided meat for carnivores. Food webs reestablished themselves. It took at least five million years for this recovery to unfold, and when it did, things were better but now very different. The previously dominant gorgonopsians, pareiasaurus, and their kin were never to stalk the lakesides of Poland or anywhere else while the plucky survivors had the whole Earth to themselves. A largely empty world, an uncolonized frontier. The Permian had transitioned into the next interval of geological time, the Triassic, and the things would never be the same. Dinosaurs were about to make their entrance.