The Permian Extinction

In a recent entry (“A super-sized bug”), I mentioned that ancient sea scorpions disappeared from the fossil record around 250 million years ago, during a time known as the Permian extinction. What was the Permian extinction? In short, it was one of the most cataclysmic mass extinction events ever to happen to life on earth. There have actually been 5 massive extinctions over the earth’s history. They are the Ordovician extinction (440 million years ago), the Devonian extinction (370 million years ago), the Permian extinction (250 million years ago), the Triassic extinction (210 million years ago) and the Cretaceous extinction (65 million years ago). The Permian was by far the biggest. In total, 70% of all land-based species became extinct; 95% of all marine life was killed. It has been referred to as “the mother of all mass extinctions.”

The Permian period lasted from approximately 286 to 248 million years ago, and was the last period of the Paleozoic era (which lasted from 540 to 248 million years ago). During the Permian period, all of the earth’s continents were in 1 giant land mass. It was called Pangea; shaped like the letter “C,” it spanned the equator. The mouth of the C was a sea called Tethys, while the rest of the world was covered by a giant ocean called Panthalassa.

This configuration of land and ocean led to an expansion and diversification of both terrestrial and marine species. Therapsids were the dominant land-based tetrapod (which means 4-legged creature), and have also been called “mammal-like reptiles.” There were multiple kinds of therapsids, including dinocephalians (a dog-like crocodile), gorgonopsians (a large reptilian saber-toothed tiger), therocephalia (smaller than the gorgonopsians), and dicynodonts (the only herbivores in the group). There were also several primitive turtle-like and reptilian-like creatures, including pareisaurs (armoured herbivores reaching a whopping 9 feet long), procolophonids (chunky lizards with big skulls), and diapsids (which still exist in the form of reptiles and birds). Dominant insects were mostly cockroaches (upwards of 90% of insects were some kind of roach), though dragonflies were also abundant. Terrestrial flora changed dramatically during this time. Pangea had large areas of relatively dry land, as opposed to the damp, jungle-like climate that had existed previously. Swamp-loving trees were replaced with conifers (pine trees), and gingkos, cycads and ferns also become prominent. The marine environment was full of exotic life. Great reefs harbored giant sea scorpions, armoured fish, mollusks, sponges, trilobites, brachiopods (bivalves that look like clams), nautiloids (to which the modern nautilus belongs), and ammonoids (related to octopus and squid).

The organisms of Pangea during the Permian period were vast and varied. But after the Permian extinction, very few of these creatures had survived. What happened to destroy so much of this varied and exotic life? At the moment, there are several theories to explain the massive die-off.

One theory is that massive volcanic eruptions coated the landscape of the present-day Siberian Traps with basalt lava, causing environmental stress, an elevation of the earth’s temperature, and mass extinction. An expansion of this theory says that the increased temperature resulting from the basalt lava would not be enough to destroy so much life. But it could result in the release of methane gas from below the ocean floor, which would further increase global temperatures. Yet another related theory is that the basalt lava decreased the ability of the oceans to dissolve oxygen. Because of this, deep-ocean bacteria thrived (they don’t use oxygen), and they produced massive amounts of hydrogen sulfide. The hydrogen sulfide escaped into the atmosphere, causing acid rain and destroying the ozone layer. In fact, recent evidence from David Bottjer, professor of earth and biological sciences from the University of Southern California, supports this model of an uprising of hydrogen sulfide from the deep ocean. In a paper published in the November issue of the journal Geology, Dr. Bottjer reported evidence that deep-sea organisms were the first to die off, followed only later by creatures dwelling in shallow water. Many people also believe that this model could explain the later Cretaceous extinction event that wiped out the dinosaurs. (That was the second largest extinction event in the world.)

Whatever the cause, the effects on life on earth were nothing short of disastrous. While 70% of land species and 95% of marine species died out during this extinction event, on an individual level, perhaps as many as 99% of all individual organisms died as a result of whatever happened. This clearing of the landscape provided room for the emergence of other well-known species, including the dinosaurs and modern mammals. So in retrospect, it wasn’t a total loss. But it certainly was a tough time for everything involved.