FOSSILS ET AL.
When the Earth Was Fed Up With Life: The End-Permian Mass Extinction
The most devastating mass extinction the Earth ever faced
The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.
— Carl Sagan
The above quote by Carl Sagan, the greatest science popularizer, describes the incredible importance of Earth for life. In many cultures worldwide, Nature has been given the title of ‘Mother,’ signifying that it gives us everything, doesn’t demand anything in return, and is crucial for birth. And for a large part of Earth’s history, that has been the case, except for the mass extinction events observed by fossil records across the globe. A mass extinction is most commonly defined as an event in history when at least half of the species on Earth go extinct within a million years. The Big Five mass extinctions, as they are known, have been time periods in which life has suffered the most, and these are:
- The End-Ordovician Mass Extinction
- The Late Devonian Mass Extinction
- The End-Permian Mass Extinction
- The End-Triassic Mass Extinction
- The End-Cretaceous Mass Extinction
The star of the show
The most devastating of these is supposed to be the End-Permian mass extinction, which happened around 252 million years ago (which is sneaky because it sounds the least dangerous). What makes this event the most ferocious of all is the time scale in which it happened. As a reference, if we assume Earth's entire history to be a day long, the Permian mass extinction happened in a second! That’s it; all it took was a second (or 60k years) to wipe out more than 90 percent of the species on Earth. This was way faster than, for example, the Late Devonian mass extinction, which took around 15–20 million years. There is still a lot of debate over the cause of this extinction, and various scientists have put forward various theories in that regard.
Traces of a murder
But, to begin with, how do paleontologists figure out a mass extinction? They study the rock layers in the Earth’s crust to identify changes in fossils and then use isotopic dating techniques to age the layers of the rocks. Then, they also studied the fossil record before and after the probable time of extinction and checked how many species disappeared from the fossil record. In this case, chert also hinted at a possible mass extinction. Chert is a sedimentary rock whose primary component is silica. It is deposited on the sea floor when plankton in the seas absorb dissolved silica and die later. A lack of this chert, called chert gap, hinted at the insufficient number of sea organisms that may have stopped reproducing and, therefore, producing chert.
Another fossil record that strengthened the possibility of a mass extinction was the absence of coal deposits for about 10 million years during the late Permian. This called the coal gap, indicated that there was not much plant life in the world to contribute to the coal reserves. Then there is another slightly creepy and unconfirmed evidence that rivers at that time stopped their meandered flow because there were no trees left to divert the flow of rivers.
Life, just before death
The later part of the Permian period flourished with land and water life. At this time, all the continents of the Earth were combined into one supercontinent, called Pangaea, meaning ‘all of the land’. The land-dwelling therapsids and pelycosaurs have stolen all the limelight. Therapsids were the clade of animals from which mammals evolved. These included animals like the scary Inostrancevia, about 11 feet long. They were the rulers of the land; they hunted and ate whatever they liked. Then there was the Lystrosaurus, a pig-sized herbivorous animal. Dimetrodon were a species of pelycosaurs that were the dominant predators before Inostrancevia. I can best describe dimetrodons as lizards with sails on their backs. Most of these creatures were wiped out during the extinction.
The Permian Sea hosted Brachiopods, Ammonoids, Conodonts (which looked like aliens’ pet fish), Ichthyosaurs, and plankton, among other creatures. The conodonts and ichthyosaurs would survive this mass extinction only to be completely washed away during the end-Triassic mass extinction.
The suspects
What caused this mass extinction is still highly debated, and over the years, many convincing theories have been put forward after extensive study of this mass extinction.
The Siberian Traps — The Siberian Traps were a series of active volcanoes spanning over 2 million square kilometers in present-day Siberia. The eruption of these volcanoes is supposed to have covered miles and miles of land in thick lava. The greenhouse gases released in these eruptions are thought to have started warming the planet. The degree of this event can be understood by the fact that at present, about 40 gigatons of carbon dioxide are released into the atmosphere and water every year, while it is estimated that during this mass extinction, somewhere between 10,000 to 5,0000 gigatons were released. The current CO2 concentration in the atmosphere is 420 ppm. At the same time, according to some scientists, it may have reached 20 times that number during the end of Permian, and as a result, global temperatures shot up by more than 35 degrees Celsius.
As if the gases emitted by the volcanoes weren’t enough, the lava seeped into the Earth, igniting the coal reserves and releasing more greenhouse gases. These increased CO2 levels in the atmosphere caused the ocean water to lose oxygen, as in high temperatures water loses its ability to hold onto dissolved oxygen. Acid rains may also have killed a lot of plant life. Mercury, which is a toxic metal, was also released by the volcanoes, as was evident by the mutagenesis (genetic mutation) in surviving plants.
Rotten eggs — Or maybe something that smells like rotten eggs. Hydrogen sulfide, which is a gas at room temperature, is a highly poisonous gas. I distinctly remember its pungent smell during my high school lab experiment. At a concentration of 700 ppm, it can instantly kill a human. Scientists have discovered that along with the anoxic (less oxygen) conditions induced by high levels of carbon dioxide, there was a good amount of isorenieratene deposit at the time of the mass extinction. This is a compound produced by green sulfur bacteria that grows in anoxic conditions and requires hydrogen sulfide gas. Also, the abundance of fool’s gold (iron sulfide) attests to the presence of this toxic gas. Whether the levels of hydrogen sulfide were enough to choke terrestrial and aquatic life is debatable.
Ozone depletion—Ozone depletion is theorized to be another reason for this mass extinction. Researchers who studied the pollen fossil during the late Permian period indicate that some deformities arose from the pollen being exposed to UV light, which was supposed to be a result of the thinning of the ozone layer in the atmosphere. The cause of this depletion is supposed to be methyl bromide gas released during the volcanic eruption.
Methanogens — In a research paper titled “Methanogenic burst in the end-Permian carbon cycle,” the researchers argued that certain anaerobic microbes had acquired the pathways to create methane from acetate (a carbon compound), thus using increased carbon levels to survive. Their numbers grew rapidly, and so did the volume of methane, which is more dangerous than carbon dioxide as a greenhouse gas. This methane then increased the global temperatures, leading to the eventual extinction of life.
There are other less popular theories, like asteroid impact and interstellar dust, but scientists have debunked them.
The aftermath
Whatever the reason or group of reasons, one thing is clear: nature did not go easy on life on this planet for these 60000 years. Because it had such a bloodbath in such a short period, the Permian mass extinction is also known as the Great Dying. Life was hit so hard that it took another 10 million years to make a comeback, but it did, as it always has. The Earth cooled down in the aftermath of this mass extinction, and the first dinosaurs appeared. However, they were not as glorious and big as during the Cretaceous period and would have to live alongside mammals before becoming the absolute rulers of the planet.
I believe this mass extinction should be included in school textbooks to teach young kids about the hazards of exploiting the Earth’s resources and the impending dangers if sustainable development goals are unmet. The world once came together in Montreal to reverse the ozone hole by limiting the production and use of ozone-depleting substances; we can also save the planet from global warming.
Published in Fossils et al. Follow to learn more about Paleontology.
