252 million years ago, our planet was journeying from the Permian period into the Triassic period. The boundary between these two large epochs of time is marked by the occurrence of the most severe extinction event known to history. Fondly known as the Great Dying, the Permian extinction event saw to the destruction of 96% of all marine species and 70% of all terrestrial vertebrates (animals with backbones). Not only did all of these species go extinct, but a large amount of Earth’s insect population at the time also died out. Indeed, so many species were lost that the diversity of life on Earth was stunted for another 10 million years.
Scientists have long pondered the cause of the mass extinction. Theories have ranged from mass volcanic action spewing greenhouse gasses into the atmosphere to an impact from an asteroid similar to the extinction of the dinosaurs. However, the dinosaur extinction event is a small change when compared to the Permian extinction event. Now, new evidence is coming to light concerning the cause of this extinction. In a March 2014 study from the journal Proceedings of the National Academy of Sciences, researchers took note that the extinction coincided with the timing of a disruption in the Earth’s carbon cycle.
The researchers, led by Daniel Rothman of the Massachusetts Institute of Technology, had a hunch that the two events may be related, but had trouble reconciling how. Around the time of the extinction, volcanoes in Siberia were erupting at a tremendous rate. Before it was thought that alone, the volcanic activity might account for the large amounts of carbon in the ocean and atmosphere at the time. The volcanic activity did account for some of the extreme rise in atmospheric and oceanic carbon. It also explained the increase in nickel observed in ocean sediments at the time. However, it did not account for all of the massive carbon output, the extreme lack of oxygen in the Permian oceans, or the acidification of the oceans.
Here is where microbes come into play. Researchers believe they have found a culprit that explains all of the symptoms of the Permian extinction in one fell swoop. It is believed now that there was a transfer of genetic material, from a cellulolytic bacterium to a methanogenic archaeon at the time before the Great Dying started. Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic (without oxygen) conditions. This gene transfer allowed this methanogenic bacterium to feast upon the loads of organic carbon in the ocean, a process that resulted in an outpouring of methane into the ocean.
It is this outpouring of methane into the atmosphere that resulted in extreme global warming and the loss of much terrestrial life. The oceans became acidic as well, and marine species were devastated. It was then that trilobites became extinct, and ammonites barely survived (later to become much more diverse). Hydrogen sulfide was possibly spewed from the seas as a byproduct of methane production, which could have caused extinction on land. Terrestrial plants went through large ecological changes as there is evidence of a great drying out of the climate. This is likely what also resulted in the extinction of many terrestrial animals. The insect population of Earth was also forever changed. Before the extinction, the Permian possessed an amazing insect diversity, including some of the largest ever discovered. Triassic insects more closely resemble the insects of today.
Methanosarcina is the genus of the culprit bacteria, and relatives of the accused are still alive today. Indeed, a species of these methane-producing organisms lives in the guts of cattle and causes the cow flatulence methane production problems we face. The species that caused the Permian extinction was likely around long beforehand. It wasn’t until Methanosarcina received a gene from another bacterium living in the ocean alongside it that the bacteria became capable of breaking down the carbon reservoirs in the ocean sediment and making methane. Add in the catalyst of an increase in oceanic nickel from volcanoes, and we have a recipe for disaster. Nickel happens to be a necessary element for methanogens, and without it they are limited. The volcanic activity in Siberia during the Permian was a catalyst for an even more deadly event.
The Permian extinction really was a sum of a few things happening at just the right time and it resulted in a massive loss in the biodiversity of our planet. Researchers show us that the Earth’s climate is a very delicate one. it doesn’t take an asteroid the size of a city or a solar flare to cause great change. The Permian extinction was a slow and subtle killing, but all the more deadly than the suddenness of the asteroid that may have killed the dinosaurs. Microbes can truly have a large impact on the geochemical climate of the planet. It is bacteria that are in control of the air we all take for granted – a humbling thought for the vain multicellular organism that is man.
Source: Rothman, D. H., Fournier, G. P., French, K. L., Alm, E. J., Boyle, E. A., Cao, C., & Summons, R. E. (2014). Methanogenic burst in the end-Permian carbon cycle. Proceedings of the National Academy of Sciences, 201318106.