About 251 million years ago, the worst loss of biodiversity ever experienced by our planet took place. It is known as the Great Dying, or more properly as the Permian-Triassic mass extinction: a climate catastrophe that wiped out 81% of the marine species and 70% of the terrestrial vertebrates that existed at the time, and from which our planet took almost 10 million years to recover. The causes are currently uncertain. And while the hypothesis of a period of prolonged volcanic activity in the area of present-day Siberia is usually cited, a new study published in Science indicates a different, possible, culprit: a long period of climate instability, driven by what the authors call a mega El Niño phenomenon.
A shaky hypothesis
The Permian-Triassic mass extinction is usually thought to have been the result of a period of vast volcanic eruptions in the area now known as Siberia, which saturated the atmosphere with CO2, leading to rapid and dramatic increases in temperatures and the subsequent collapse of most terrestrial ecosystems.
Such a scenario, however plausible, does not help to explain the extent of the extinction phenomena that characterized the period: the Permian-Triassic is in fact the only mass extinction that also involved insects, usually extremely resilient to environmental changes, and one of the few to have completely revolutionized plant ecosystems as well.
A vicious climate circle
By studying fossils dating back to the period of the mass extinction, and validating the results using a climate model developed specifically for this purpose, the authors of the new study – led by the University of Bristol and the Wuhan University of Geosciences in China – believe they have obtained a much clearer picture of what happened 251 million years ago on our planet. The available data demonstrate that the increase in temperatures rapidly affected all latitudes, and that these drastic climate changes were driven by a sort of climate vicious circle.
Rising temperatures in the tropics would have led to the emergence of an El Niño phenomenon (a period of high temperatures and changes in global disturbances linked to the warming of the surface waters of the Pacific Ocean) of unprecedented magnitude. “Basically, it got too hot everywhere,” explains Alexander Farnsworth, a researcher at the University of Bristol who worked on the climate models used in the study. “The changes responsible for the climate patterns we identified were profound because they were accompanied by El Niño phenomena that were much more intense and prolonged than those we see today. No species was equipped to adapt or evolve fast enough.”
Life on the brink of disaster
According to the researchers’ reconstruction, the increase in temperatures caused by volcanic eruptions spread rapidly to all latitudes, driven by this unprecedented mega El Niño. This caused the death of vegetation and enormous fires, which devastated all terrestrial ecosystems, releasing further CO2 and eliminating the main natural element capable of eliminating carbon dioxide from the atmosphere (plants). And this contributed to further increasing temperatures, further strengthening the mega El Niño.
Eventually, the planet’s biosphere found itself on the verge of a point of no return. Fortunately, the climate slowly stabilized, and after a few million years, biodiversity began to thrive again, and the dinosaurs emerged as the new masters of the Earth. They would remain so for almost another 200 million years, before a new mass extinction, that of the Cretaceous-Paleogene, wiped them out, handing the planet over to mammals and then, a few tens of millions of years later, to our species.