The Great Dying
Published in the EarthSphere Blog. Feature Image: Caught in the Act of Dying (ArcheanArt)
Prologue
The Forgotten Origins series has wound its way through Earth’s history to the end of the Permian, now reaching a catastrophe called the Great Dying.
Last Time: Permian Water World
The End of Early Life … Almost
The Permian Period came to a catastrophic end 252 million years ago with the extinction of 95 percent of all marine species and 70 percent of terrestrial species. Most of life checked out at the backdoor and disappeared into the ether in an event known as the Great Dying.
Humans are not great planners. Individually we do reasonably well, but as a group, we are prone to procrastination. This flaw is why politics is mostly about reactive policy rather than proactive planning. Why do today what we can put off until it becomes a full-blown emergency?
Perhaps this tendency toward reactive versus proactive decision-making is why we might take a jaded view of the Great Dying and see it more as a historical curiosity than an existential lesson. We might say to ourselves, “how interesting,” instead of “holy crap!”
The end of the Permian serves as a grim reminder to the biosphere about how bad it can get. The planet became virtually uninhabitable for life. Food chains collapsed, and environmental conditions changed too quickly for most species to survive.
It might behoove us to consider what happened at the end of the Permian to cause such a catastrophe and compare that information to conditions today in the Anthropocene. Rapid climate change carries with it the threat of extinction. Eight billion Homo sapiens occupy our planet today, and we expect another two billion more by 2055. Proactive planning does not guarantee success, but not planning guarantees disaster. We can no longer afford to approach our future through a purely reactive lens. We need to do better than that.
More Oxygen Please
The Great Dying nominally occurred 252 million years ago, but debates around the length of the extinction event have produced a range of estimates from 15 million years to 200,000 years. I favor the shorter range since evolution seems to find a way to adapt over long periods, and evolution clearly didn’t adapt during the Permian mass extinction.
It is also possible that harsh conditions weakened the biosphere over a longer period, and rapidly changing conditions at the end of the Permian delivered a coup de grâce.
One of the revealing facts about this mass extinction is the remarkable difference between 95 percent species loss in the oceans and 70 percent species loss on land. The large marine die-off leads some researchers to believe the underlying root cause of this disaster was a lack of oxygen.
We know from our previous discussion in the Forgotten Origins series how oxygen is intimately tied to life on this planet. Low oceanic oxygen levels would have led to suffocation for many species.
Warm water holds less oxygen, and the climate was warm in the Late Permian. Estimates of seawater temperatures at the end of the Permian go as high as 32 degrees C (90 degrees F).
Interestingly, the paleontological data indicate species extinction was greater in higher latitude locations than at the equator, the warmest place on the planet. The theory is that species living in normally warm waters are more adept at surviving under low and variable oxygen conditions. They evolved to deal with the problem.
However, species accustomed to cooler conditions with fewer temperature variations were more sensitive to changes in oxygen levels and unable to adjust to rapidly increasing water temperatures.
Cause and Effect
Oceans are an integral part of the planet’s climate control system. They offer a huge heat reservoir to buffer atmospheric temperature changes. They are the heat pumps of the planet, cooling the atmosphere when it overheats and heating the air when more frigid conditions set in.
If the oceans overheat, the most likely culprit is a superheated atmosphere. Various studies have estimated average global temperatures at the end of the Permian were 20 to 30 degrees C higher than today. The rapid onset of high temperatures would have triggered ocean heating.
Located in the northern regions of Siberia are the remnants of a massive outpouring of flood basalts called the Siberian Traps. Flood basalts occur when Earth’s crust splits open along massive fissures, and the molten core of an underlying mantle plume (hot spot) disgorges onto the planet’s surface. Rivers of lava flow like water, filling in valleys with lakes of molting rock and traversing the topography like a flood from hell. Individual flows travel hundreds of miles before freezing into solid rock.
The Siberian flood basalts covered an area estimated at seven million square kilometers (2.7 million square miles). Over one million cubic miles of rock erupted onto Earth’s surface. For the global biosphere, the basalts were not the threat. But the degassing of the mantle plume pumped carbon dioxide and other greenhouse gases into the atmosphere, triggering rapid global warming and mass extinction.
We may want to ponder the comparison between now and then since the math is simple. The Siberian traps erupted for two million years and raised global temperatures by about 30 degrees C — a rate of 1 degree every 67,000 years. Human activities during the Anthropocene have increased the global temperature by 1 degree C in 150 years.
(Next: The Triassic Begins)
Sources:
What caused Earth’s biggest mass extinction? (Source: Stanford University)
Permian extinction (Source Britannica)
Hyperthermal-driven mass extinctions: killing models during the Permian–Triassic mass extinction (by Michael Benton; Philosophical Transactions of the Royal Society)
Coal-burning in Siberia after volcanic eruption led to climate change 250 million years ago (Source: Science Daily)
