Death in the blink of an eye
251 million years ago, life on Earth faced a disaster like nothing seen before or since. There are many mass extinctions in geologic history, including the end-Cretaceous extinction when the dinosaurs died, and perhaps even one occurring today, but those extinctions pale in comparison to the end-Permian crisis.
At the end- Permian, over 90% of marine species and 70% of land species died. Conditions for life got so bad that it took over 10 million years for the biosphere to really recover; if you go to rocks in the early Triassic, they’re pretty barren.
Unlike the Cretaceous extinction though, where there’s evidence of an asteroid hitting Earth, there’s no single clear explanation for why everything died. There are lots of ideas; giant volcanic eruptions in Siberia, disruptions of ocean chemistry, but no single one seems to do it.
New research led by student Seth Burgess and professor Samuel Bowring from MIT tells an important part of the story. The rocks you’re looking at come from near the city of Meishan China. They’ve been studied extensively because these rocks cross the Permian-Triassic boundary; they record the great dying.
One other thing makes these rocks useful. The rocks are marine limestones intermixed with ash layers. Ash layers erupted by volcanoes are incredibly useful because they contain minerals, like zircon, that can be very precisely dated.
These units have been dated before, but the MIT group made a major step forward by dating the rocks more accurately. They sampled ash layers above and below the Permian-Triassic boundary and found that, remarkably, the 2 layers were separated by only 60,000 years.
90% of the species on Earth vanished in 60,000 years or less.
This result is huge for understanding why the dying happened. The biggest volcanic eruption ever, a huge outpouring of lava known as the Siberian Traps, occurred at about the same time as the end-Permian and scientists have naturally wondered if they were linked. Those volcanoes are also unique in that they interacted with coal layers as they were erupting, a process which could have poured carbon and sulfur into the air. However, 60,000 years is INCREDIBLY fast for the extinction to have been caused by volcanoes.
Those volcanoes were likely active for hundreds of thousands, perhaps millions of years, and the layers that interacted with coal are found throughout the sequence. We don’t have a clue how that much lava could even be formed in 60,000 years, let alone how that much lava could have erupted so fast. If the Siberian Traps did cause the Permian extinction, it has to have been through something that happened incredibly quickly, which just isn’t how those kind of volcanoes normally behave.
The MIT scientists also found one other thing…there’s a big change in the carbon cycle during the 10,000 years preceding the extinction. It’s hard to tell what that means, it could be coal burning caused by the volcanoes or it could indicate other extreme processes in Earth’s oceans. If that process were carbon dioxide being added to the atmosphere, it could have made the Earth warm by more than 10 degrees C in a short time period; possibly enough warming to kill a whole lot of organisms.
Many of the press reports about this paper have said this strengthens the case for the end-Permian being caused by the Siberian volcanoes. There are indications in the Chinese rocks of the Siberian eruptions influencing them so that statement makes sense, but personally, I think the result makes the extinction even tougher to explain. Now though, what really needs done is incredibly detailed work on those rocks to see if we can find a single layer that is unique which could represent the killing event, or perhaps an explanation of how the lava could pour out so fast. Unfortunately, those rocks today are heavily eroded and also found in swamps, making that difficult, but that work is the only way I can see to improve this answer.
Image credit:Shuzhong Shen
P.S. In case anyone reading this wanted to tell Dr. Bowring to have a positive response to my job application…thanks!