An international team of geologists from Poland and the UK has found evidence that the Late Devonian mass extinction, which occurred approximately 370 million years ago, was caused by massive volcanic eruptions.
(A) scheme of Frasnian-Famennian (F-F) global event and two-step Kellwasser crisis, and related volcanic events; (B) locations of F-F sites studied for mercury abundances, compared to inferred proximity to coeval large igneous provinces. Image credit: Racki et al.
The Late Devonian extinction was one of five major extinction events in the Earth’s history. It killed up to 80% species, obliterating the lavish Devonian coral reef ecosystem.
The final pulse in this multi-step crisis, called the Frasnian-Famennian event, was its most devastating. But what, exactly, did the killing?
Now, University of Silesia’s Professor Grzegorz Racki and co-authors have discovered a likely culprit — major volcanism, as revealed by a widespread pulse of mercury.
“Up until now the main debate on this mass extinction has been what the main direct cause was,” Professor Racki said.
“We provide the first clear evidence for volcanism.”
The researchers analyzed rocks from Morocco, Germany, and Siberia, all dating from the same short geologic interval 372 million years ago, just before the Frasnian-Famennian boundary.
In addition to being spread across two continents, the rocks varied from black shale, grey shale, to limestone, and ranged from a few centimeters to a few meters thick.
Yet they all shared one particularly striking characteristic: a sharp mercury peak hundreds of times higher than background.
In other mass extinctions, elevated mercury has been closely linked to big-time volcanic episodes.
“In fact, mercury has become to Earth-based catastrophes what iridium is to extraterrestrial-based ones,” Professor Racki said.
“Mercury as a geochemical fingerprint of volcanism appears decisive in the new stage of mass extinction studies.”
“Now we can say that all of the ‘Big Five’ mass extinctions coincide with major volcanic events,” added team member Dr. Paul Wignall, from the University of Leeds.
“Until our discovery, this Late Devonian extinction was the major exception.”
The findings appear online in the journal Geology.
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Grzegorz Racki et al. Mercury enrichments and the Frasnian-Famennian biotic crisis: A volcanic trigger proved? Geology, published online April 26, 2018; doi: 10.1130/G40233.1
