Geologists Discover a Critical Kill Mechanism Behind a 350 Million-Year-Old Series of Extinctions

Animak Skull Extinction Desert

The Bakken Shale Formation has offered a new insight into Earth’s geological history, revealing a major trigger for several biotic crises during the late Devonian Period: euxinia, or oxygen depletion and hydrogen sulfide expansion in large water bodies. This research not only helps understand Earth’s past but also warns of potential consequences of global warming, such as decreased diversity and increased extinction rates.

A major oil source in North America reveals insights into one of the planet’s most devastating mass extinctions.

The Bakken Shale Formation, spanning an area of 200,000 square miles beneath parts of Canada and North Dakota, has been a prolific source of oil and natural gas for North America for the past 70 years. Recent findings have now unveiled that these rocks offer a unique insightful glimpse into the intricate geological history of our planet.

A team of researchers, consisting of geologists from the University of Maryland, George Mason University, and the Norwegian oil and gas company Equinor, have devised a novel approach for studying the paleontological and biogeochemical information gleaned from the formation’s rock.

Using this technique, the team pinpointed a major trigger of several closely spaced biotic crises during the late Devonian Period almost 350 million years ago: euxinia, or the depletion of oxygen and expansion of hydrogen sulfide in large bodies of water. Recently published in the journal Nature, the team’s findings demonstrate links between sea level, climate, ocean chemistry, and biotic disruption.

Bakken Shale Team Analyzing Rock Samples

Researchers observe and discuss rock samples taken from Bakken Shale Formation. Credit: Alan Jay Kaufman

“For the first time, we can point to a specific kill mechanism responsible for a series of significant biotic disruptions during the late Devonian Period,” said UMD Geology Professor Alan Jay Kaufman, a senior author of the paper. “There have been other mass extinctions presumably caused by expansions of hydrogen sulfide before, but no one has ever studied the effects of this kill mechanism so thoroughly during such a critical period of Earth’s history.”

According to Kaufman, the late Devonian Period was a “perfect storm” of factors that played a large role in how Earth is today. Vascular plants and trees were especially crucial to the process; as they expanded on land, plants stabilized soil structure, helped spread nutrients to the ocean, and added oxygen and water vapor to the atmosphere while pulling carbon dioxide out of it.

“The introduction of terrestrial plants capable of photosynthesis and transpiration stimulated the hydrological cycle, which kick-started the Earth’s capacity for more complex life as we know it today,” Kaufman said.

The Devonian Period ended around the same time the Bakken sediments accumulated, allowing the layers of organic-rich shale to ‘record’ the environmental conditions that occurred there. Because the Earth’s continents were flooded during that time, various sediments including black shale gradually accumulated in inland seas that formed within geological depressions like the Williston Basin, the preserved the Bakken formation.

Undergraduate laboratory assistant Tytrice Faison (B.S. ’22, geology)—who joined Kaufman’s lab after taking a course with him through the Carillon Communities living-learning program—prepared and analyzed more than 100 shale and carbonate samples taken from the formation. After analyzing the samples, Kaufman, Faison, and the rest of the Bakken team deciphered clear layers of sediment representing three key biotic crises known as the Annulata, Dasberg, and Hangenberg events, with the last crisis associated with one of the greatest mass extinctions in Earth history.

“We could see anoxic events distinctly marked by black shale and other geochemical deposits, which are likely linked to a series of rapid rises in sea level,” Kaufman explained. “We suspect that sea levels may have risen during the pulsed events due to the melting ice sheets around the South Pole at this time.”

Higher sea levels would have resulted in the flooding of interior continental margins, or the transitional region between oceanic and continental crusts. In these settings, high levels of nutrients, such as phosphorous and nitrogen, could have triggered algal blooms which create low oxygen zones in large bodies of water. These zones in turn would have increased toxic hydrogen sulfide right where most marine animals would have lived. Under those conditions, animals in the oceans and on land around the shoreline would have died during these late Devonian events.

The team’s research is not exclusive to global biotic disruptions from hundreds of millions of years ago. Kaufman suggests that their findings are not just applicable to the shallow inland seas of the Devonian Period, but perhaps also to the oceans of today affected by global warming. He compared the ocean’s circulatory system to a “conveyor belt” carrying nutrients, oxygen, and microorganisms from place to place.

“Cold, salty water develops in the North Atlantic region before it sinks and eventually makes its way to the Indian and Pacific Oceans, cycling around the globe. This oceanic jet stream helps to spread life-sustaining oxygen through the oceans,” Kaufman explained. “If that conveyor belt were to be slowed down due to global warming, parts of the ocean might be deprived of oxygen and potentially become euxinic.”

The collateral damage caused by global warming might then promote animal migration out of dead zones or put Earth on a path to decreased diversity and increased rates of extinction, he added.

“Our study helps us to understand several things about Earth’s growing pains across a critical transition from a world we would not recognize today to one we would find more familiar,” Kaufman said. “It provides evidence for a kill mechanism that may be general to many of the many mass extinctions that occurred in the past, but also explains the origin of a major source of oil and gas to the United States.”

Reference: “Basin-scale reconstruction of euxinia and Late Devonian mass extinctions” by Swapan K. Sahoo, Geoffrey J. Gilleaudeau, Kathleen Wilson, Bruce Hart, Ben D. Barnes, Tytrice Faison, Andrew R. Bowman, Toti E. Larson and Alan J. Kaufman, 8 March 2023, Nature.
DOI: 10.1038/s41586-023-05716-2

The study was funded by Equinor.

10 Comments on "Geologists Discover a Critical Kill Mechanism Behind a 350 Million-Year-Old Series of Extinctions"

  1. Oxygen is depleted only when marine productivity exceeds the ability of aerobic respiration to recycle the organic biomass. The Bakkan oil reflects that high productivity as biomass that sank below the oxygen minimum zone to be preserved in sediments being deposited at that time. Black shales don’t accumulate because the environment was reducing, They accumulate because organic matter was abundant to make the environment reducing. Life at that time must have been abundant and the oxygen it created couldn’t keep up with the biomass sinking to become black shales and oil. If sea level rose it was independent of organic matter burial, including limestones that stored CO2 as carbonate shells. Both releasing oxygen.

  2. Clyde Spencer | April 15, 2023 at 9:24 pm | Reply

    It is a stretch to believe that the warm, shallow inland seas, and limited land with primitive vegetation is a good analogue for today.

  3. For those of us who don’t have a geology background you need to speak to us in simpler terms. This is for the purpose of reaching a higher number of people who need to know this information instead of what I would call” preaching to your own geological choir”. I know it would require more effort on your part but it’s worth it ROCKS ARE ALIVE !! How bout that for simplicity ?

    • Clyde Spencer | April 16, 2023 at 8:32 am | Reply

      “ROCKS ARE ALIVE !!”
      Simple, but wrong.

      To whom are you speaking? I’m usually looking for comments from my peers. However, if you are willing to put in more effort and meet me half-way, I’d be glad to put in the effort to explain something, if you have a specific question. In case I get hit by a big EV truck tomorrow, you might want to consider putting in the effort to educate yourself on the topics at hand, rather than expecting to be spoon fed. I have found that Wikipedia usually does a good job of explaining technical subjects. You might want to start by using your online search engine and looking for “Devonian.”

      One of the problems with trying to dumb something down to the lowest level is that often the meaning or implications get changed. If you have an interest in geology, but don’t want to take a class or read a textbook, I can highly recommend the eminently readable books by John McPhee:

  4. ‘I’m the smartest person in the room…’,
    Also, ‘I can highly recommended the eminently readable books…’. Trying so hard to sound so smart and ruined it all in the end. Hilarious.

    • Clyde Spencer | April 17, 2023 at 8:04 am | Reply

      Well, DICK, if you have a problem with John McPhee, I suggest that you take it up with him. You might want to consider professional help for your insecurity.

  5. Alan Drew Barone | April 16, 2023 at 10:51 am | Reply

    What are the titles of John McPhee’s
    I am an amateur geologist and I am very Interested!

  6. I recommend the Bible as a a good read to explain this “mass extinction”. Of course everyone would rather pretend God doesn’t exist so they can live their lives how they see fit rather than answer to a higher authority. It’s mind blowing the theories and hypothesis we come up with to explain away God. Keep aging that rock by the fossil and fossil by the rock.

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