Mass Extinctions May Have Been Driven by the Evolution of Tree Roots

Tree Roots

According to new research, the evolution of tree roots may have triggered a series of mass extinctions.

Geologists find parallels between ancient, global-scale extinction events and modern threats to Earth’s oceans.

A series of mass extinctions that rocked the Earth’s oceans during the Devonian Period over 300 million years ago may have been triggered by the evolution of tree roots. This is according to a research study led by scientists at Indiana University–Purdue University Indianapolis (IUPUI), along with colleagues in the United Kingdom.

Evidence for this new view of a remarkably volatile period in Earth’s pre-history was reported on November 9 in the scientific journal Geological Society of America Bulletin. It is one of the oldest and most respected publications in the field of geology. The study was led by Gabriel Filippelli, Chancellor’s Professor of Earth Sciences in the School of Science at IUPUI, and Matthew Smart, a Ph.D. student in his lab at the time of the study.

“Our analysis shows that the evolution of tree roots likely flooded past oceans with excess nutrients, causing massive algae growth,” Filippelli said. “These rapid and destructive algae blooms would have depleted most of the oceans’ oxygen, triggering catastrophic mass extinction events.”

Ymer Island in Eastern Greenland

Scientists collect rock samples on Ymer Island in eastern Greenland, one of several sites whose analysis provided insight into the chemical makeup of lake beds in the Devonian Period. Credit: John Marshall, University of Southampton

The Devonian Period, which occurred 419 million to 358 million years ago, prior to the evolution of life on land, is known for mass extinction events, during which it’s estimated nearly 70 percent of all life on Earth perished.

The process outlined in the study — known scientifically as eutrophication — is remarkably similar to modern, albeit smaller-scale, phenomenon currently fueling broad “dead zones” in the Great Lakes and the Gulf of Mexico, as excess nutrients from fertilizers and other agricultural runoff trigger massive algae blooms that consume all of the water’s oxygen.

The difference is that these past events were likely fueled by tree roots, which pulled nutrients from the land during times of growth, then abruptly dumped them into the Earth’s water during times of decay.

The theory is based upon a combination of new and existing evidence, Filippelli said.

Gabrielle Filippelli

Gabrielle Filippelli. Credit: Liz Kaye, Indiana University

Based upon a chemical analysis of stone deposits from ancient lake beds — whose remnants persist across the globe, including the samples used in the study from sites in Greenland and off the northeast coast of Scotland — the researchers were able to confirm previously identified cycles of higher and lower levels of phosphorus, a chemical element found in all life on Earth.

They were also able to identify wet and dry cycles based upon signs of “weathering” — or soil formation — caused by root growth, with greater weathering indicating wet cycles with more roots and less weathering indicating dry cycles with fewer roots.

Matthew Smart

Matthew Smart. Credit: Photo courtesy Matthew Smart

Most significantly, the team found the dry cycles coincided with higher levels of phosphorous, suggesting dying roots released their nutrients into the planet’s water during these times.

“It’s not easy to peer over 370 million years into the past,” said Smart. “But rocks have long memories, and there are still places on Earth where you can use chemistry as a microscope to unlock the mysteries of the ancient world.”

In light of the phosphorus cycles occurring at the same time as the evolution of the first tree roots — a feature of Archaeopteris, also the first plant to grow leaves and reach heights of 30 feet — the researchers were able to pinpoint the decay of tree roots as the prime suspect behind the Devonian Periods extinction events.

Fortunately, Filippelli said, modern trees don’t wreak similar destruction since nature has since evolved systems to balance out the impact of rotting wood. The depth of modern soil also retains more nutrients compared to the thin layer of dirt that covered the ancient Earth.

But the dynamics revealed in the study shed light on other newer threats to life in Earth’s oceans. The study’s authors note that others have made the argument that pollution from fertilizers, manure and other organic wastes, such as sewage, have placed the Earth’s oceans on the “edge of anoxia,” or a complete lack of oxygen.

“These new insights into the catastrophic results of natural events in the ancient world may serve as a warning about the consequences of similar conditions arising from human activity today,” Fillipelli said.

Reference: “Enhanced terrestrial nutrient release during the Devonian emergence and expansion of forests: Evidence from lacustrine phosphorus and geochemical records” by Matthew S. Smart, Gabriel Filippelli, William P. Gilhooly III, John E.A. Marshall and Jessica H. Whiteside, 9 November 2022, GSA Bulletin.
DOI: 10.1130/B36384.1

Additional authors on the paper are William P. Gilhooly III of IUPUI and John Marshall and Jessica Whiteside of the University of Southampton, United Kingdom. Smart is currently an assistant professor of oceanography at the U.S. Naval Academy. This study was supported in part by the National Science Foundation.

9 Comments on "Mass Extinctions May Have Been Driven by the Evolution of Tree Roots"

  1. “The depth of modern soil also retains more nutrients compared to the thin layer of dirt that covered the ancient Earth.”

    What is the basis for the claim (assumption?) that Devonian soils were necessarily thin?


    • To paraphrase Mark Twain, “Those who don’t read the bible are uninformed. Those who do read it are misinformed.”

    • Tristram Carlyon-Wilson | November 14, 2022 at 12:23 pm | Reply

      What a load of old hooey.Archbishop Ussher of Armagh (the guy that came up with the’Earth-being-6000-years-old’ hypothesis, by adding up the ages of Methuselah & his long-lived relatives) would’ve been proud of you…

  3. Behold the power of the Ents.

  4. This is for so.e of the poorly composed comments I have seen posted to a numerous amount of articles here lately. Not just this article. Some might say that sign of true intelligence is not knowing everything possible about a subject. It is being intelligent enough to realize that you don’t know everything. As well as having the capability to realize, and admit when your wrong. Or possibly don’t know about something. It’s time to wake up and realize the things we are wrong about and that we really don’t know a whole lot about anything. We are infants to not just our universe, but also our planet. I dont believe we are stupid (atleast not the majority) it is pst time to realize our paticular situation. As well as the fact that we have way more knowledge to gain then what we actually have.

    • “As well as having the capability to realize, and admit when your [sic] wrong.”

      I welcome any corrections to things that I write. I’m always willing to learn something new. However, part of my motivation for posting is that I so frequently see things claimed by both authors and commenters that appear to be wrong. I can’t remember the last time someone posted a citation or cogent argument that demonstrated I was wrong. On the other hand, those posting claims based on religious dogma are convinced that they are correct and recognize no authority other than the collection of ancient Judaeo-Christian texts that were sanitized by the Councils of Nicaea.

  5. This is the most r*****ed theory i have ever heard and definitely the winner for today’s waste of time article. P.U. smells like Purdue all over it

  6. Yet another WOW! theory for mass extinction. Something caused them but l will have to check the raw data before forming another strata in my mind – as treetops ain’t much different to tree roots once rotted down.
    And btw – Bishop Ussher was ignorant of radio active decay – among other things!

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