The evolution of tree roots may have led to mass extinctions

The evolution of tree roots may have led to mass extinctions

The evolution of tree roots may have led to mass extinctions

The evolution of tree roots may have led to mass extinctions

Scientists are collecting rock samples on Ymer Island in East Greenland, one of several sites whose analysis has provided insight into the chemical composition of Devonian lake beds. Credit: John Marshall, University of Southampton.

The evolution of tree roots may have triggered a series of mass extinctions that rocked Earth’s oceans during the Devonian period more than 300 million years ago, according to a study led by scientists at IUPUI, along with colleagues from the United Kingdom.

Evidence for this new view of a highly variable period in Earth’s prehistory is reported in GSA Bulletin. The study was led by Gabriel Filippelli, Chancellor’s Professor of Earth Sciences in the School of Science at IUPUI, and Matthew Smart, Ph.D. student in his laboratory during his studies.

“Our analysis shows that evolution tree roots probably flooded by oceans excess nutrientscausing massive algal growth,” Filippelli said. “These rapid and destructive algal blooms would deplete most of the ocean’s oxygen, triggering catastrophic mass extinction events.”

The Devonian period, which occurred 419 million to 358 million years ago, before the evolution of life on land, is known for its mass extinction events, during which it is estimated that almost 70% of all life on Earth disappeared.

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

The difference is that those past events were likely fueled by tree roots, which pulled nutrients from the soil during growth periods and then dumped them suddenly into the Earth’s water during decay times.

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

Based on chemical analysis of rock deposits from ancient lakebeds—remains of which exist around the world, including 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 that found in all life on Earth.

They were also able to identify wet and dry cycles based on 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.

Crucially, the team found that dry cycles coincided with higher phosphorus levels, suggesting that the dying roots were releasing their nutrients into the planet’s water during that period.

“It’s not easy to look back more than 370 million years,” Smart said. “But rocks have long memories, and there are still places on Earth where you can use chemistry as a microscope to unravel 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 a height of 30 feet—the researchers were able to pinpoint the decay of tree roots. as the prime suspect behind the Devonian extinction event.

Fortunately, Filippelli said, modern trees don’t cause similar destruction because nature has since developed systems to counterbalance the effects 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 uncovered in the study shed light on other more recent threats to life in Earth’s oceans. The authors of the study note that others have made the argument (as in Science 2016) that pollution from fertilizers, manure and other organic waste, such as sewage, has brought Earth’s oceans to the “edge of anoxia”, i.e. 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 resulting from human activities today,” Fillipelli said.

More information:
Matthew S. Smart et al, Enhanced Terrestrial Nutrient Release During Devonian Emergence and Forest Expansion: Evidence from Lake Phosphorus and Geochemical Records, GSA Bulletin (2022). DOI: 10.1130/B36384.1

Andrew J. Watson, Oceans on the Edge of Anoxia, Science (2016). DOI: 10.1126/science.aaj2321

Citation: Evolution of tree roots may have driven mass extinctions (2022, November 9) Retrieved November 10, 2022, from

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