The evolution of tree roots may have contributed to the mass extinction of species

A study led by IUPUI scientists and colleagues in the UK suggests that the evolution of tree roots during the Devonian period, more than 300 million years ago, may have triggered a series of mass extinctions that shook Earth's oceans
.

Evidence for the new view of the anomalous turmoil of Earth's prehistoric period was published in the Bulletin of the Geological Society of America, one of
the oldest and most respected publications in the field of geology.
The study was led by Gabriel Filippelli, the Principal Professor of Earth Sciences in the IUPUI School of Science, and Matthew Smart was a PhD student in his lab when he was conducting the research
.

Filippelli said: "Our analysis suggests that the evolution of tree roots may have filled the past ocean with excess nutrients, leading to algae growth
.
These rapid and destructive algae blooms deplete most of the oxygen in the ocean, triggering catastrophic mass extinction events
.
”

The Devonian period, which occurred between 419 million and 358 million years ago, was known for mass extinction events before life evolved on land, during which it is estimated that nearly 70% of life on Earth went extinct
.

The process outlined in the study, scientifically known as eutrophication, is very similar to the modern phenomenon and, albeit on a smaller scale, currently contributes to widespread "dead zones" in the Great Lakes and Gulf of Mexico, as excess nutrients from fertilizer and other agricultural runoff trigger massive algae blooms that consume all the oxygen
in the water.

The difference is that these past events were most likely driven by tree roots, which absorbed nutrients from the land during the growing period and then suddenly dumped them into the earth's water
during the period of decay.

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

Based on chemical analysis of stony sediments from ancient lake beds — the remnants of which are found around the globe, including samples from Greenland and the northeast coast of Scotland used in the study — the researchers were able to confirm previously discovered high and low levels of phosphorus, a chemical element
found in all life on Earth.

They were also able to identify wet-dry cycles based on signs of "weathering" or soil formation caused by root growth, with high weathering indicating a wet cycle with more roots and low weathering indicating a dry cycle
with fewer roots.

On top of that, the team found that drought cycles coincided with higher phosphorus levels, suggesting that during these periods, dead roots release nutrients into Earth's water
.

Smart said: "It's not easy
to peek into the history of 370 million years ago.
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.
”

Based on the simultaneous occurrence of the phosphorus cycle and the evolution of the first tree roots — a characteristic of the genus Archaeopteryth, which was also the first plant to grow long leaves and grow up to 30 feet tall — the researchers were able to determine that decay of the roots was the prime suspect
behind the Devonian extinction event.

Fortunately, Filippelli says, modern trees don't cause similar damage, because nature has evolved systems
that balance the effects of decaying wood.
The depth of modern soil also retains more nutrients than the thin layer of earth that covered the ancient earth
.

But the dynamics revealed by the study reveal other new threats
to Earth's marine life.
The study's authors note that others have made the argument that pollution from fertilizers, feces and other organic waste, such as sewage, has left Earth's oceans "on the brink of hypoxia," or a complete lack of oxygen
.

"These new insights into the catastrophic consequences of ancient natural events may be a warning about
the consequences of similar situations arising from human activity today," Filippelli said.

Enhanced terrestrial nutrient release during the Devonian emergence and expansion of forests: Evidence from lacustrine phosphorus and geochemical records