We have learned before that oxygen levels decrease, creating mass extinction on Earth. Besides, the evolution of tree roots may have driven mass extinctions, according to a new study.

Published in the Geological Society of America Bulletin on November 9 and conducted by researchers at Indiana University–Purdue University Indianapolis (IUPUI) and colleagues in the United Kingdom, the recent study revelaed that the emergence of tree roots may have set off a sequence of major extinctions that shook the Earth's waters around 300 million years ago.

"Our analysis shows that the evolution of tree roots likely flooded past oceans with excess nutrients, causing massive algae growth," said Gabriel Filippelli, Chancellor’s Professor of Earth Sciences in the School of Science at IUPUI.

"These rapid and destructive algae blooms would have depleted most of the oceans’ oxygen, triggering catastrophic mass extinction events," he also added.

As stated in the release of IUPUI, before the evolution of life on land, during the 419 million to 358 million-year-old Devonian Period, there were a number of catastrophic extinction events that are thought to have killed off over 70 percent of all life on Earth.

This process gave the study its shape. Scientifically known as eutrophication, it is also fueling broad dead zones as excess nutrients from fertilizers and other agricultural runoff triggers, massive algae blooms that consume all of the water’s oxygen like in the Great Lakes and the Gulf of Mexico.

Strong tree roots.

ChristianNasca/iStock

The distinction is that these historical occurrences were probably fueled by tree roots, which during periods of growth drew nutrients from the land and then abruptly dumped them into the water of the Earth. From Filippelli'is point of view, the theory is based on a combination of new and existing evidence.

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

"It’s not easy to peer over 370 million years into the past," Smart said. "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," explained Matthew Smart, a Ph.D. student in Gabriel Filippelli's lab.

Phosphorus cycles took place at the same

The researchers were able to identify the decay of tree roots as the primary suspect behind the Devonian Periods extinction events since the phosphorus cycles took place at the same time as the evolution of the first tree roots, a characteristic of Archaeopteris, which was also the first plant to grow leaves and reach heights of 30 feet.

"Nature has since developed methods to counteract the effects of rotting wood, so new trees don't inflict similar devastation. In comparison to the thin layer of soil that covered the old Earth, modern soil is deeper and contains more nutrients," Filippelli said.

However, the study's findings on dynamics provided insight into other, more recent dangers to ocean life. The authors of the paper point out that other people have argued that fertilizer, manure, and other organic waste pollution, including sewage, have brought the oceans of the Earth dangerously close to becoming completely without 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 the human activity today," Filippelli said.

Study Abstract:

The evolution of land plant root systems occurred stepwise throughout the Devonian, with the first evidence of complex root systems appearing in the mid-Givetian. This biological innovation provided an enhanced pathway for the transfer of terrestrial phosphorus (P) to the marine system via weathering and erosion. This enhancement is consistent with paleosol records and has led to hypotheses about the causes of marine eutrophication and mass extinctions during the Devonian. To gain insight into the transport of P between terrestrial and marine domains, we report geochemical records from a survey of Middle and Late Devonian lacustrine and near-lacustrine sequences that span some of these key marine extinction intervals. Root innovation is hypothesized to have enhanced P delivery, and results from multiple Devonian sequences from Euramerica show evidence of a net loss of P from terrestrial sources coincident with the appearance of early progymnosperms. Evidence from multiple Middle to Late Devonian sites in Greenland and northern Scotland/Orkney reveal a near-identical net loss of P. Additionally, all sites are temporally proximal to one or more Devonian extinction events, including precise correlation with the Kačák extinction event and the two pulses associated with the Frasnian/Famennian mass extinction. For all sites, weathering, climate, and redox proxy data, coupled with nutrient input variability, reveal similar geochemical responses as seen in extant lacustrine systems. Orbitally forced climatic cyclicity appears to be the catalyst for all significant terrestrial nutrient pulses, which suggests that expansion of terrestrial plants may be tied to variations in regional and global climate.