Trees may be responsible for mass extinctions on Earth, scientists say

(ORDO NEWS) — Many researchers, when thinking about catastrophic global extinctions, imagine giant fireballs coming from space, or super volcanoes spewing lava.

However, a new study has found that some of the most devastating extinctions in our planet’s history were most likely the work of tree roots. That’s something you don’t think about when looking at these plants that are useful for all living things.

In a new study, scientists tried to find out the causes of numerous catastrophes that occurred during the Devonian period (419-358 million years ago).

It was during this period that the first plants began to develop on land. Remarkably, the spread of these early terrestrial life forms coincided with a series of marine extinction events that wiped out nearly 70 percent of the world’s aquatic life.

Previous studies have shown that the appearance of the first plants led to a significant decrease in the level of phosphorus in the terrestrial landscapes of Eurasia.

This has led to the theory that early tree roots may have released this essential nutrient from the landscape, breaking down rocks.

All life on Earth needs phosphorus, and therefore the evolution of roots would allow unprecedented plant growth.

However, phosphorus released from dead and decaying plant material would have been released into the ancient oceans in huge quantities, with profound effects on marine ecosystems.

“Our analysis suggests that the evolution of tree roots likely flooded past oceans with an excess of nutrients, causing massive growth of algae,” study author Gabriel Filippelli explained.

“This rapid and destructive algal bloom would have depleted much of the oxygen in the oceans, causing catastrophic mass extinction events.”

This sequence of events (eutrophication) is often seen in lakes and rivers when excess fertilizer or other anthropogenic nutrient sources pollute the water.

To uncover ancient examples of eutrophication, the researchers examined geochemical data from five Devonian lacustrine deposits in Greenland and Scotland.

As expected, their results showed a massive depletion of terrestrial phosphorus at various points in time throughout the Devonian.

Importantly, the dates of these fluctuations correlated with the age of fossil woody plants, suggesting that the appearance of rooted trees was indeed the cause of this nutrient export.

More importantly, the study authors found that these changes often coincided with mass extinction events.

For example, two notable increases in water phosphorus were found to correlate with two major waves of the Late Devonian extinction, resulting in the loss of 40 percent of marine families and 60 percent of genera.

A closer analysis of the data showed that the export of phosphorus to the ocean occurred on a cyclical basis and was consistent with regional climate fluctuations.

More specifically, the shift was enhanced during wetter periods, as wet conditions favored more plant growth and therefore resulted in more phosphorus runoff.

Filippelli explained that “this new understanding of the catastrophic results of natural phenomena in the ancient world may serve as a warning of the consequences of similar conditions resulting from human activities today.”

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