Tree Roots Probably Caused Mass Extinctions

Tree Roots Probably Caused Mass Extinctions
Tree Roots Probably Caused Mass Extinctions

When most people think of catastrophic global extinctions, they think of supervolcanoes spewing lava into the countryside or huge fireballs from outer space. But recent studies suggest that a far less aggressive culprit—tree roots—is probably responsible for some of the most devastating extinctions in Earth's history.

In a recent study, scientists examined the reasons behind various population declines that occurred during the Devonian period, between 419 and 358 million years ago. Although the spread of these early terrestrial life forms coincided with a series of marine extinction events that wiped out nearly 70% of the world's aquatic animals, the first plants began to colonize land during this period.

According to previous studies, the emergence of the first plants caused phosphorus levels in the terrestrial environments of Eurasia to drop significantly. This has led to the hypothesis that the first tree roots may have dissolved the rocks and released this important nutrient from the environment.

Phosphorus is essential for all life on Earth, so the emergence of roots must have facilitated tremendous plant growth. However, at the same time, large amounts of phosphorus from decaying and dead plant matter were dumped into the ancient oceans and had a significant impact on marine ecosystems.

According to the study's author, Gabriel Filippelli, "our analysis shows that the emergence of tree roots likely led to massive algal blooms, flooding past oceans with extra nutrients." Much of the oxygen in the oceans would be lost due to these rapid and destructive algal blooms, leading to catastrophic mass extinctions.

This chain of events, known as eutrophication, often occurs in lakes and rivers when too much fertilizer or other anthropogenic food sources contaminate the water.

Researchers examined geochemical records from five Devonian lake beds spanning Greenland and Scotland to find historical evidence of eutrophication. Their findings confirmed a significant decline in terrestrial phosphorus at various time intervals during the Devonian period. More importantly, the timing of these changes matched the ages of the fossilized woody plants, suggesting that the development of rooted trees was the main cause of this nutrient output.

More importantly, the study's authors discovered that these changes often followed devastating extinction events. For example, two significant increases in aquatic phosphorus levels have been shown to coincide with the two main waves of the Late Devonian extinction, which resulted in the extinction of 40% of marine families and 60% of genera.

A detailed examination of the data revealed that phosphorus exports to the ocean occur in cycles and are correlated with changes in local climate. In particular, the change was more pronounced during wetter times, as moisture encourages more plant growth and therefore increases phosphorus flux.

Commenting on the importance of this information, Filippelli says, “This new information about the catastrophic outcome of natural events in the ancient world may serve as a warning about the consequences of similar conditions caused by human activities today.”

Source: iflscience

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