Home Radiation Linking mass extinctions to the expansion and radiation of terrestrial plants

Linking mass extinctions to the expansion and radiation of terrestrial plants


Newswise — Boulder, Colorado, USA: The Devonian period, 419 to 358 million years ago, was one of the most turbulent times in Earth’s past and was marked by at least six extinctions major marine events, including one of the five largest mass extinctions on record. to have taken place. Additionally, it was during the Devonian that complex trees and land plants similar to those we know today first evolved and spread across the landscape. This evolutionary advance included the development of large and complex root systems capable of affecting soil biogeochemistry on a scale previously unknown to ancient Earth.

It has been hypothesized that these two seemingly separate events, the marine extinctions and the evolution and expansion of plants, were intimately linked to the Devonian. Specifically, it has been proposed that plant evolution and root development occurred so rapidly and on such a massive scale that the export of nutrients from land to ancient oceans increased dramatically. This scenario is seen in modern systems where anthropogenic nutrient export has dramatically increased nutrient loading in areas such as the Gulf of Mexico and the Great Lakes, resulting in large-scale algal blooms that eventually by depleting the oxygen in the water column. This effect, known as eutrophication, amplified globally, would have been catastrophic for ancient oceans, fueling algal blooms that would have depleted most of the ocean’s oxygen.

The key to linking mass extinctions and the expansion and radiation of land plants lies in identifying a high nutrient flux above background levels, linking this nutrient flux to indirect or direct evidence of the presence of deeply rooted land plants and finally showing that this phenomenon has occurred. in many places and times.

This study, the first of its kind, was able to do just that by using geochemical records from ancient lake deposits in Greenland, northern Scotland and Orkney. Using lake records, high values ​​of nutrient phosphorus were detected at five distinct locations during the height of Devonian plant evolution and expansion. In each case, high values ​​of nutrient supply coincided with evidence for the presence of early trees in the form of fossilized spores and, in some cases, fossilized stems of the earliest deep-rooted tree, Archaeopteris. In two cases, this evidence coincided with a Devonian marine extinction event, including the most significant Devonian mass extinction, the Frasnian-Famennian extinction (also known as the Upper Devonian).

In addition, this study, published yesterday in the Bulletin of the Geological Society of America, linked the periodic wet/dry climatic cycles known to exist in the region during the Devonian with specific episodes of plant colonization. Although high nutrient export was noted during wet and dry climatic cycles, the largest export events occurred during wet cycles, suggesting that plant expansion was episodic and related to climatic cyclicity.

The episodic nature of plant expansion could help explain why there are at least six significant Devonian marine extinctions. Although the scope of this study was limited to a single geographic region, it is likely that these events occurred throughout Devonian Earth. The colonization of different types of land plants in different regions and at different times would have resulted in episodic pulses of nutrients large enough to sustain eutrophication and cause (or at least contribute) to the numerous marine extinction events throughout the Middle Devonian. late.

Enhanced terrestrial nutrient release during the emergence and expansion of Devonian forests: evidence from lacustrine phosphorus and geochemical records
Matthew Smart; Gabriel Philippelli; Guillaume Gilhooly; John Marshall; Jessica Whiteside
Contact person: Matthieu Smart, [email protected]Indiana University–Purdue University Indianapolis, Earth Sciences, Indianapolis, Indiana
URL: https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/doi/10.1130/B36384.1/618814/Enhanced-terrestrial-nutrient-release-during-the

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