Hexbyte Glen Cove Discovery of the oldest plant fossils on the African continent thumbnail

Hexbyte Glen Cove Discovery of the oldest plant fossils on the African continent

Hexbyte Glen Cove

A small plant whose axes divide several times before bearing oval sporangia. Credit: Univeristé de Liège

The analysis of very old plant fossils discovered in South Africa and dating from the Lower Devonian period documents the transition from barren continents to the green planet we know today. Cyrille Prestianni, a palaeobotanist at the EDDy Lab at the University of Liège (Belgium), participated in this study, the results of which have just been published in the journal Scientific Reports.

The greening of continents—or terrestrialisation—is undoubtedly one of the most important processes that our planet has undergone. For most of the Earth’s history, the continents were devoid of macroscopic life, but from the Ordovician period (480 million years ago) green algae gradually adapted to life outside the aquatic environment. The conquest of land by plants was a very long process during which plants gradually acquired the ability to stand upright, breathe in the air or disperse their spores. Plant fossils that document these key transitions are very rare. In 2015, during the expansion of the Mpofu Dam (South Africa), researchers discovered numerous in geological strata dated to the Lower Devonian (420—410 million years ago), making this a truly exceptional discovery.

Cyrille Prestianni, a palaeobotanist at the EDDy Lab (Evolution and Diversity Dynamics Lab) at the University of Liège, explains: “The discovery quickly proved to be extraordinary, since we are in the presence of the oldest fossil flora in Africa and it is very diversified and of exceptional quality. It is thanks to a collaboration between the University of Liège, the IRSNB (Royal Belgian Institute of Natural Sciences) and the New Albany Museum (South Africa) that this incredible discovery could be studied. The study, which has just been published in the journal Scientific Reports, describes this particularly diverse fossil flora with no less than 15 species analysed, three of which are new to science. This flora is also particularly interesting because of the quantity of complete specimens that have been discovered. These plants are small, with the largest specimens not exceeding 10 cm in height. They are simple plants, consisting of axes that divide two or three times and end in reproductive structures called sporangia.”

Mtshaelo kougaensis is a plant that bears complicated sporangia gathered at the end of the axes. Credit: University of Liège

The fossil flora of Mpofu suggests what the world might have been like when the largest plants were no taller than a few centimeters and almost no animals had yet been able to free themselves from the aquatic environment. It provides a better understanding of how the Earth went from a red rock devoid of life to the green planet we know today. These , simple as they are, are a crucial step in the construction of the environments that hosted the first land animals, arthropods. They form the basis of the long history of life on Earth, which continues today from dense tropical forests to the arid tundra of the north.



More information:
Robert W. Gess et al, An early Devonian flora from the Baviaanskloof Formation (Table Mountain Group) of South Africa, Scientific Reports (2021). DOI: 10.1038/s41598-021-90180-z

Citation:
Discovery of the oldest plant fossils on the African continent (2021, June 9)
retrieved 9 June 2021
from https://phys.org/news/2021-06-discovery-oldest-fossils-african-continent.html

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Hexbyte Glen Cove Discovery of new geologic process calls for changes to plate tectonic cycle thumbnail

Hexbyte Glen Cove Discovery of new geologic process calls for changes to plate tectonic cycle

Hexbyte Glen Cove

Elements of a newly discovered process in plate tectonics include a mass (rock slab weight), a pulley (trench), a dashpot (microcontinent), and a string (oceanic plate) that connects these elements to each other. In the initial state, the microcontinent drifts towards the subduction zone (Figure a). The microcontinent then extends during its journey to the subduction trench owing to the tensional force applied by the pull of the rock slab pull across the subduction zone (Figure b). Finally, the microcontinent accretes to the overriding plate and resists subduction due to its low density, causing the down-going slab to break off (Figure c). Credit: Erkan Gün/University of Toronto

Geoscientists at the University of Toronto (U of T) and Istanbul Technical University have discovered a new process in plate tectonics which shows that tremendous damage occurs to areas of Earth’s crust long before it should be geologically altered by known plate-boundary processes, highlighting the need to amend current understandings of the planet’s tectonic cycle.

Plate tectonics, an accepted theory for over 60 years that explains the geologic processes occurring below the surface of Earth, holds that its outer shell is fragmented into continent-sized blocks of solid rock, called “plates,” that slide over Earth’s mantle, the rocky inner layer above the planet’s core. As the plates drift around and collide with each other over million-years-long periods, they produce everything from volcanoes and earthquakes to and deep ocean trenches, at the boundaries where the plates collide.

Now, using supercomputer modelling, the researchers show that the plates on which Earth’s oceans sit are being torn apart by massive tectonic forces even as they drift about the globe. The findings are reported in a study published this week in Nature Geoscience.

The thinking up to now focused only on the geological deformation of these drifting plates at their boundaries after they had reached a , such as the Marianas Trench in the Pacific Ocean where the massive Pacific plate dives beneath the smaller Philippine plate and is recycled into Earth’s mantle.

The new research shows much earlier damage to the drifting plate further away from the boundaries of two colliding plates, focused around zones of microcontinents—continental crustal fragments that have broken off from main continental masses to form distinct islands often several hundred kilometers from their place of origin.

“Our work discovers that a completely different part of the plate is being pulled apart because of the subduction process, and at a remarkably early phase of the tectonic cycle,” said Erkan Gün, a Ph.D. candidate in the Department of Earth Sciences in the Faculty of Arts & Science at U of T and lead author of the study.







Elements of a newly discovered process in plate tectonics include a mass (rock slab weight), a pulley (trench), a dashpot (microcontinent), and a string (oceanic plate) that connects these elements to each other.In the initial state, the microcontinent drifts towards the subduction zone (Figure a).The microcontinent then extends during its journey to the subduction trench owing to the tensional force applied by the pull of the rock slab pull across the subduction zone (Figure b).Finally, the microcontinent accretes to the overriding plate and resists subduction due to its low density, causing the down-going slab to break off. Credit: Erkan Gün/University of Toronto

The researchers term the mechanism a “subduction pulley” where the weight of the subducting portion that dives beneath another tectonic plate, pulls on the drifting ocean plate and tears apart the weak microcontinent sections in an early phase of potentially significant damage.

“The damage occurs long before the microcontinent fragment reaches its fate to be consumed in a subduction zone at the boundaries of the colliding plates,” said Russell Pysklywec, professor and chair of the Department of Earth Sciences at U of T, and a coauthor of the study. He says another way to look at it is to think of the drifting ocean plate as an airport baggage conveyor, and the microcontinents are like pieces of luggage travelling on the conveyor.

“The conveyor system itself is actually tearing apart the luggage as it travels around the carousel, before the luggage even reaches its owner.”

The researchers arrived at the results following a mysterious observation of major extension of rocks in alpine regions in Italy and Turkey. These observations suggested that the tectonic plates that brought the rocks to their current location were already highly damaged prior to the collisional and mountain-building events that normally cause deformation.

“We devised and conducted computational Earth models to investigate a process to account for the observations,” said Gün. “It turned out that the temperature and pressure rock histories that we measured with the virtual Earth models match closely with the enigmatic rock evolution observed in Italy and Turkey.”

According to the researchers, the findings refine some of the fundamental aspects of and call for a revised understanding of this fundamental theory in geoscience.

“Normally we assume—and teach—that the ocean plate conveyor is too strong to be damaged as it drifts around the globe, but we prove otherwise,” said Pysklywec.



More information:
Erkan Gün et al, Pre-collisional extension of microcontinental terranes by a subduction pulley, Nature Geoscience (2021). DOI: 10.1038/s41561-021-00746-9

Citation:
Discovery of new geologic process calls for changes to plate tectonic cycle (2021, May 11)
retrieved 12 May 2021
from https://phys.org/news/2021-05-discovery-geologic-plate-tectonic.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

Read More Hexbyte Glen Cove Educational Blog Repost With Backlinks —