Beginning of Plate Tectonics Was More Recent and More Gradual Than Expected Based on Northwest Australian Rocks

      

      Researchers from Cologne University present important new constraints showing that plate tectonics started relatively slowly, although the early earth's interior was much hotter.

       For this research, reported in the January 12, 2021 Proceedings of National Academy of Sciences, geologists and geophysicists led by Dr. Jonas Tusch  investigated up to 3.5 billion year old igneous rocks from northwest Australia that cover 800 million years of earth's early history.

 

      The analysis of these rock successions reveals that the oldest samples exhibit small anomalies in the isotope abundances of the element tungsten (W) that progressively diminish with time. 

     The origin of these anomalies, namely the relative abundance of 182W, relates to ancient heterogeneities in the terrestrial mantle that must have formed immediately after formation of the earth more than 4.5 billion years ago. The novel tool of high-precision 182W isotope measurements to rocks from the Pilbara Craton in Australia, that span an age range from 3.5 billion years to 2.7 billion years, was used in this study.

      The preservation of these 182W anomalies in the igneous rocks from northwest Australia demonstrate that pristine mantle reservoirs from the beginning of our planet were conserved over timescales exceeding more than one billion years during the Hadean time period.

      This finding is very surprising, because higher mantle temperatures in the early earth suggest that mantle convection was more extensive and much faster than today. Interestingly, the observed 182W anomalies start to diminish at around 3 billion years ago, within a geological era that is assumed to mark the beginning of modern plate tectonics. 

     The onset of modern plate tectonics, involving subduction processes and mountain uplift, has been shown to be a key event triggering the emergence of large continental masses and an oxygen-rich atmosphere, all of which set the stage for the origin of more complex life. This artist conception of earth during the Hadean time period (which predates "modern" plate tectonics).

Here's to our oxygen-rich atmosphere of 2021. Breathe deep and sense those plates moving!

Steph [aka WW (Tungsten Tungsten;-))]

Bioturbation: The Worms Crawl In, The Worms Crawl Out

       Bioturbation is the reworking of soils and sediments by animals (including worms, snakes, trilobites, and crustaceans) or plant roots. The worms crawl in, the worms crawl out in these churned, turned over and under soils: check out this bioturbation video and watch the burrowing worms in action.

         These ancient dirt churners were recently determined to have taken much longer to bioturbate than originally thought, by millions of years.

       "For years, scientists thought bioturbation commenced in earnest with the Cambrian Explosion, 541 million years ago, when the complexity and diversity of animal species began to expand dramatically."

        "But that wasn’t the case. In a new study published in the journal Nature Geoscience, researchers found that major bioturbation did not occur until at least 120 million years later, during the late Silurian Period."

      Dr. Lidya Tarhan and researchers at Yale University propose that "Delayed bioturbation may have been responsible for regulating marine sulfate and atmospheric oxygen levels. A previously proposed drop in surface oxygen levels may be tied to the onset of extensive bioturbation, given that “oxygen is directly tied to the burial of organic carbon,” Tarhan said. “Less burial of organic carbon, due to bioturbation, means that more oxygen is used to respire or burn through that carbon, and thus oxygen decreases.”"

      Thank heavens for worms and other bioturbators!

     And of course, there's evidence of mass bioturbation (wait for it. . .):

As the Worm Turns,
Steph

       I am not especially fond of the color pink, but I do like these kindergartners' style for our "NOVEMBER is CHEMISTRY MONTH" experiment with Chromatography and ROY G BIV.