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      Early plate tectonics was surprisingly speedy

      news.movim.eu / ArsTechnica · Wednesday, 16 August, 2023 - 15:30 · 1 minute

    Image of a small person standing in front of large, reddish rocks.

    Enlarge / 2.7-billion-year-old basalt lava flows in the Pilbara Craton, now tilted about 45 degrees from horizontal. (credit: Jennifer Kasbohm )

    Have tectonic plates changed speed over the last three billion years? The answer has far-reaching implications, as plate tectonics affected everything from the supply of vital nutrients for early life to the rise of oxygen . We know Earth’s interior was hotter early in its history, but did plates move faster because the hotter mantle was squishier, or did the hotter mantle contain less water , which helps mantle minerals flow, slowing plates down?

    A new study , led by Dr. Jennifer Kasbohm of Yale, measured ancient magnetic fields and dated rocks from Western Australia to show that the “Pilbara Craton”—an early continent—moved at quite a clip around 2.7 billion years ago. While today’s fastest plate motion is around 12 cm (4.7 in) per year, the Pilbara Craton moved as much as 64 centimeters (25 inches) per year.

    A rare remnant of early Earth

    In the Archean eon, a time far closer to the formation of our Solar System than to today, basalt oozed over what would later be Western Australia in much the same way it does in Iceland and Hawaii today. Plate tectonics was still relatively new , and continents were in the early stages of emerging from what had largely been a water world . The air was devoid of oxygen, and the most advanced life came in the form of microbial communities that are preserved today in hummocky fossils known as “ stromatolites .”

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      Did giant impacts start plate tectonics?

      news.movim.eu / ArsTechnica · Thursday, 11 August, 2022 - 17:05 · 1 minute

    Artist's depiction of a crater-covered early Earth.

    Enlarge (credit: Simone Marchi/SwRI )

    One of Earth's defining features is its plate tectonics, a phenomenon that shapes the planet's surface and creates some of its most catastrophic events, like earthquakes, tsunamis, and volcanic eruptions. While some features of plate tectonics have been spotted elsewhere in the Solar System, the Earth is the only planet we know of with the full suite of processes involved in this phenomenon. And all indications are that it started very early in our planet's history.

    So what started it? Currently, two leading ideas are difficult to distinguish based on our limited evidence of the early Earth. A new study of a piece of Australia, however, argues strongly for one of them: the heavy impacts that also occurred early in the planet's history.

    Options and impacts

    Shortly after the Earth formed, its crust would have been composed of a relatively even layer of solid rock that acted as a lid over the still-molten mantle below. Above that, there was likely a global ocean since plate tectonics wasn't building mountains yet. Somehow, this situation was transformed into what we see now: The large regions of moving, buoyant crust of the continental plates and the constantly spreading deep ocean crust formed from mantle materials, all driven by the heat-induced motion of material through the mantle.

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