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Two days ago, Ferrebeekeeper wrote about Earth’s magnetic field, an underappreciated invisible force-field which keeps the planet habitable by preventing solar wind from blowing away our atmosphere and oceans (we need those!).  Long ago, Venus and Mars seemingly had liquid oceans and nice atmospheres, but something went wrong (?) with their magnetic fields a billion or so years ago, and just look at them now (tuts censoriously). But maybe we shouldn’t be so quick to judge our neighbors…Five hundred and sixty-five million years ago, the Earth underwent a magnetic crisis too.

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Geologists have been studying fragments of  plagioclase and clinopyroxene from the ancient continental shield of Canada to learn about the state of the planet’s magnetic fields in the ancient past.  As they form, these crystals trap tiny magnetized iron fragments in place like the needles of little compasses.  Scientists can thus study the deep history of the magnetosphere.  As they studied magnetic crystals that were formed 565 million years ago, they found some troubling things: half a billion years ago, the Earth’s magnetic field was over 10 times weaker than what it is today.  Additionally the poles were rapidly fluctuating between north and south at an unexpected rate.

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A closer reading of all of this suggests that 550 million years ago the Earth’s magnetic field nearly collapsed! (for a look at what that means, just walk around Mars).  Life was saved because the solid nickel iron core of Earth nucleated from the molten core at that time.  Instead of a field collapse, our magnetic field became much stronger as the spinning solid inner core and the convection cycles of the molten outer core worked together to form a super geodynamo.  Coincidentally, 541 million years ago is familiar to paleontologists as the inception of the Cambrian explosion, when multitudinous animal life forms appeared on Earth. It is such an important point that it divides the Phanerozoic (filled with mushrooms, megafauna, liverworts, and Roman centurions) from the Proterozoic (billions of years of bacterial soup).   Just a coincidence?

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