One of the key tenets of geophysics is that Earth’s liquid outer core has always been the source of the dynamo that generates its magnetic field. Magnetic fields form on Earth and other planets that have liquid, metallic cores, rotate rapidly and maintain conditions that make the convection of heat possible.
In 2007, French researchers proposed an unconventional theory that the Earth’s mantle was not entirely solid since the very beginnings of the planet. They proposed that during the first half of the planet’s 4.5 billion year history, the bottom third of the Earth’s mantle was molten. Six years later, researchers Stegmen and Ziegler, showed how this once-liquid portion of the lower mantle, rather than the core, was responsible for the Earth’s magnetic field.
The Earth’s mantle is made of silicate material that is normally a very poor conductor of electricity. One of the studies teams asserted the liquid silicate might actually be more electrically conductive than what was generally believed under intense heat and pressure.
Their computer model found very large values of electrical conductivity which were large enough to sustain a silicate dynamo. If this theory is correct, it would mean the mantle could have generated the young Earth’s first magnetic shield. It could also have implications for how tectonics evolved and may have made life on Earth possible sooner.
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