From the archive: A geological mystery is unfolding far beneath our feet, and it may shed light on the life-sustaining magnetic field that extends far above our heads.
Each year, the solid-iron inner core at the heart of our planet expands by about a millimeter as the Earth’s nether regions cool and solidify. According toThis phenomenon likely dates back to the inner core’s creation, between 1.5 billion and half a billion years ago. At this point, after billions of years of cooling, the Earth’s fiery interior finally lost enough heat to begin an ongoing process of crystallization.
Today, the inner core boasts a radius of about 750 miles . Yet even after an eon of lopsided growth, it hasn’t actually deformed. Gravity acts constantly to mold it, redistributing the excess in the east and maintaining a spherical shape. Besides posing a captivating puzzle, this asymmetrical growth may help power the Earth’s magnetic field .For such a small and distant layer in the colossal onion we call home, the inner core has tremendous influence on us surface dwellers.
That suggests one possible mechanism for the inner core’s uneven cooling. The point of greatest growth beneath Indonesia is a major subduction zone. There, relatively cool chunks of tectonic plates plunge into and chill the burning mantle. “It’s kind of like dropping ice cubes in,” Frost says. This temperature gradient allows the deeper layers to shed their heat, thereby solidifying the inner core.
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