Two thousand miles underground, giant avalanches are reshaping Earth's inner landscape, says physicist Richard Muller of the University of California at Berkeley. Such turmoil might cause the episodic vanishings and reversals of Earth's protective magnetic field.
Muller has studied the dynamics of Earth's outer core, a molten, iron-rich mass whose circulation powers our planet's magnetic field. As the outer core slowly cools and crystallizes, lighter minerals such as sulfur and silicate get left out. "These minerals drift up and fall like snow, forming inverted mounds," Muller says.
The biggest heaps might accumulate for a million years and rise 300 feet high. If such a pile collapsed, it could alter currents in the core and temporarily shut off Earth's magnetic field. "When the field turns back on, it can have the same polarity or the opposite one. This could explain geomagnetic reversals," Muller says.
A large asteroid impact could trigger a wave of avalanches across the core, Muller suggests, leading to a prolonged magnetic shutdown. Inner disruption could also send a plume of magma rising toward the surface. That link might explain why the giant impact of 65 million years ago, when the dinosaurs went extinct, coincided with huge volcanic eruptions in India.
The GRACE satellite, now mapping Earth's gravitational field, could confirm Muller's hypothesis. "If GRACE sees gravitational changes and there is no surface activity that can account for them, they might be from avalanches," he says.