Seismic waves are racing through the Earth at mysterious speeds—and now, scientists know why. A hidden current of flowing rock 3,000 kilometers below our feet is reshaping our understanding of the planet’s core.
Key Points at a Glance
- Post-perovskite crystals in Earth’s D” layer explain seismic wave acceleration
- Solid mantle rock flows horizontally near the core-mantle boundary
- Breakthrough experiment confirms 50 years of geophysical speculation
- Discovery opens a new frontier for mapping Earth’s internal dynamics
For decades, geoscientists have speculated about strange behavior deep beneath the Earth’s surface. Now, a discovery from ETH Zurich has uncovered the astonishing reality: 3,000 kilometers down, solid rock is flowing—and it’s aligning crystals that make seismic waves race.
At the heart of this mystery lies the D” layer, a zone near the boundary between the Earth’s mantle and its molten outer core. Seismic waves, which normally slow down when traveling through solid rock, behave unexpectedly here. They accelerate sharply, as if hitting a different material entirely. Since the 1970s, scientists have puzzled over this oddity.
Enter Professor Motohiko Murakami and his team at ETH Zurich. Their latest study, published in Communications Earth & Environment, delivers the long-awaited answer. The culprit is a mineral called post-perovskite, formed under intense heat and pressure from its precursor, perovskite—the dominant component of the lower mantle.
But here’s the twist: it’s not just the presence of post-perovskite that speeds up seismic waves. It’s how the crystals align. Using advanced computer models and groundbreaking laboratory experiments, the team demonstrated that post-perovskite’s hardness—and thus its influence on wave speed—depends on crystal orientation.
“Only when all the crystals point in the same direction do we see the seismic acceleration observed in nature,” said Murakami.
So what aligns the crystals? The answer is as groundbreaking as the result itself: the solid mantle rock at this depth is flowing—slowly but with immense consequence. Like convection in boiling water, the mantle is churning. But unlike lava, this flow occurs in solid rock, moving horizontally just above Earth’s core.
This hypothesis, long debated in geophysics, is now proven. Murakami’s lab reproduced the conditions of the D” layer, and the crystal alignment—and associated wave speed jumps—matched real-world seismic data.
“This is the final piece of a puzzle we’ve been working on for decades,” said Murakami. “It shows our planet is alive all the way to its deepest interior.”
The implications are profound. This movement deep within the Earth doesn’t just explain seismic anomalies—it may be the hidden motor behind everything from volcanic activity to the drift of tectonic plates. Some even speculate it could influence the Earth’s magnetic field.
What was once theory has now become physical certainty. And with this knowledge, scientists are poised to map internal flows across the globe, creating new models of Earth’s interior dynamics that were once unimaginable.
This discovery doesn’t just close a chapter in geoscience—it opens a new one. With tools now proven to simulate and measure the unimaginable, we may soon understand how the deepest currents of Earth shape our surface world. From earthquakes to volcanoes, the origins of planetary power may start far deeper than we ever thought possible.
Source: ETH Zurich
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