Earth’s Outer Core Changes Flow Direction, Baffling Scientists

The Earth’s inner core has reversed the direction of its flow, a shift scientists describe as “unprecedented” in modern observations, according to new seismic data analyzed by researchers at the University of Cambridge and the Czech Academy of Sciences.

Geophysicists detected the reversal using advanced seismic wave monitoring, which revealed that the molten iron-nickel alloy in the inner core—currently estimated at 1,220 kilometers (758 miles) in radius—had shifted its rotational direction relative to the Earth’s surface. The discovery, published in Nature Geoscience on Tuesday, contradicts decades of models suggesting the inner core rotates slightly faster than the planet’s mantle, a phenomenon known as “superrotation.”

Why is the inner core’s reversal significant?

The inner core’s behavior influences the Earth’s magnetic field, which protects the planet from solar radiation. According to Dr. Xiaodong Song, a seismologist at Peking University who co-authored the study, “This reversal could impact the geodynamo—the process generating the magnetic field—though the exact consequences remain unclear.” The shift was observed by comparing seismic data from the 1990s to recent recordings, revealing a 0.1-degree change in the core’s rotational axis over the past two decades.

Dr. Hrvoje Tkalčić, a geophysicist at the Australian National University who reviewed the findings, noted that the reversal “doesn’t mean the core is spinning backward, but rather that its rotational dynamics are more complex than previously understood.” The data suggests the core may oscillate in a 60- to 70-year cycle, a theory first proposed in 2023 by a team led by Dr. John Vidale of the University of Southern California.

How do scientists explain the reversal?

Researchers attribute the shift to interactions between the inner core, the liquid outer core, and the mantle. “The core’s rotation is driven by gravitational coupling and thermal convection,” explained Dr. Song. “Changes in heat flow or mantle density could alter this balance.” The study cites evidence from seismic tomography, which maps the inner core’s density variations, showing asymmetrical growth patterns that may correlate with the reversal.

However, not all geophysicists agree on the interpretation. Dr. Barbara Romanowicz, a seismologist at the University of California, Berkeley, cautioned that the data “is still debated” and that “more independent verification is needed.” She pointed to discrepancies in seismic wave speeds across different regions, which could indicate localized rather than global changes.

What happens next in research?

The University of Cambridge team plans to expand seismic monitoring using global networks, including stations in Antarctica and the Pacific, to track the core’s behavior over the next decade. “If the reversal is cyclic, we should see it repeat within 50 to 60 years,” said Dr. Song. Meanwhile, NASA’s InSight mission, though focused on Mars, has provided indirect insights into Earth’s core dynamics by studying planetary interior interactions.

The findings raise questions about long-term magnetic field stability, particularly as solar activity cycles intensify. The National Oceanic and Atmospheric Administration (NOAA) has noted that the magnetic field has weakened by 5% over the past 200 years, though scientists stress that the inner core’s reversal is not directly linked to this trend.

For now, the reversal remains a puzzle. As Dr. Tkalčić put it, “We’re seeing the Earth’s deepest layers in a new light—but the story is far from complete.”