Earth's Inner Core Reversed Relative Spin Around 2010 in a Roughly 70-Year Cycle
Updated
Updated · spacedaily.com · Jun 30
Earth's Inner Core Reversed Relative Spin Around 2010 in a Roughly 70-Year Cycle
1 articles · Updated · spacedaily.com · Jun 30
Summary
Seismic evidence indicates Earth’s inner core slowed to match the surface around 2009-2010, then began rotating slightly more slowly than the mantle and crust above it.
More than 5,000 kilometres down, that “reversal” is only relative: the core still turns in the same direction as Earth, with differences of just fractions of a degree a year.
Studies from Peking University in 2023 and USC in 2024 both support the shift, using repeating earthquakes and old nuclear-test records to track tiny changes in seismic waves through the core.
The broader idea of a roughly 70-year oscillation remains disputed because the data are sparse and some signals could reflect changes in the inner core’s shape rather than its rotation alone.
Geophysicists care because the same decades-long rhythm appears in day-length variations and magnetic-field drift, hinting at angular-momentum exchange deep inside Earth.