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Rotation of Earth’s Inner Core Has Slowed
Context:
Research published in Nature from the University of Southern California reveals that Earth’s inner core is backtracking.
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- A USC study shows that the inner core began to slow down around 2010 moving slower than Earth’s surface.
- Confirming a two-decade-long debate over its speed, which some researchers suggest is faster than the planet’s surface.
- The latest study provides the most convincing resolution of the inner core’s slowdown based on two dozen more observations signalling the same pattern.
Key Highlights:
- The Earth’s inner core, a solid iron-nickel sphere roughly the size of the moon, has been a subject of scientific debate for decades.
- Backtracking and Slowing Down: For the first time in approximately 40 years, it is moving slightly slower than the Earth’s mantle.
- Causes: it is attributed to the churning of the liquid iron outer core, which generates Earth’s magnetic field, and gravitational tugs from dense regions of the overlying rocky mantle.
- Seismic Evidence: Scientists cannot directly observe the inner core lies more than 3,000 miles beneath our feet. Instead, they rely on seismic waves from earthquakes to infer its movement.
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- USC researchers analysed seismic data from 121 repeating earthquakes in the South Sandwich Islands between 1991 and 2023.
- Also from twin Soviet nuclear tests (1971-1974) and other nuclear tests by repeated French and American tests from other studies.
- A New Approach:
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- USC scientists used waveforms from repeating earthquakes to create renderings of the inner core’s movement.
- Repeating earthquakes occur at the same location, producing identical seismograms.
- By analysing data from these events, the researchers gained insights into the inner core’s behaviour.
- Impact on Length of Day: Changes in inner core motion can cause the length of the day to vary by a fraction of a second, although this change is extremely subtle and nearly unnoticeable among other natural variations.