Earth’s Hidden Core Within a Core Revealed by Seismic Echoes
ANU seismologists in 2023 provided evidence that Earth contains an innermost inner core—a roughly 1,300-km-diameter iron sphere with crystal orientation different from the surrounding inner core—reconstructed from global seismic echoes after large earthquakes. This fifth, hidden layer tightens the picture of Earth's deep structure and may reflect an early-formed core or a different iron phase; the same seismic approach is now used to study rocky planets like Mars.