Deep-seated shenanigans.

Although Earth's inner core is solid iron, it may flow extremely slowly, its insides oozing out over millions of years, according to a new study of earthquake waves passing through the planet's heart.

Barbara Romanowicz and her colleagues at the University of California, Berkeley analyzed seismic data to determine why the core favors vibrations moving parallel to the axis of rotation. Such waves pass through the core faster than those moving in other directions.

Past studies explained the pattern by suggesting that iron crystals in the inner core line up in the preferred direction, causing the core to act as a giant iron crystal. Data from more recent quakes do not support such a simple crystal alignment, the Berkeley scientists report in the Nov. 8 Science. Instead, their findings point to a more complex crystal pattern that could arise from convection within the solid inner core.

Because of its extreme heat and pressure, the solid iron may be soft enough to flow. According to available data, iron in the center of the inner core appears to flow parallel to the spin axis, much as if the core of an apple were to ooze toward its stem. Once the iron reaches the surface of the inner core, it spreads outward and flows along the surface of the sphere. Eventually, it reaches the opposite pole and dives back inward.