Swans on Tea

Electric Material in Mantle Could Explain Earth’s Rotation

Well, not really. The electric material could explain some of the small variations in the Earth’s rotation. Not quite the same thing.

Earth’s spin isn’t flawless. Geophysicists have discovered that the time it takes our planet to complete one rotation—the length of a day—fluctuates slightly over the course of months or years. They’ve also noticed extra swing in the predictable wobble of Earth’s axis of rotation, like the swaying of a spinning top. The variations are probably caused by the solid iron inner core, liquid metal outer core, and rocky mantle rotating at slightly different rates. Friction helps bring them into line, and the magnetic field of the outer core can pull on the metal inner core. But to really fit the observations, the core should also exert its magnetic tug on the mantle, says Bruce Buffett, an earth scientist at the University of California, Berkeley, who was not involved in the new study. This means that a layer of the mantle must be able to conduct electricity. But, he says, “the origin of the metallic layer remains an open question.”