The Earth's double core

The Earth

. The mantle and part of the crust have been cut away here to show the relative sizes of the Earth's fluid and solid cores. The outer fluid core is about 55 percent of the radius of the Earth, and the inner solid core is slightly smaller than the Moon. The Earth's magnetic field is thought to be generated and sustained by moving currents in the planet's electrically-conducting, fluid outer core, which is composed of molten iron. Geophysicists have discovered that the route of the rapid, polar (north-south) waves through the Earth's interior is gradually shifting eastward because the inner core is rotating slightly faster than the rest of the planet. The fast rotation of the inner solid core may help explain how Earth's magnetic field reverses polarity (Courtesy of Paul Richards, Lamont-Doherty Earth Observatory.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University