At the Earth's Core(s)

Did Earth's Twin Cores Spark Plate Tectonics? : Discovery News: "Jan. 6, 2009 -- It's a classic image from every youngster's science textbook: a cutaway image of Earth's interior. The brown crust is paper-thin; the warm mantle orange, the seething liquid of the outer core yellow, and at the center the core, a ball of solid, red-hot iron.

Now a new theory aims to rewrite it all by proposing the seemingly impossible: Earth has not one but two inner cores."