Nearly 700,000 years ago the Earth's core shifted, changed the magnetic field, and precipitated mass extinctions around the globe. Now worried scientists think it may be happening again.
http://beforeitsnews.com/story/598/822/Doomsday:_Earths_core_spinning_out_of_control.html
http://beforeitsnews.com/story/598/822/Doomsday:_Earths_core_spinning_out_of_control.html