Because of your replies in “Farming Invented Twice In Middle East, Genomes Study Reveals”, thought you might like to see this one.
Iron-56 becomes Iron-60 because of neutron capture in aging stars. Iron-60 exists in interstellar space in a band in our Galaxy near the supermassive black hole galactic center where stars are destroyed by its gravitation. I believe there is a process where black holes near the galactic center align with their axis of rotation perpendicular to the axis of rotation of the supermassive black hole galactic center. This has the effect of plowing matter, including iron-60, outward from the galactic center along the center of the galactic plane. The presence of iron-60 as described in this article corresponds to when the earth last crossed the galactic center plane.