Age of the Reapers

12,000 Years ago, the "Forerunner" civilization knew that the end was coming - not a natural disaster, but a "harvest" every 12,000 years. The earth is not a cradle—it is a petri dish. There is an entity in the center of the Milky Way - called the "Reaper" - who uses complex life on the planet as a "maturity mark" and harvests it every 12,000 years. The Forerunners did one thing before their demise: they planted information seeds at 12 geologically stable points around the world. The information is encoded in the geometry of the ruins - waiting to be read by the next generation of civilizations when they are advanced enough.