10,000,000 BCE

Circa 10,000,000 BCE, the Precursors choose early humans to be the next species to carry the Mantle. Desiring to seize the Mantle for themselves, the early Forerunners rebel against the Precursors and wipe them out almost entirely. After the Forerunners hunt down all of the Precursors in the Milky Way galaxy, the remains of the race retreat into the Large Magellanic Cloud; the Forerunners' Warrior fleets pursue them via probability mirror-reconciled slipspace portals and proceed to finish their work. A number of Forerunners who conscientiously object to the complete destruction of the Precursors are exiled on a barren planet within the Tarantula Nebula; these Forerunners later remain as the only surviving population of the expedition to the Large Magellanic Cloud.

In the face of extinction, most of the Precursors reduce themselves to inert powder, intending to regenerate their forms later. However, this dust would deteriorate over the coming eons, eventually bringing forth the parasitic Flood. However, one intact specimen remains in deep stasis and is buried within a remote asteroid a million years afterward.