In Operation: CRIMSON SHIELD team Legacy, supported by Rook-R291 and NightStalkers storm a Covenant controlled Precursor compound in hopes to stop the Covenant from activating a fail safe that would obliterate the planet.
Having discovered the location of a Precursor structure, the Covenant attempted to activate what the UNSC thought was a fail safe incase the Forerunner's won the war. Although it was a failsafe, it didn't destroy Earth like they thought it would, instead it unleashed the Flood.
October 21, 2552
- 0610 Hours: UNSC scientists discover the Precursor A.I. becomes active as Covenant glass Earth