In July of 2010, SG-1 was preparing to celebrate the tenth anniversary of their first mission to P4C-970, which had led to their alliance with the Aschen and Earth's membership in the Aschen Confederation. Earth was at peace, the Goa'uld had been defeated, and Robert Kinsey was president of the United States. Hammond had died six years earlier of a heart attack under suspicious circumstances, Jack had retired and moved to his Minnesota cabin in bitterness when his warnings about the Aschen were ignored, and Carter had married Ambassador Joseph Faxon at least three years before. There was no longer a military, and O'Neill and Carter had both been colonels before their retirement. The stargate was housed at the J.R. Reed Space Terminal in Washington, DC where it was open to the public and used routinely for space travel, and former technician Walter Davis Harriman worked as Operations Tech Advisor at the SGC facility at Cheyenne Mountain, now a tourist attraction.
Aschen advancements in medicine had developed an anti-aging vaccine which caused a 91% drop in the birthrate, but the statistics had been kept secret, and the population was unaware that humanity was on the brink of extinction. When the retired members of SG-1 learned of the Aschen's insidious attempt to conquer Earth, they devised a plan to use time travel to change their own fate. Aschen computers had the capability of predicting solar flares, and SG-1 used this technology to send a message through the stargate, back in time to themselves ten years before, to prevent the Aschen alliance. Although all the members of SG-1 were killed in the attempt to breach security and send the message, the note, which read, "Under no circumstances go to P4C-970. (signed) Colonel Jack O'Neill," was successfully sent, history was changed, and humanity was saved.
Cross Reference: Aschen, Joseph Faxon, J.R. Reed Space Terminal, Mollem, P4C-970, Stargate, Time Travel, Tour Guide
Episode Reference: 2010