A second, far more ancient Stargate, buried in Antarctica for thousands of years. The beta gate perhaps provides the key to how several Earth cultures were taken into captivity and dispersed throughout the galaxy by the Goa'uld. It was accidentally discovered by Jack O'Neill and Samantha Carter after a staff blast bounced the outgoing location to the gate, landing them both in the ice of Antarctica.
The beta gate, much like its counterpart Egyptian Stargate, generated enormous tremors which, Daniel Jackson reasoned, could be detected by global seismic monitoring stations. This led to the United States Air Force successfully retrieving the gate and bringing it to Area 51. It was not long before the beta Stargate was used to smuggle alien technology back to Earth. The beta gate had been moved to an outskirt air strip in Nevada (being used by Rogue N.I.D. agents), where it was intercepted by SG-1. It was then returned to Area 51 where a permanent iris was sealed over its orifice.
The beta gate was retrieved from storage following the destruction of the Asgard mothership Beliskner, and served as the S.G.C.'s gate for two years, until it was attacked by Anubis's Stargate destroyer. With Jack O'Neill piloting the X-302, the beta gate was successfully flown out of Earth's atmosphere and into a hyperspace tunnel where it exploded in space several miles from Earth, sending brilliant flames of light into the daytime sky.
The D.H.D. found with this gate eventually died, proving that the Ancient technology does not have an infinite power source. The beta gate may well be the earliest Stargate ever constructed in the Milky Way Galaxy.
Solitudes - A second Stargate is discovered in Antarctica, buried for thousands of years along with a Jaffa corpse.
Touchstone - The beta Stargate is hijacked by N.I.D. operatives who plan to snatch it away to places unknown.
Fair Game - As a condition for not attacking Earth, the System Lords demand the immediate and unconditional forfeiture of both Stargates from Tau'ri hands.
Nemesis - With the Egyptian gate whisked away from the S.G.C. by Asgard transporter technology, General Hammond orders the beta gate removed from storage immediately to begin active service in the S.G.C.
Redemption, Part 1 - The beta Stargate is attacked by Anubis's Stargate destroyer and is unable to disengage.
Redemption, Part 2 - O'Neill flies the beta gate out of Earth's atmosphere, where it is subsequently destroyed by the Stargate destroyer.