Earth

Earth (Terra in Ancient, Midgard to the humans settled by the Asgard, Tau'ri in Goa'uld, and designated P2X-3YZ by the Tau'ri themselves), is the home planet of the Tau'ri and the cradle of human civilization in the Milky Way.

History
Earth was the second planet that the Ancients colonized when they left their home galaxy. Known to them as Terra, it was the center of their empire in the Milky Way and was from where they launched Destiny, a ship designed to explore the universe. Earth was also, home to the city of Atlantis situated in Antarctica which was then much closer to the equator. Around thirty to fifteen million years ago, the Ancients were forced to leave in Atlantis for Pegasus due to a plague. They eventually returned after the war with the Wraith where some chose to join the native humans and integrate into human society, passing on the ATA gene. They also influenced societies such as the Greeks and Romans, inspiring the myth of Atlantis and passing on their language. Shortly after all the Ancients had ascended, integrated into the primitive societies or died, leaving the remaining humans in a primitive and defenseless state, the Goa'uld known as Ra, discovering Earth and its inhabitants, took it for his own and ruled for 5,000 years. An alternate SG-1 traveled back in time and helped the ancient humans to start a rebellion against Ra, who in turn abandoned the Earth.

Thanks to the rediscovery of the Stargate, the Tau'ri have come to find out that Humans live on other planets in addition to Earth, each with their own unique cultures. As the Stargate program progresses, the term Tau'ri eventually came to be used to specifically identify humans from Earth.

Earth has one of the largest human populations of any planet in the known galaxies.

Alternate realities

 * In an alternate reality Earth was attacked by Apophis and most major cities were destroyed. Efforts to combat the invasion were headed in Cheyenne Mountain by the SGA. Samantha Carter stated that Washington D.C. and Philadelphia had been lost. Cities that, based on the SGA's map, were almost certainly destroyed include the following: Cairo, London, Moscow, New York City, and Paris. Colorado Springs was presumably destroyed during the attack on Cheyenne Mountain. The Goa'uld attack started in Europe, Asia and Africa before spreading to the United States. Since the destruction started on the East Coast and moved west and Daniel Jackson left the reality when it reached Colorado, the annihilation of the West Coast was unseen.


 * In an alternate reality Earth was attacked by Apophis and the SGC was invaded. Earth was saved when Samantha Carter successfully contacted the Asgard.


 * In the alternate timeline created by Ba'al, Earth was attacked by a Goa'uld fleet.


 * In an alternate reality, Earth came under attack by a Hive ship, but it was destroyed by the Ancient weapons platform. A single Wraith survived and was later killed, but not before sending a message that was picked up by the ZPM powered hive in our universe, telling it the location of Earth and about the weapons chair.

Behind the scenes
While never given a planetary designation during any of the on-screen material other than "Earth" or "Tau'ri". Earth is identified as P2X-3YZ in the Secrets Files of the SGC bonus features on the Stargate SG-1 DVDs. In these features, the "viewer" is said to be viewing top secret SGC files which give the viewers location as being P2X-3YZ.