Earth is the third planet in the Solar System. It is the largest of the Solar System's four terrestrial planets. Earth is the home world of humankind. The planet has one Moon.
On July 2, 1996, Earth was invaded by an alien species called the Harvesters who were seeking to harvest planet Earth's natural resources at the cost of wiping out all life on the planet. Within 48 hours, one-hundred-and-eight human cities were destroyed. On July 4, humanity managed to strike back at the invaders when MIT graduate and environmentalist David Levinson managed to implement a computer virus into the aliens' mothership and disrupting their force-field technology. The mothership was destroyed with a nuclear device thanks to the efforts of Levinson and USMC Captain Steven Hiller, and the remaining aliens are neutralized.
In the aftermath of the invasion, humanity recovered and becomes more politically united against a common threat that almost saw their extinction. In response to possible future extraterrestrial threats, the United Nations created the Earth Space Defense. Within a span of twenty years, humanity has a unprecedented era of peace without a major war or genocide or police action.
On July 3, 2016, on the twentieth anniversary of the War of 1996, Earth was again attacked by the Harvesters. Despite the efforts of the ESD and Earth's planetary defenses, the aliens' massive mothership destroyed the planet's defenses, devastating parts of Europe and Asia, and lands over the North Atlantic Ocean, where it starts to drill down toward the Earth's molten core.
During this time, humanity came into contact with an alien virtual intelligence dubbed the "Sphere" which explained its failed attempt to evacuate Earth's inhabitants and its intentions to unite multiple alien races opposing against the Harvesters. In final act of desperation, the ESD organized a trap—by using the Sphere's presence—to lure and kill the Harvester's Queen out from her ship. The trap partly succeeded, leading to the alien forces falling into disarray and the mothership retreating from Earth.