The Earth is the third planet from the Sun and is considered to be the densest and fifth largest planet in the Solar System, though most of its surface is covered in water. It is also the only terrestrial object known to support life. It formed approximately 4.54 billion years ago. Before the First Civilization various species inhabited Earth, such as the Dinosaurs. It is unknown what species the Isu evolved from, but it is most likely that they evolved from primates.
For several thousand years prior to the Great Catastrophe (75000 BCE) Earth was dominated by the Isu, a progenitor race to humanity, whom the Isu artificially created to serve as a docile workforce. Following the Great Catastrophe, an extinction-level event that wiped out most of the Isu and human populations, the Earth was devastated and took tens of thousands of years to restore. When a second catastrophe threatened to once again devastate the Earth on 21 December 2012, the Assassin Desmond Miles made use of the Eye, an ancient Isu construct designed specifically to protect the planet, at a cost to his own life.