POPULATION: 7.9 billion (10 billion pre-war)
Known as Erde-Tyrene to ancient humans, Earth was the homeworld for both ancient humans and modern humans alike. Prior to what is considered modern human history, Earth was thought to be the original homeworld of ancient humanity, though the planet of Charum Hakkor became the center of governance for the ancient human empire long before the start of the Human-Forerunner Wars. Following the defeat of humanity at the hands of the Forerunners, Erde-Tyrene became the new home to what was left of humanity, descendants of those defeated humans, devolved at the hands of the Forerunners as punishment and for study.
Thousands of years after the end of the war, the planet became home to the Didact’s cryptum, placed there following his exile so that his enemies couldn’t find him. His sanctuary was eventually discovered by Bornstellar Makes Eternal Lasting, a curious Forerunner, and Chakas and Riser, two unwitting human accomplices, who inadvertently revived the Didact and were whisked away on his journey for answers.
In modern times, Earth was left untouched by the Human-Covenant War until the very end. When the Prophet of Regret and his Fleet of Sacred Consecration arrived in 2552 in search of the portal to the Ark, they were completely unaware that Earth was populated, let alone the homeworld of humanity they had been searching for. Although he only brought fifteen ships with him, Regret's fleet was still able to punch a hole in Earth's defenses and get to the surface, albeit for a short period of time. The Prophet of Truth would show up soon after with a much larger fleet, having already learned the location of humanity's homeworld, but keeping that information from the other hierarchs. Earth managed to survive both waves of attack, though at a high cost.
After the war, Earth got a small reprieve to conduct repairs and rebuild the Home Fleet, but faced attack again in 2555 by retriever sentinels sent from the Ark to Earth. Attempting to repair the Ark and get revenge on the humans he thought responsible, the monitor of Installation 00 tricked the UNSC into reopening the Portal at Voi and sent sentinels through to harvest the planet. The attack was short-lived, but caused localized damage and the loss of nearly a dozen ships in the Home Fleet.
Two years later in 2557, Earth faced attack yet again from the Didact, who used a Composer to compose the entire population of New Phoenix before being stopped by John-117 and Cortana. This attack was coupled with a ground invasion by Jul 'Mdama's Covenant, who managed to open a portal from Gamma Halo to Earth a the same time as the Ur-Didact's attack. This attack was also short-lived, and managed to spare civilian casualties as the portal was opened into the recently composed New Phoenix, which was now abandoned.