Earth

Earth is the homeworld of the human species and the capital world of the United Earth Government. Located in the Sol system, Earth is the most populous world within SolCore and the Human Sphere overall. Earth's only major natural satellite, Luna, is also home to a major human colony.

Prehistory
There is evidence suggesting that the planet was visited by one or more ancient civilizations millions of years ago and potentially up until as recently as 300,000-100,000 BCE. Though no unambiguous traces of these visits remain, their existence can be inferred from the presence of decidedly terrestrial out-of-place biota on various extrasolar worlds.

Modern era
By the mid-22nd century, the effects of anthropogenic climate change had begun to take their toll, causing extreme weather, deglaciation and consequently elevated sea levels, as well as desertification. Although the mass adoption of nuclear power for most of Earth's energy needs in the second half of the 21st century had slowed down the process, considerable damage had already been done; for one, entire coastal regions were forced to erect massive seawalls or be submerged. This caused significant human suffering, with intercontinental migrations, poverty, resource wars, and runaway urbanization. As Earth's nations were weakened by global strife, many movements on the off-world colonies sought to assert their autonomy and even gained a foothold on Earth. These crises would come to a head in the Rainforest Wars, which both exacerbated the planet's climate issues and led to a massive death toll and devastation particularly in South America.

In the late 22nd century, the nascent UEG launched the Earth Reclamation Initiative, an ambitious plan encompassing a series of projects to curtail and eventually reverse the ongoing climate crisis. Although previous eco-reclamation projects had been launched by various actors, they had so far been limited in scope and failed to impart long-term change on the global scale. The UEG's projects, developed in tandem with terraforming efforts on Mars and Venus, spanned centuries, with some being concluded only at the cusp of the 26th century. The Initiative involved large-scale reforestation as well as the eventual pioneering of mechanical atmosphere processors and weather-control technologies, made possible by the virtually limitless energy available via fusion power, to expedite the process. This process came with considerable political upheaval and controversy due to the sometimes-draconian measures taken in problem areas. Alongside various contemporaneous civil conflicts, it also led to national governments losing virtually any of the sovereignty they still had remaining. By the 25th century, when Earth's climate had stabilized to such an extent that such crisis conditions were no longer seen as viable or justified, local re-nationalization efforts enjoyed only partial success.

Over the 23rd and 24th centuries, massive arcologies were constructed to contain millions who had once lived in endless slums. In these planned communities, some of which were built in areas that had once been only sparsely inhabited such as Greenland and Siberia, millions of destitute Earthers were given housing and basic amenities. A system of global basic income was instituted as automation continued to render most basic jobs obsolete. Once the system had fully settled into its routine, such an existence was not entirely unpleasant, for basic needs were provided for along with the metaphorical bread and circuses in the form of an infinitude of free, corporate-produced mass media and entertainment. The only way out of this was to migrate off-world, though by the 23rd century, the pioneering spirit of the Golden Age of Space Colonization had long waned and the colonies were no longer the virgin frontiers they had once been. Still, a new life off-world did provide an outlet to many Earthers even before the floodgates opened with the discovery of slipspace travel and the beginning of expansion beyond Sol, first in relatively small numbers the First Wave and then en masse in the subsequent Domus Diaspora. By the late 24th century, colonists no longer needed to be carefully vetted, and colonization companies were practically throwing able-bodied Earthers onto colony ships. This was the first true mass exodus off Earth, and it would continue up until the 26th century.

Society and culture
Earth is often regarded (at least by Earthers themselves) as the cultural heart of the Human Sphere. The stereotypical Earthers are often academics, artists, designers of many varieties, and miscellaneous socialites mingling in slick upper-class penthouse parties. By the 26th century, few Earthers are truly destitute; even those worst-off are provided basic housing and income by the UEG. This is virtually a necessity, given that society has long been so thoroughly automated that there simply are not enough jobs to go around, effectively rendering a significant portion of the planet's population unemployed for life. While this suits some just fine, giving them ample time to pursue their personal passions, it has led to a critical lack of meaning in life to many, sometimes termed "Earther Angst". One way to offset the populace's collective malaise has historically been continual expansion. This is commonly perceived as brain drain, with Earth's best and the brightest generally moving on from their cushy but boring lives on Earth to tame the wild frontier or enlist in the UNSC. This has somewhat changed in the post-war era as Earth and all of SolCore have their own reconstruction projects to contend with, and the standard of living is no longer as high in many places.

Governance and politics
Under the UEG, Earth is divided into administrative territories known as protectorates. Grouped based loosely on the United Nations geoscheme, each of these regions encompasses several of the old nation-states' territories.

Space elevators
Earth has an array of space elevators, six of which are located in major cities also known as "tether cities". These have become commercial hubs of global significance.
 * Mombasa
 * Quito
 * Pontianak - home to the Borneo Space Tether
 * Belem - home to the Amazon Tether
 * Havana - home to the antiquated Centennial Orbital Elevator.
 * Aranuka - ocean platform home to the Pacific Tether before its destruction during the Covenant invasion. Not regarded as a full "tether city" due to its low-capacity nature.
 * Zanzibar - home to a new tether built after the war to replace the Mombasa one.