Earth is the home world of humanity.
The greatest threat to the Earth and to humanity was always humanity, right up until the late 23rd and early 24th century. This period, referred to as the Age of Discovery, began with the planet on the brink of complete ecological collapse. The ecosystem of planet Earth was almost destroyed by centuries of industrial pollution, chronic overpopulation, and incessant warfare including the use of nuclear biological and chemical weaponry.
To prevent this catastrophe and the probably extinction of humanity and all life on Earth, the Earth Administration Authority was founded. The Earth Administration Authority, or EAA, took control from the surviving nation-states and other factions, and united humanity in the common effort to salvage their home world.
First Contact with the Shaltari led humanity to the Cradle Worlds allowing the EAA to finally ease the overpopulation pressures and to create self sufficient human colonies off the still damaged Earth.
During the Age of Expansion. Discovery humanity spread further still, to The Colonies. This had little impact upon Earth’s overpopulation problems but the influx of resources did aid the ongoing centuries old planetary restoration efforts.
Humanities time on Earth was limited. The fall of the White Sphere in 2506, then The Warning on May 1st of that year, the formation of the abandonist movement and its exodus along with the Battle of Vega, and then the Invasion of the Scourge two days later.
Currently planet Earth is occupied by the Scourge.