Earth has been long abandoned due to its toxic atmosphere. It is now overgrown with mutated jungle structures that have devoured most of the prior signs of civilisation. Infestation and roaming wildlife still inhabit its surface, but anything of value was stripped by scavengers generations ago.
Most of the wildlife observed today can be traced back to creatures of Earth. In the Orokin Age, organic manipulation was used to modify Earth lifeforms to a purpose: war, agriculture, pets. Long after their Orokin masters perished, some of these species managed to survive through adaptation, and can be found roaming in natural environments.
Like most living organisms, the Grineer require water to survive. Beneath Earth’s towering forest canopy are rich reserves of fresh water that the Grineer have fought hard to maintain for many years. Evidence of their long-standing occupation is found among their many outposts that have been taken hold by giant roots, moss, and other layers of vegetation over time.