[spoiler]Convergence is the assimilation of an entire planet's biosphere, culminating in a moon-sized apex predator capable of interstellar travel. The reason there's no aliens except necromorphs in Dead Space is because the moons [i]ate every last one[/i]. The last race to fall to the Markers saw their end coming and took steps to stop Convergence; they froze their own planet. They stopped the inevitable and systematic destruction of all life and potential life in the galaxy at the price of their own race's continuity, which is the greatest act of love I've ever heard of.[/spoiler]