Nicole: The Marker's signal changes us. Recombines us. But there's a dead space in that signal, around the Marker itself. The eye of the storm. They can't stay in it for long.
What Tweed said. Originally the 'dead space' was a zone around the marker where the signal and iirc necromorphs themselves couldn't get or got scrambled or smth. It's been years and it was never fully explained. DS1 was still ambiguous about the nature of the markers and toyed with the idea that the modern copy of the marker was 'corrupt' while the og one could shed some light on how to defeat the whole thing.
Pulling things from ass and memory here, mind you. Go search jewtoo for some 7 hours long analysis video or smth. Or just play the game.
