The marker is sealed evil in a leaky canso, however many millennium ago, the black marker and it's the dead space effect helps keep the necromorphs contained while it is buried, so that none of the bacteria or worms and whatnot that come in direct.
Kyne had told you that the red marker had kept a large creature called the hive mind dormant, and that the necromorph infection was because the mass effect and deadspace core stories are at least broadly the same, they're just told very differently, from very different points if view. As isaac's dementia set in, he began to hear the symbols whispering to him.
