Well, not really, but I needed a title. This is my own little theory for the marker's actions, and its dissonance between Dead Space 1 and 2. Mind you, I've only played one and two, read some stuff on Wikia, and seen Downfall, so this might contradict some information already presented. But regardless, here's my take on it.
My belief is that the Black Marker, the one on Earth, was created to contain the first (or at least, first known) necromorph outbreak by aliens (either from another planet or previous evolved on Earth and who's civilization was destroyed by the Necromorphs). En encrypted code was put on the Marker's surface which showed the genetic sequence of the Necromorphs because it was the only way to link the Marker to the Necromorphs. If an alien found it they wouldn't understand their language so they couldn't describe what the necromorphs are, and since the necromorphs have so many different shapes for one species they likely thought that if another species was infected that the forms would be so radically different that they couldn't rely on images. The only way to be sure that a species would understand the Marker's connection to the necromorphs was by the one thing that didn't change via all the strands, its genetic sequence. This genetic sequence was encoded so that someone would, hopefully, not randomly put it together and create a new infection, and under the assumption that if one was already suffering from an out break they would already know the genetic sequence and thus link it to the Marker's encrypted one. To further ensure the Outbreak's containment, a sentient computer was put inside the Marker with some sort of telepathic ability; unfortunately the telepathic ability was originally designed for the species that created the Marker, and thus it's use on humans bring about unfortunate results.
How the Marker combats the necromorph invasion, however, involved a two step process.
Step One) Convergence: The marker uses its telepathic ability to call out to all the necromorphs in the area. Once they arrive, it coaxes them to combine into one gigantic necromorph (The Hive Mind). By doing this, the out break is brought into one area where it can be easily controlled, and combining the myriad of independent necromorphs into one form made it easier for the marker to influence and quiet it.
Step Two) Containment: With the necromorph outbreak seemingly contained to one area nearby the Marker, it then coaxes/forces the now giant necromorph to sleep. It then either acts as a warden against the imprisoned necromorph for the rest of eternity (at least until disturbed) or until the collected giant necromorph could be safely destroyed, permanately (dropping a moon or planetoid on the area should do it).
Now, here's some additional thoughts I came up with.
A) Why Didn't The Marker Builders Colony Drop the necromorph outbreak on Earth after the Black Marker contained them?
Answer: Perhaps they did, it was in a giant crater which killed the dinosaurs after all. Perhaps it wasn't a comet that wiped them out but the necromorphs, and the comet was dropped to kill them. For some reason, the Black Marker survived (and thus some of the necromorph material nearby it), or alternatively another Marker was placed on top of the new crater to ensure that any residual necromorph material wouldn't grow. Alteneratively, a necromorph outbreak would have devestated Earth's ecology. Perhaps the aliens believed that the type of energy needed to incinerate all necromorph material would also destroy the rest of the environment, and in the interested of ecological interests they left the Marker to sleep and hope for the best.
B) Why didn't the Marker call the necromorphs in the Ishimura to it and start Convergence, rather than repelling/coaxing them to sleep?
Answer: Maybe it did. After moving the marker in the Ishimura, Isaac was assalted by a host of necromorphs, including the tendrils of a giant creater that might have been growing around the Marker. This was an unusually large assault, even for the sound it made and the attention it could have drawn. Conceivably before hand the marker switched to 'repulsion/sleep' earlier to help protect Vincent after it ran to her, and then projected a hallucination to call for help to contain/destroy the outbreak. Why it didn't do this for Isaac when he was moving the marker to where it wanted to go is unknown, perhaps the awakened Hive Mind was powerful enough to over ride the Marker's influence when it was outside of its field or it believed that Clarke was capable of handling himself.
C) Why Transmit the information to create a new marker, and then try to kill Clarke?
Answer: Well, this one I'm sketchiest about. My best guess is that maybe Red Marker 1 knew that the tectonic plate was crashing down on it, and believed that it wouldn't be enough to kill all of the Necromorph material, especially due to the Ishimura being infected above. Therefore, it believes the knowledge to create a new Marker might be needed if the out break continued (which it did, in Salvage and Ignition). Thus it downloaded the information into Isaac's subconcious, but since the process wasn't designed for a human the information leaked out, causing his dementia. Supposedly the information could be called upon if it was needed, but interference by the government on the Sprawl worsened his condition and then lead to the creation of Red Marker 2 (or 12, supposedly). Since there was no necromorph outbreak however, this wasn't quite the Marker's intention. And then the humans (once again) lead to the creation of the necromorph outbreak again and it finally decides it's better to just leave humans to their fate if a random out break occurs than give them the Marker safeguard.
To this purpose, after the outbreak on the Sprawl the Marker starts its program and initiates convergence. It calls out to all the necromorphs on the station to come to it, where it can contain it. However, the Marker also believes it must eradicate all knowledge of its design from humans. The humans that helped build it (scientists and what not) did not actually understand what they were building, and how, and they would likely die in the out break so they weren't a concern. The main problem was Isaac, who had the entire blue prints stored in its head. Thus the Marker designed to kill Isaac, thus preventing the knowledge from being used again and causing yet another Outbreak. Since Isaac would be dead, he would be infected and taken during Convergence, also ensuring that any informaiton that might linger in a necormorph or dead brain couldn't be used either, possibly. After the necromorphs underwent Convergence and became a new Hive Mind, and Isaac was dead, the Marker would put it to sleep and contain the threat on the station, or hope that the damage it took would plumet the Shard into Saturn and cause its destruction. And thus, it would hope, would finally stop the Necromorph outbreak once and for all since the necromorphs would all be destroyed/contained, and humanity wouldn't have the knowledge to cause another one (supposedly).