So over two million years ago, the alien species that lived on Tau Volantis discovered a marker which then affected them and they ended up using their superior technology to construct a whole bunch of markers, I'm assuming for research purposes. We don't know the specifics of what happened but apparently enough of them were able to withstand the effects of the marker signal enough to realise what it was trying to do and construct a machine that would flash freeze the planet to contain marker outbreak and even a convergence event itself. I'm kind of assuming that they knew that they couldn't stop the marker from infecting them so the few that were able to built the machine to stop the Necromorphs from achieving convergence while they still had the chance. Convergence finally happened but the alien race succeeded in stopping it from becoming fully realised and the Necromorph moon which resulted was only partially complete. The alien race also knew that all they could do was contain the Necromorph moon but not destroy it since once the button was pushed, their species existence was over. Being the highly intelligent beings they are, they left instructions for any space-faring species that discovered their world to finish what they had started and destroy the moon completely.
Meanwhile, using its marker transmissions, the Necromorph moon sent out a distress signal to all of the markers within its range, including the one on Earth which is still of unknown origin that crashed on our planet 65 million years ago. It was that familiar message "Make us whole" that has been repeated throughout the series which being transmitted. Once anyone got within range of Tau Volantis it also added "Turn it off" to the message. I don't exactly know what it was trying to accomplish or how it was trying to do it, but I think it was trying to get help in the only way it knew how, by actively pinging a marker to instruct its creators into creating copies of the marker which they would seed on other planets. I think the whole "Dead Space" effect that was initially described in early Dead Space works was so that convergence could be prevented. I think the true purpose of the markers, at least the ones created by humanity was to have them seeded on different planets so that eventually humans could use the marker transmission to triangulate them back to Tau Volantis, essentially calling an intelligent species there to turn off the machine that was imprisoning the Necromorph moon. I also think that some of the markers that humans made were faulty, like the one on Titan station which was more concerned about creating a convergence event itself than in helping the Tau Volantis moon with its distress signal.
Flash forward to 200 years before the events of Dead Space where the Necromorph moon is successful in its mission and Tau Volantis is discovered by a research team which is tricked into thinking that they found the marker home world and that there's a machine on the planet that is creating the signal which they should turn off. However, the deception is discovered and the research team which has a military leadership has determined that the entire human race is being under threat and the only way to ensure its survival is to cause an extinction level quarantine of Tau Volantis... which is why everyone killed themselves, they wanted to make sure that no one influenced would be influenced by the signal that was trying to get them to turn off the machine.
Now, when the order is given, a final transmission was sent to Earth by the research team telling the Earth council of what they had discovered. All of the marker sites that were created were quarantined and shut down, extinction level quarantines were ordered for all of those sites such as Aegis VII. The government body that existed at the time was eventually overthrown and EarthGov came into existence which formed out of the factions that opposed the old Earth Council. Now the Markers that were abandoned were hidden away and forgotten, like the one on Aegis VII, and were only rediscovered a couple of hundred years later to just before the events of the first Dead Space game.
Now think about this... what was the marker trying to do when it was discovered and taken off of the planet? It was 1. sending out the distress signal "Make us whole" and 2. it was influencing anyone it could to try to get it to bring the marker back to the planets surface because only from there could anyone have a chance of triangulating a course, using the marker signals, back to Tau Volantis. Of course, once the Aegis VII marker was destroyed, fragments of it were collected and information extracted from those who came into contact with it (Isaac Clarke and Nolan Stross specifically) were used to create a new set of markers which were spread out across different sites across the small corner of the galaxy that humanity had colonised. The new Earth government was making the same mistake the old one had done. The difference is that Ellie seemed to have discovered Tau Volantis before EarthGov since, at the time, they were having to deal with the rise of the Unitologists who, thanks again to the events of Aegis VII, actually came into contact with a marker for the first time since the religions inception from the discovery of the black marker on Earth. In many ways, the Unitologists represent the true intentions of the markers, convergence.
So it seems... Danik was right in a way... the Markers weren't being used for their true purpose since they weren't actively seeking convergence, rather the ones created by humans were distress beacons trying to bring people to Tau Volantis which had a Necromorph moon that hadn't fully completed its own convergence event.
Finally, on the whole issue with the Brethren Moons and how they've been laying dormant for all this time. There are apparently several of these moons in our Milky Way galaxy and possibly countless more in others for all we know... but the ones that are in our galaxy seem to be spread out far enough away from each other since they obviously need entire planets of life to feed on. I think when the Tau Volantis moon sent its distress signal, it did it in a way not to disturb the other moons that were sleeping because it knew that they would just come in and feed on humanity, leaving it incomplete. It's also why I believe the marker on Titan station was faulty since it appeared not to have a so-called "dead space" field around it like the red markers do. A new convergence isn't what it wanted, it just wanted to be freed to complete its own and THEN once it was completed it would consume the rest of Tau Volantis and then come after Earth and its various colonies. Then once it had consumed all life in the area it would have probably created its own markers and fired them off into the galaxy, letting them home in and crash on planets that supported life or was capable of supporting life and just sat there dormant until life was found and one of the markers it sent pinged it.
Of course, this never happened and before the Necromorph moon died, it most likely sent out a signal to its brothers that could hear it that there was life in this part of the galaxy to consume... hence the secret chapter titles being BROTHER MOONS ARE AWAKE... The DLC is definitely going to be something that'll shift the series into a different gear. So far humanity has been dealing with a Necromorph moon in distress... now it may have to come up against a fully formed Necromorph moon or even several.