The mystery surrounding who or what created the Markers has always been something that has lingered throughout the Dead Space series. We know what the Markers do which is reanimate necrotic flesh in twisted forms and that it can also contain any necromorph outbreak. It is also know that the way the Marker affects people is different from person to person some see codes others are driven insane and often experience hallucinations of dead loved ones. The way in which the two major powers in the Dead Space series react to the Marker shows a varied response and views on its purpose. Earthgov believes that by using the Marker they can unlock some type of new technology or energy source to meet the demands of a human population that has absorbed and depleted Earth's resources. Unitologists see the Marker as holy relic that offers away for humanity to trascend death and become immortal.
The reality is both groups don't really know who created the Marker or even why the Black Marker was on Earth to begin with. In the book Dead Space: Martyr, the truth behind the story of Michael Altman is revealed and we learn Unitology's true origins as a way to coverup the truth about the Black Marker and to make those who created the religion very wealthy and powerful.
But we also learn the Black Marker has been on Earth for millions of years and has been know to the locals of the region in which it was found for a very long time. The side effects of tampering with the Marker are obvious, people become hyper-psychotic and violent which leads them to kill themselves or others. Once they are dead their bodies are transformed into Necromorphs who's sole purpose is to seek out and kill as many people as possible in order to create more Necromorphs. We know that a Necromorph outbreak can be contained by a Marker and that necrotic flesh reanimates in the presence of a Marker or Marker fragment, The lingering question for what is to come in Dead Space 3 is. What exactly was found on Tau Volantis and how does it relate to the Marker?
My opinion is that Earthgov recovered the original Marker after Altman sunk it and moved the research to Tau Volantis where they soon abandoned it, then it was found by miners years later. But whatever was found on Tau Volantis it is better that it remained buried and left alone. Afterall some mysteries are better left alone and forgotten than revealed. But it is clear whatever is there must be destroyed, if people are to survive.