*Spoilers* The marker is the necromorph's kryptonite apparently. When it was in the planet, it was keeping them from fleeing. Then they removed it, and the necromorphs were able to roam about and hijack a shuttle to the ship. At least that's what was said in the movie..
Seems easy, but confusing when skittles are flying at your face. -zxcvb2588
yes but one more thing, this red marker is man made and the planet was a test site for what exactly?, also if the marker was suppose to stop the necromorphs, why did it make people kill themselves for the recombinant dna to infect the corpses
The red marker was man-made, but the black marker that it was based on was of alien origin.
Now the Black Marker contained the formula for the Necromorph cells, and was worked on by Dr Ahlman (sp?) who used what he'd been able to learn from the black marker to found Unitology. This is the major religion in the Dead Space setting, and most key members of the crew were members of the church of scient- sorry, Unitology.
The government however, fired Ahlman and continued to work on the black marker, leading to the creation of the Red Marker. They also discovered what the Necromorph cells did around about this time. In order to escape scrutiny from oversight committees, this research effort was done on Aegis 7 (IE, the planet in the game) and the Necromorphs took over the facility, but not before one of the scientists had a vision on how to create an amplifier that would boost the dormancy signals that the Markers emit. This amplifier is the pedestal that you have to put the marker on at the end.
Now several decades later, a new colony on Aegis 7 finds the red marker, and believes that it's another Alien Marker like the first (since nobody but the government knows about the original research facility) so they send the Ishimura, which has been carefully seeded with church members to take the marker and return it to earth. Unfortunately, removing the Red Marker from the pedestal awakens the dormant necromorphs.
The Red Marker (and presumably the Black Marker as well) emit a mixture of gamma and beta waves and sonic signals which give people a mixture of headaches, visions, hallucinations and psychopathy. It was this effect, coupled with the Church's principles being based on wrongly translated parts of the original markers text (something about if you use Necromorph cells you will be reborn after death.) is what caused most of the problems.
MY THEORY: The marker wasn't a guide to immortality like the Church of Unitology believed, it was in fact a warning on what NOT to do to find immortality. The makers of the marker created it to warn others not to make the same mistakes as they did.