How Did Isaac Destroy the Marker in Dead Space?

The Marker Isaac Clarke actually destroys is the Site 12 Marker at the end of Dead Space 2. The apparition of Nicole tries to get him to die so the Marker can finish Convergence. He refuses, fights her inside his own mind, and wakes to find the Marker dead and crumbling. In the first game, original and remake, he doesn't destroy Marker 3A at all: he puts it back on its pedestal. (Dead Space; Dead Space (2023); Dead Space 2)

Dead Space (2008): he puts it back#

In the first game, the scientist Terrence Kyne convinces Isaac that the outbreak will end if Marker 3A goes back on its pedestal on Aegis VII, where it held the Necromorph Hive Mind in check. Isaac flies it down, carries it past the wrecked dig site and sets it in place. It lets out a pulse and the Hive Mind goes quiet. (Dead Space)

Then Kendra takes it off the pedestal again to deliver to EarthGov, and shows Isaac that Nicole had been dead all along. The Hive Mind rises and kills Kendra. Isaac kills the Hive Mind and escapes by shuttle as the slab of crust the Ishimura had torn loose falls back onto the planet. (Dead Space)

Marker 3A is wrecked when that debris comes down, but not completely. In the animated film Dead Space: Aftermath, EarthGov sends the USG O'Bannon to Aegis VII to collect its pieces. (Dead Space; Dead Space: Aftermath)

What the pulse did to Isaac matters more. Dead Space 2 reveals that it planted the full blueprints for a Marker in his head. (Dead Space 2)

Dead Space (2023): same ending, one extra#

The remake keeps the same story and the same main ending: Marker back on the pedestal, Kendra killed by the Hive Mind, Isaac escaping. The difference is who is with him. On the planet, Kendra reveals that the woman he'd been working beside wasn't Nicole but the botanist Elizabeth Cross, who was under the Marker's spell too, and Kendra shoots her. (Dead Space (2023))

The remake's New Game Plus adds a secret ending if Isaac collects all twelve Marker fragments. Instead of the jump scare, the shuttle is covered in Marker symbols and a deranged Isaac calmly tells the Nicole hallucination he has to build something first. That points straight at Dead Space 2. (Dead Space (2023))

Dead Space 2: he destroys the Site 12 Marker#

Three years later, EarthGov has used the blueprints in Isaac's mind to grow the giant Site 12 Marker on Titan Station. When the Necromorphs gather around it, Convergence begins. (Dead Space 2)

The Nicole hallucination tells Isaac he has to make them whole. He uses the Noonlight machine, the device EarthGov used to pull the blueprints out of him, to open up the Marker-touched part of his brain, then makes his way to the foot of the Marker. There "Nicole" shows what she wanted all along: for Isaac to die so the Marker can absorb its creator and complete Convergence. (Dead Space 2)

He refuses. The fight moves inside his own mind, where he shoots the apparition among shadowy figures. Destroying her destroys the part of his brain the Marker still held. When Isaac comes round, the real Marker is dead and falling apart. (Dead Space 2)

He doesn't blow it up with a weapon, then. He takes away what it needed from him. Ellie Langford picks him up as the station's reactors go critical, and Titan Station and the Marker's remains are destroyed together. (Dead Space 2)

Dead Space 3: a moon, not a Marker#

Dead Space 3 is a different kind of ending. On Tau Volantis, Isaac and John Carver restart the alien Machine that froze the planet, which drags down the incomplete Brother Moon hidden there. The Awakened add-on shows the rest of the Brethren Moons already at Earth, and Isaac's fate is left open. (Dead Space 3; Dead Space 3: Awakened)

Read more: the Site 12 Marker, Marker 3A and the Dead Space 2 story explained. (Dead Space; Dead Space 2)