Marduk is a planet sized device of destruction made by the alien race known as the Annunaki. The Annunaki were responsible for bringing intelligence to the planets Mars and Tiamat. After they destroyed each other in a war, the Annunaki brought intelligence to Earth.
After intelligence was brought to Earth they created Marduk. It was made with artificial intelligence of the Annunaki and was programmed to destroy civilizations before they could destroy themselves. In it's history, Earth was once a extremely technological society prior to today. But their warring habits caused the retribution of Marduk, who destroyed the race. The current population of Earth rose from this calamity.
When Marduk was found to be approaching Earth once again to stop it from it's own destruction, the being known as Ayaman enlisted the Silver Surfer, among others, to try to rescue the life on Earth. Unable to stop Marduk, they instead tried to save life aboard the Great Ark and rebuild after Marduk wreaked it''s havoc upon the Earth. They planned to raise children to be advanced and peaceful so that the threat of Marduk would never some again.
But it was soon forseen by Ayaman that the Earth would be destroyed by Marduk in it's entirety. They instead chose the planet Sof to rebuild the human race. But eventually, the Silver Surfer could not leave the Earth to it's destruction. He tried to stop Marduk and even united his Power Cosmic with the planet in an effort to save it. He also learned that Marduk was the one who was behind the Silver Surfer's orders, which enraged him further. Unfortunately, the Surfer's power was not enough, and he failed.
It was then that Ayaman revealed to Ellie Waters that she was an essential part of the universe. Marduk was only a manifestation of man's fears and not truly real. Ellie used her powers to recreate the Earth as it was before, and Marduk was erased from existence.