A Galactic Fairy Tale

Once upon a time, a very long time ago, there was a galaxy belonging to a large galactic group with a furious galactic center. It was devoid of all life and compared to the billions of other galaxies in the universe that were teeming with life, it was a dead galaxy which made it extremely rare to the point of being one of kind.

It came to be that a very large comet impacted on a moon (about the size of the moon of earth) orbiting a near-earth sized planet and sent almost half of the moon's mass out into space. In a very short amount of time, (approximately one month to 100 years) this debris coalesced into a ring consisting of billions of objects ranging from the size of a grain of sand up to the size of a small car. This moon-ring was beautifully lit by that solar system's star and was amazingly unique in the entire universe.

Over the next several million years, small meteors and tiny comets of ice ran through the moon-ring and were either captured in the ring or smashed through it making it down to the surface of the moon. Each icy comet that made it to the surface of the moon melted due to powerful pulses of radiation emitted from the moon's undulating nickel/iron core.

It took only a few million years for the water to begin to create an ocean that covered approximately half of the moon's surface. It was the first ocean on any moon.

In the subsequent years to follow, after several millennia, a massive dark and dusty asteroid arrived into the moon's galaxy and began a long journey of nearly 120,000 light years traveling deeper and deeper in towards the center of the galaxy. Along its way, the asteroid entered the star system that contained the moon and the planet it orbited. Due to the massive gravity of the asteroid and its trajectory, the asteroid caused the moon to be ejected from its orbit and it was thrown out into interstellar space becoming a rogue moon.

After the moon traveled nearly 4 billion light years, it entered the Milky Way galaxy. Soon after entering the galaxy, this moon's path led it into a star system with an average sized star and 8 orbiting planets. After an uninterrupted and uneventful journey, the moon collided with the third planet in an average solar system in an amazing impact blowing nearly 20% of the planet's mass out into space.
This ejected matter was quickly captured by the gravity of the remains of the planet and began to orbit around it in an irregular manner. In an extremely short period of time (in as little as month) the ejecta aggregated then coalesced into an entirely new moon.

The remnants of the rogue moon that remained in the planet were of a completely different nature from the planet's original matter. As the two types of elements commingled, a huge virus, one that had been delivered in the composition of the rogue moon, so large that it could almost be seen with the naked eye, became energized by the star in this solar system.

For the next several million years, the virus remained dormant. At an undetermined time, after  slowly storing energy--the virus morphed and transformed through several stages of  development until it gained the ability to reproduce and begin consuming inanimate matter for supplemental energy. From this process, an atmosphere was formed and started to be filled with monomers which began to produce simple organic compounds. These simple compounds transformed into ever more complex molecules that accumulated along the ocean shores and in thermal vents.

Through a long and complicated process, life had been introduced to this once dead galaxy. After many billions of years, life spread from solar system to solar system until the galaxy became like all of the other galaxies in the universe; a galaxy full of every imaginable form of life.

Short version of the story:

There was a galaxy devoid of life.
In that galaxy, a comet collided with a moon ejecting 20% of the planet into space.
It formed a moon-ring.
Meteors and comets passed through the moon-ring.
They melted on the moon and created an ocean.
A dark asteroid arrived in the galaxy.
It nudged the moon out into interstellar space.
It became a rogue moon.
The moon entered the Milky Way galaxy.
It collided with a planet.
The rogue moon brought a virus to the planet.
The debris of the collision coalesced into a new moon that began to orbit that planet.
The virus transformed into the primordial soup of life.
Life came to be in the once dead galaxy making it like all the other galaxies in the universe.