!!!⚠️Spoilers to Steven Universe⚠️!!!
Earth was not chosen to be a new planet in the empire.
The Diamonds were aware their fuel source was finite, and curious to see if there were better uses of the materials planets were made of
So they decided to put together a research team who went to Earth.
On this team were a select few gems chosen for powers that would be useful in experiments.
A Ruby and average Amethyst were brought for their strength.
A Bismuth was brought for her building and shape shifting.
A Lapis Lazuli was brought for her terraforming and water manipulation.
A Sapphire for her foresight.
A Peridot for her technical prowess.
And at the head of the team was Pink Diamond and her Pearl.
Why was Pink Diamond chosen?
Because the other diamonds were busy and obviously a diamond should lead the team.
Lapis, Ruby, Bismuth and Amethyst went to the surface to collect a variety of materials and brought them back to them moon where they began experimenting.
Pink was on a call with the other diamonds when experiment went terribly wrong.
There was a volatile explosion that poofed Bismuth and Lapis, and damaged Amethyst in a way that would leave her as the Amethyst we know in the show.
Pink Diamond called the other Diamonds back, telling them what happened and that these experiments were dangerous.
They told her to keep working.
So she and the remaining gems went back down to the planet to gather more materials when they finally got a better look around.
There was life.
They explored for a bit before rushing back to the moon base, and reporting their findings to the reformed and recovered gems.
Pink urged them to explore the planet, they were a science team after all.
What kind of team would they be if they didn't look around?
So together the explored and roamed the surface, each falling in love with planet in some way.
Pink stopped.
"We can do this. We can't hurt this place."
Silence.
Then Pearl spoke up.
"You're right. Plus these experiments are too dangerous."
Pink would call the Diamonds again, even meet with them in person, but they ignored her concerns.
After a meeting with the team they decided to fake all of their deaths.
Pink Diamond, Sapphire and Pearl worked together on fake gem shards, Peridot hacked the tech, and the rest worked on explosives so they could fake their death.
When the day came, Pink called the Diamonds to update them on the experiments, giving them one last chance to change their minds while the others made noise to make it sound like an experiment was in progress.
Blue and Yellow didn't change their minds so Pink gave the other gems the signal.
Pearl and Sapphire screamed, Pink quickly looked over to them, feigning horror and rushed off screen.
Bismuth let off an explosive so a loud boom would be heard and seen and Peridot triggered a bit of code that made the camera feed glitch and sound warp before cutting it to static and terminating the call.
Blue and Yellow frantically called back.
They hadn't thought of that.
Acting quickly Lapis chucked an explosive at the intercom.
No one could call them now.
Now they just had to set up the station to look like what it sounded like.
Time skip
The place looked like a mess.
The last thing to do was set a bomb on a delayed timer and warp down to earth.
Time skip
Years had passed, and a ship was headed towards Earth.
Spinel was on that ship, sulking at the prospect of heading to the planet that had killed her Diamond, but things had to be done for the sake of the Empire.
Little did she know that Pink Diamond lived on, along with the rest of her research team.
She was reasonably angry when she saw them alive, learning that Steven was Pink and how all that mourning for nothing.
She grew to understand the beauty of Earth, and so would the other Diamonds when they came around.
