I'm getting to that, but yes. You are correct. A little over 5000 years ago, Gems came to the planet Earth and began to establish a colony there. From what I understand from the reports, it was a promising site... But rebellion broke out, and eventually the plans to develop the planet had to be abandoned.

So, instead, the Diamonds decided to put the Earth to a different use, and authorized the establishment of several experiments to be left there to develop over the years. Mostly these were comprised of various fusion experiments, which were left to incubate below the Earth's surface.