While translating the ancient language of the Sumerians, Sitchin discovered that a race of aliens called "The Anunnaki" had come to Earth to mine gold. There were different reasons why they needed gold ("It helped prolong their lifespan"."It prevented the atmosphere of their home planet from deteriorating", etc., etc.).
The mining started about 450,000 years ago. The original miners were the Anunnaki themselves and after thousands of years, they wearied of this tedious work and wanted a break.
In order to quell a rebellion of the Anunnaki gold miners, the leaders created a hybrid race between themselves and primitive man. These were human slaves who continued to work in the gold mines.
Millions of souls were placed in these bodies and they would work until the flesh rotted off them. Earth was a prison planet and many advanced cultures were sending the souls of their planets' criminals, crazies and misfits here.
The so-called bosses of Earth were actually super criminals who had engaged in warfare and electronic repression against free spirits. This was first disclosed on Earth in "Interview With An Alien".
I also wrote a blog on how Jesus Christ undid many of these evil works (i.e. "Three Hours of Darkness"). "As in Adam all die, so in Christ shall all be made alive". There was a master plan behind making Earth a prison planet.
There are still many aliens around who treat mankind with less respect than an insect. Their fate could be like "The Husnock" in the Star Trek NG episode, "The Survivors".