Seems to me that the primordial religion, if it could be called that, is a form of paganism that has pantheism, animism and shamanism. Also, it may contain sun worship.
In this 'religion', they felt a connection w the land, had respect for nature and the animals. They often explained or apologised to the animals that they had to kill for food. This form was practiced around the globe, on all continents and islands. Is this the true religion? Or, does it make more sense that later, more developed, what could be called proper religions are more correct? Which form is more compatible w science?
Good summary by Satanus.
I would offer that the origional religion of humanity had prevailing themes of recognition of the duality of the universe. Man/Female, Yin/Yang, Hot/Cold, Light/Dark.
What these ancient people knew, was that achieving balance between these two dualities resulted in LIFE. A good thing!!
This is what they worshiped...LIFE.