Maybe “the arrival” could also be the origin of Element? Aliens that seeded Earth with the stuff, hoping it would terraform the place into a planet sized mine for them to use.
Lo and behold, for some weird reason humans are still alive and kicking. “Oh hey, there’s this weird Rockwell entity we can use to actually complete the terraforming process...”
This is just a half assed theory from my still waking up brain, but honestly I’d be okay with if they never explain where Element really came from beyond “outer space stuff”. Some things just don’t need explaining.