#evolution?

the culture of the grounders in the 100 confuses me. i wouldve thought that it would take a heck of a lot of time for such a hugely different culture to arise from the science-based one that the ark people have. like we know that they had to survive without science when the nuclear apocalypse happened but did a whole new religion have to develop as a consequence of this? and how would their religion and rituals and such develop after such a short time that is only 97 years? in the show the grounders refer to beca as an ancient god but it hasnt even been a whole century since beca came back to earth? and even then they showed people in hazmat suits and not grounder-like outfits surrounding her when beca arrived? does it really take such a short time for a huge new religion to replace science in its entirety? i would like someone to help me understand this