I don't know how people though naruto series was originally about ninjas but get real for once , the very first episode started with telling how an alien fox with 9tails attacked a villiage so in the entire series, their physical chakra ,tailed beasts and jutsus are nothing earthly ,

They all get those from the divine tree which isnt even from the planet earth ,the sage of six path's might have born on earth but hes still alien so evenfrom the beginning the series involved aliens if you considered the tailed beasts still a fraction of the ten tails which is the divine tree