Are There Aliens in the Universe?

i think we can be pretty safe in assuming that there are not actually, like, a people sized organisms that are walking around unnoticed on earth and are aliens of some kind. But i wanted to explore a maybe more plausible, still unproven, but more interesting, sort of parallel idea. The article is called a shadow bio sphere. Now, by a shadow biosphere, she means a rarely considered form of alternative life, not aliens from another planet, but aliens from earth. It's possible they're here right now and we simply can't see them. They could possibly include different amino acids to build their proteins. Or any other means by which the chemistry of early earth could have bined