Does Aliens Exist On Earth?

If there is other life out there I think that the possibilities of aliens existing of earth would be quite good. Due to curiosity of how life on Earth has come about, how "Earthlings" do things differently and such wonders.

Yes because i watch a video on discovery chanel that in achene times [ i forgot  how to spell it] they show writing about it . [ i forget what century ] that aliens invade earth before the bc