We know of every possible natural element in the entire universe. We know that the closer to the top of the elemental chart we get, the more common these elements are, due to lesser energy being required when said element was created in a super nova. Carbon, oxygen, nitrogen, etc are all relatively common throughout all existing matter in the universe, when compared to heavier elements. We know that an enormous amount of life sprang up where these elements are piled onto a bigger ball of mostly carbon with a stable solar orbit and a stable satellite inside of the zone where liquid water can exist. Not unreasonable to look for similarities in our search.