Justice League of America #210 (DC, 1983 — Cover A)

Physicists Ray Palmer and David Dorman discover an "X-Element," a vital catalyst for all basic chemical reactions, which is about to decay, thus disrupting all natural activity on Earth. As the Atom, Ray summons the Justice League, which splits up into sub-teams to stave off worldwide catastrophe. Just as all seems lost, aliens called the Treasurers appear, offering to reverse the decay of the X-Element in return for specimens of Earth flora and fauna, including, unknown to the JLA, one human: a seemingly ordinary postal clerk named George Arthur Stuart.