Who is this mysterious hero? Why is he called Earth Man? Can we even call him a hero when his quest/mission seems to be simply beating someone who doesn't like him to a salvage goal? Let's look and see...
A-ha! He's got a rocket ship. Maybe this isn't Earth, but an Earth-like planet and he's a visitor from our world? That could explain the Earth Man name...
Nope - they're heading through the "core of the Earth" so not a different planet.
Maybe that's where the name comes from - he can burrow through Earth with his ship? His power is digging holes?
But, wait! A hint of power appears...
...with zero connection to the name Earth Man. That was his one and only appearance. I guess nobody else could figure out what he was supposed to be, either. If you're going to do a hero named Earth Man, have a reason for the name. That's not too tricky, is it? It's not like i'm asking the impossible here.
Actually, the Impossible would work just fine, and make more sense. Since the name is in use by some Kirby-Come-Latelee, just pretend Hugh Mann chose the name Earth Man instead of Impossible Man in this tale and see if it doesn't seem more appropriate than the usage above (art by Bernard Baily? (contested)) -
page art from Supersnipe v2#8 and Meteor #1 (1945)
