how many Infinity Gems must earths heroes seek out? 
Marvel Super Heroes In War of the Gems:  In the game's plot, Adam Warlock calls upon Earth's greatest superheroes to seek out the Infinity Gems before they fall into the wrong hands. Infinity Gems: The Infinity Gems, originally referred to as Soul Gems, are six immensely powerful fictional gems appearing in American comic books published by Marvel Comics.
six