Earth-54 is an alternate universe, first described in Crisis on Infinite Earths: The Compendium. The planet Earth in this universe is technologically advanced in various scientifical fields; Tommy Tomorrow landed on Mars in 1960, as an example. "Mars-54" was covered in canals, supported lush jungles, and held the fossilized remains of long-dead dinosaur-like animals.
In the universe of Earth-54, Earth's moon has an atmosphere (but one that is poisonous to humans) and supports plant life that gives off toxic pollen. Humanoid aliens once lived on the moon and left a time capsule that was discovered by Tomorrow in 1967.
Venus is inhabited by a strange fauna and flora, and rains every 5 hours. Judging by the American flag planted on Venus by Tommy Tomorrow, the United States of Earth-54 had not conferred statehood on Alaska and Hawaii by his time.
The element 99 was only discovered in 1988 and, if sprayed on the atmosphere, it would protect the humanity from a Nova.  (In Real World, this element is Einsteinium, which was discovered in 1952.)
Crisis on Infinite Earths: The Compendium stated that the following comics were appearances of Earth-54:
- Crisis on Infinite Earths: The Compendium lists entire issues rather than specific stories as being Earth-54 stories so it cannot be determined if stories that don't contradict larger continuity told in those issues happened on Earth-54 or the Earth being depicted at that time.
- No trivia.
- Characters from Earth-54
- Other things related to Earth-54
- Earth-54's Comic Appearances
- Reality Gallery: Earth-54
Links and References