Daily Reminder DC Comics is a fusion of 8 different companies each of which got there own earth at one point.

National Comics-Earth 1
Detective Comics-Earth-0
All-American Comics-Earth 2
Quality Comics-Earth 10
Entertaining Comics- Earth 39
Charlton Comics- Earth 4
Fawcett Comics-Earth 5
Wildstorm- Earth-50

And dont forget, the Modern DCU is a fusion of Seven Earths

Earth Two
Earth One
Earth Four
Earth S
Earth Quality
Earth M
Milestone Universe
"Vertigo Universe"

This is the Endosymbiosis, the same way Transformers absorbed GoBots, Christianity absorbed holidays from pagan religions, Roman Myth was built from countless local traditions, and the Caribbean developed its syncretic beliefs such as Voodoun and Santeria DC has become a modern hodgepodge of countless narratives.