Today, let's talk about some of the fundamentals of the Drewniverse. One thing I feel that's never really adequately explained in the DC setting is "Why Is Earth So Special?" I mean, yes, most of the stories happen on Earth starring Earthlings because that's where and for whom the comics are actually written, but in universe there's very little curiosity as to why the heck there are so many superpowered beings from this world and others running around.
I mean, in Marvel you have the idea of the Celestials, godlike beings who are responsible for the sheer number of mutants running around due to their past genetic manipulation. (It's probably no surprise, but I was one of the five people who read Earth X all the way through to its finale in Paradise X.) So whenever a seemingly normal human developed some weird technology, you could just say, "err, yeah, they were a mutant or something" and just get on with it. In DC? Not so much.
Do we really need a reason why the focus of the universe is on Earth? For the casual reader, I don't think we do. They don't care so long as Batman punches the Joker and that's totally fine. The stereotypical casual reader would be put off by long metaphysical text dumps about the vastness of space and some ancient godling who blah blah blah. You know, I'm "kind of a comics nerd" and I don't want to read that stuff either. I enjoy the concepts, sure, but really want to be shown, not told.
On the other hand, it is setting stuff like this that rewards the long term reader and hopefully keeps them coming back for more. Think about Lost where viewers were falling over themselves because they felt there was some sort of bigger logic they didn't see lurking beneath the surface. This is the sort of stuff that provides fodder for long-form watercooler talk. I think it is in the best interests of the genre to encourage readers to wonder, "Hey, so Poison Ivy and Swamp Thing both have plant powers, what happens if they cross paths?"
Furthermore, it's just cleaner to have all this stuff set up behind the curtain in advance of rolling out a new universe. One of the reasons comic continuities, and DC especially, need so many reboots is that originally the characters were not supposed to be hanging out together. Superman lived in his own world where Metropolis took the place of New York City, Batman lived in his own where Gotham was there instead. Once characters began to crossover into other titles, you ended up with disparate worldviews that needed to be resolved. So you end up Metropolis, New York City, AND Gotham all crammed into the same general area. Which is fine, provided you don't think about it too hard, but given that people who think about your comics buy your comics, you probably want to put some work into the foundations of your setting.
So with that in mind, let's get back to our question, "Why Is Earth So Special?" Why do intergalactic badasses like Brainiac or Darkseid even care about Earth? I mean, even if their most hated enemy Superman is hanging out there, surely there's the rest of the universe where he's not. Go conquer that and worry about Supes later. But no, like a crusader slouching towards Jerusalem, the baddies time and again keep coming back to Earth. Where did the Rannians first aim the Zeta Beam? Earth. Abin Sur crashed on? Earth. Jor-El aimed his kid at? Earth. Earth. Earth.
Clearly, there's something about our blue marble, something that is lacking on other worlds. What? Well, two things to start:
The Red and The Green.
In the DC Universe, The Green is a concept developed by Alan Moore for Swamp-Thing. It's a sort of connection that exists between all plants on Earth. The Red is a similar thing, except for animals. Both consist of fields that surround the planet that certain people/beings can tap in to, whether intentionally or by accident, as a source of their powers. Swamp Thing, Poison Ivy, and so on for the plant-based Green and Animal Man and Vixen for the animal-centric Red, just to name a few.
In the Drewniverse, Earth is unique for not only having a well developed Red and Green, but for having both together being well developed. Think about the alien landscapes presented in most comics. Sure, you have weird flora and fauna, but there's not a whole lot of variety to them. If there is a purple tree with pink flowers on Planet X, then all the trees on Planet X are purple and pink. All small lizards look alike on Planet Y. This is largely because artists are not insane and don't have the time or wherewithal to make a fully functioning ecosystem. Meanwhile, in panels depicting a park in Metropolis, it's easy to pick out several types of trees and birds.
It is the variety of species of plants and animals on Earth that have allowed the Green and Red to evolve to levels not normally seen anywhere else in the universe. The Green, being significantly older than the Red, has even evolved to the point of a sort of demi-sentience. The Red's development is accelerating as well, especially since the rise of man, Earth's most devious animal. There is a sort of Cold War conflict between the Green and Red and this rivalry spurs on new developments. On other worlds, it's common for a comparatively few number of species to fight it out and become dominant (think about the pre-history of Krypton presenting in Doomsday's backstory), which in turn stunts the growth of their Reds and Greens.
Life calls to life, so on a fundamental level, even life from other worlds and ecosystems would rather be on Earth. Pin it on their selfish genes, but whatever it is, there is a sort of instinctual pull to the planet. Most are not even aware of the affect the Red and the Green have on them - they just know that they want to be here. This is why big names like Darkseid or Trigon just can't get Earth out of their minds, even though for them to possess Earth would mean the destruction of the fields that drew them here in the first place.
Even artificial intelligences like Brainiac are drawn to Earth like vermin looking for scraps. Heck, maybe there are other, similar fields out there for them. It would be interesting to explore the birth of a third field for mechanical or artificial life. Call it The Grey or The Blue and have it slowly emerging on Earth due to the rise of technology. How would the established fields react to the emergence of a third on an already crowded planet?