What’s so bad about Earth, you might ask? Let’s go through some of the basics of world-building and see how Earth stacks up. I’ll start from Earth’s strong points and work down to the really iffy stuff.
OK, to give Earth her due, the geography is fairly believable. There is a serviceable mix of terrains, from tropical jungles to barren deserts. There are a number of continents, nearly all well-inhabited. Navigable rivers provide means of access to inland regions and a location for believable large settlements.
As for some small criticisms: the mountain ranges in southern Asia and the western half of North America are a bit too large and stretch credulity, though nothing fatal. The southern half of the Pacific Ocean is nearly devoid of land; it should either have a bit added or perhaps the whole of the map could be shrunken down to compensate. Also, though not strictly a geographic issue, the fauna of Australia is a bit over the top (a more skilled world-builder would have used a lighter touch when making things poisonous).
I’ll put weather under geography as well. Earth’s weather is ill-explained. I think the world-builder should have gone to a bit more effort to make certain aspects of how it works more transparent to the reader.
Sometimes, when creating a world, you can have too much of a good thing. Culture on Earth is a great example. While a skilled world-builder would include a handful of distinct cultures, possibly even a dozen or more if they have the time and a pressing reason to include them in the story, Earth is overflowing with them. Cultures on Earth and being added, merged, consumed, sub-divided and redefined at such a pace that finding a touchstone to use in a story is difficult. Individual members of a given culture are just as likely to rebel against norms or adopt their own personal take on beliefs as they are to adhere to them. This lack of homogeneity can muddy seemingly simple characterizations of large groups.
A clever writer might take the opportunity to turn a stereotype on its head, but that trope has already been beaten, dragged and left for dead just by the world’s own backstory. Earth is already bursting at the seams with upside-down stereotypes and characters written against type. Most writers will find a better contrast in their story by hammering down this stubborn nails or just ignoring the outliers entirely, for the sake of simplicity (protagonist, and possibly antagonist, aside). This however is where we really start taking the dark road into customizing Earth into a working setting, rather than using it as it is.
The physics of Earth might appear to be one of its strongest elements. There are equations and laws and all the other good things you need to back it up. It’s believable, internally consistent, and can be used to explain most of the technology that Earth possesses. If the creator of the world had left it at that, it probably would have been fine. However, as with cultures, the builder went overboard. There are sub-branches of physics that involve a lot of hand-waving and technobabble, unresolved paradoxes and ill-explained phenomena. To cite a recent example, “dark matter” and “dark energy” seem out of place given the gravitas imparted to the Newtonian core of the discipline. It almost seems as if another builder took an existing work and slapped some extras in when the old physics started seeming stale. The same goes for the smaller and smaller particles that scientists are always discovering.
A hint for writers: Avoid power creep! You don’t always have to be introducing newer, bigger, better. I think the general readership was happy when electrons were the smallest particle; they were well-modeled so that even casual readers could picture them (plus, molecules looked great as cover art!).
The metaphysics of Earth, quite frankly, are appalling. For a decidedly low-magic world, there are more purported forms of magic and mysticism than one treatise could do justice. Psychic powers, tarot cards, wishing on stars, ghosts, placebos, crystal power, Ouija boards, transubstantiation, homeopathy, reincarnation, numerology, astrology, aura reading, exorcism and countless other beliefs both ancient and modern. Many are tied to the overabundance of cultures previously mentioned, others to the ill-refined scientific disciplines that are scattered across the world. Some seem to have bits of truth to them, but they are overwhelmed in the noise of shoddy magical systems slapped together according to the builder’s schizophrenic whim.
The use of any of these magic systems in serious fantasy needs to be done with the utmost care, often with significant disregard for the actual practice of that magic as written by the world-builder(s). Most often, successful fantasy that attempts to use Earth as a setting scraps the whole lot of them and starts from scratch. Faced with the daunting task of building a compelling magic system from the ground up, a prospective writer is still better off than they would be using the guaranteed train-wreck of canonical Earthly magic.
For all Earth’s failings as a setting, this is the most tragic. Given all the myriad cultures and religions to choose from, the world-builder needed only to select the most compelling of these. Earth, Heaven, Hell – it would have been enough, given a proper backstory. Alas, no. Instead of delving into the magical side of the universe’s origins, the world-builder went for a strictly scientific explanation, one that was wholly illogical from a story-telling perspective.
First, the universe just poofs into existence in one big bang. After that (somehow) it becomes infinitely large. Instead of using manageable but vast numbers, the age of the universe pulls out “billions” of years, something no reader can truly wrap their mind around. Combined with the limitations of its own physics, this infinitely large universe might as well have been a few planets huddled about a single sun. The rest could have been mere decoration in the heavens since it is impossible to reach other suns and the planets that surround them. It’s simply wasted work to create entire galaxies that are unreachable by the defined technology.
The latter might have been forgivable if the magic system allowed for some substitute for the Earth’s technological failings. Of course, with magic that can, at best, occasionally make a statue cry or facilitate a dubious conversation with a dead relative, interstellar teleportation would fall flat for lack of believability.
As for deities, the world seems to, by and large, agree that one is a pretty good number. Multiple religions use the same one with different names and rules, and there are a few other major pantheons as well. However, as largely non-interventionist deities, there are limited opportunities for pitting the followers of god against another. Without clear mandates and fantastical powers, divinely granted, religious wars have no place in an Earthly setting.
Earth is a bloated, low-magic world with too much backstory and not enough compelling characters. A writer who feels compelled to set their fantasy there is best served by a steamroller and a supertanker filled with corrective fluid; there’s changes that need to be made.
If you are going to tell a tale, tell it in a world all your own. There are bits and pieces of Earth that might serve as inspiration. Use those myriad cultures and beliefs like a spice rack, choosing a bit here and there to flavor a world so that people recognize the taste of it. Don’t let it overpower the meal though.