Or the earth.
Or sometimes just plain earth.
In many cases, identifying whether the word should be treated as a proper or common noun is a cinch, but there are also plenty of times it could go either way, and an editorial decision is required.
The AP Stylebook‘s terse entry gives us some general guidelines: “Generally lowercase; capitalize when used as the proper name of the planet.” This hints at two broad editorial strokes we can make that will cover a large number of uses of the word — though perhaps not quite as many as it seems:
- When it’s synonymous with soil or dirt, earth is a common, uncapitalized noun.
- In astronomical and astrological texts, in which the name of the planet is included among other planets and celestial bodies, Earth is a proper, capitalized noun.
So to decide whether the word you want is earth or Earth, you first should decide whether the word is being used as the name of the planet, but that’s not always easy to figure out. What on earth could I possibly mean by that? I mean that there are plenty of set phrases, like “what on earth,” that are unclear. Is the earth in “what on earth” in opposition to heaven, i.e., the sky vs. the ground. Or is that Earth in “what on Earth” in opposition to other planets?
Garner’s Modern American Usage, Third Edition, offers us a bit more: “In reference to the planet we live on, earth is usually preceded by the and is not capitalized. … when Earth is referred to as a proper noun, it is capitalized and usually stands alone.”
This gives us another marker to help decide: the definite article. According to Garner, if earth is preceded by the, we know to leave it as a common noun, even when the word is naming our planet. This is helps us through a number of idioms — “the superlativest noun on the face of the earth,” for example, or “the four corners of the earth.” But that still leaves plenty of gray area, and as copyeditors, we also have the power to remove that definite article when it interrupts the flow of the text. Compare, for example, “the hardest substance on the earth” and “the greatest showman on earth.” Should the article be removed from the first example, or added to the second? Should either earths be capitalized?
The Chicago Manual of Style (17th edition, at 8.140) goes a bit further: “In nontechnical contexts, the word earth, in the sense of our planet, is usually lowercased when preceded by the or in such idioms as ‘down to earth’ or ‘move heaven and earth.’ When used as the proper name of our planet, especially in context with other planets, it is capitalized and the is usually omitted.”
The consensus seems to be, then, that lowercase earth, and especially the earth, acts as sort of the default option in general texts, and that the capitalized Earth makes an appearance only in special cases. That’s a good, defensible editorial position to take, especially if you find yourself, as I have, stymied by the arguments for and against capitalization and your deadline is hurtling toward you like a falling meteorite.
But those “special cases”? Notice that the CMoS guidance is specifically for nontechnical contexts. In the same way that style choices for religious terms can be influenced by whether the manuscript is intended for a general or specifically religious audience, your style choice for earth may change based on what your manuscript is. Is it for a general audience? Lowercased earth will probably be more prevalent. Are you dealing with an astronomical or astrological text or space-based science fiction? Uppercase Earth might prevail.
Notice that the word usually appears a total of four times in the Garner and CMoS excerpts. Therein lie choices — the kind of choices copyeditors are paid to make. Sometimes that’s what it comes down to, your choice as an editor. But as long as you can justify your choice and you use it consistently, your editing will be great.
Out of this world, even.