Confused about Earth vs. earth? You’re Not Alone!

Eart from outerpaceMy last blog dealt with word use that many — including me — find confusing: different from vs. different than and compared to vs. compared with.

Here’s another word puzzle I’d like to solve. After spending considerable time online trying to understand when to capitalize Earth and when to use a lowercase e, I’m still not sure. Here’s what I found.

Earth vs. earth

When you are referring to our planet as part of the solar system, it generally is capitalized, as are other celestial bodies: Jupiter, Pluto, Venus, Mars, Earth, etc.

How far is Earth from Mars?
Of all the planets in our solar system, only Earth appears to support intelligent life.
Astronaut Scott Kelly returned to Earth March 10 after a full year in space.

When referring to soil or to phrases that are not technical or related to astronomy, avoid capitalizing earth:

What on earth are you talking about?
I’d go to the ends of the earth for my granddaughter.
An avid gardener, he loves the smell of damp earth in his hands.

Unfortunately, I think it can be difficult to determine when a reference to the earth is based in its being considered a part of the solar system. These examples from my online search are not considered grammatically wrong:

When the sun and moon are at opposites sides of the earth, we see a full moon.
Scientific research has helped us estimate the earth’s age.
Concerns about carbon emissions have raised awareness of changes in the earth’s atmosphere.

Despite comparing multiple sources, I have to admit that I’m still not certain I understand when to use a capital E and when to us a lower-case e for our Earth/earth.

In efforts to be consistent, I will continue to follow The Associated Press Stylebook guidelines related to word use and punctuation. It states:

Generally lowercase; capitalize when used as the proper name of the planet. She is down-to-earth. How does the pattern apply to Mars, Jupiter, Earth, the sun and the moon? The Astronauts returned to Earth. He hopes to move heaven and earth.

Note that AP suggests “generally lowercase.” When I’m uncertain about whether to capitalize or not to capitalize, I plan to stick to lowercase earth.

If you have insights or opinions about Earth vs. earth, I’d love to hear from you.

And please let me know if there are words that stump you when it comes to capitalizing. I have a list, and I’ll add yours to it for future blog topics.

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Addendum July 2018
A reader shared with me this guideline from the Chicago Manual of Style:

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.

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Kathy Watson

Kathy Watson has a love/hate relationship with grammar; she loves words and the punctuation that helps them make sense, yet she hates those pesky rules. A self-proclaimed ruthless editor, she prefers standard usage guidelines of The Associated Press Stylebook. Her easy-to-use Grammar for People Who Hate Rules helps people write and speak with authority and confidence. She encourages and welcomes questions and comments. (Email)