Earth, earth

When it is mentioned together with the capitalized names of other planets or stars, “Earth” is generally capitalized and used without the definite article “the.”

• When will the first colonists leave Earth to settle on Mars?
• Alpha Centauri is over 4 light years away from Earth.

In other contexts, references to our planet do not require a capital.

• The earth revolves around the sun.

• Why on earth does she want that job?

References to the soil, adjectival uses (e.g. “earth sciences”) and combined forms (e.g. “earthworm”) also remain in lower case.

• Kenneth enjoyed gardening because the warm earth smelled of summer.
• Sarah is a genuine earth mother, caring for every living creature she encounters.
• Some anglers prefer earthworms as bait; others insist on minnows.
• Alia’s fear of flying kept her earthbound.