Earth – la tierra
(Pronounced tee-eh-rah)
To remember that earth is pronounced tee-eh-rah (tierra) in Spanish, use the following mnemonic:
The Earth shed tears over the errors (tierra) humans were making.

Earth is feminine, so it's la tierra. Imagine a lady spinning the Earth on her finger.

Examples of tierra (earth) in a sentence
La tierra gira alrededor del sol cada 365 días.
(The Earth orbits the sun every 365 days.)
Los científicos estudian la tierra para entender su origen.
(Scientists study the Earth to understand its origin.)
El astronauta vio la tierra desde el espacio.
(The astronaut saw the Earth from space.)