Question

"Earth is unique". Theoretically, we should use "the Earth" but sometimes I saw only "Earth" used. When should use "the Earth" and when just "Earth"?

Answer 1

Basically if you say "Earth" you mean the planet where we live but if you add the article the as in "The Earth" you refer to the soil.

By saying "The Earth" you are being so specific at refering to this planet. In conclusion the context is what made us the right answer or a mistake.

Answer 2

Before the word "article" in the question.