The correct answers are Earthlings, who need oxygen to survive, are surprisingly fragile. and The planet, which is mostly covered in water, looks blue from space.

Both correct options properly use non-defining relative clauses with commas to add extra, non-essential information.

The humans, that drink coffee... is incorrect. You can never use the relative pronoun "that" immediately after a comma in a non-defining relative clause.

The sun that provides them with light... is incorrect. Because Earth only has one sun, "the sun" is a unique noun. Unique nouns require non-defining relative clauses (with commas and "which"). Writing it without commas implies Earth has multiple suns and we are specifying which one!