tommus wrote:"Als je de aarde vanuit de ruimte bekijkt, besef je dat die klein en kwetsbaar is."
If you look at the Earth from space, you realise that it is small and vulnerable.
Question: Could it also be written with "het" instead of "die"? ("... besef je dat het klein en kwetsbaar is.")
Note that the die in your sentence is actually a demonstrative pronoun; a demonstrative pronoun for common gender things that are further away. (Put that down!, celui-là). The sentence literally says "you realise that that is small and vulnerable".
You translated the Dutch sentence into English using "it" - a personal pronoun - because that's what's idiomatic in English. But "die" is not really a personal pronoun. See Wikibooks: Using demonstrative pronouns instead of personal pronouns.
Wikibooks wrote:Using die avoids the issue, ... Increasingly, personal pronouns are reserved for reference to persons (natural gender as in English). To refer to things people resort to substituting the demonstratives.
And both your dies would be that demonstrative pronoun die:
tommus wrote:"Als je de aarde vanuit de ruimte bekijkt, besef je dat die klein en kwetsbaar is. Die is ook blauw en mooi."