If you aren’t sick to death of these, for “Earth is space Australia” please consider… the ocean.
Idk why but I’m super into the idea of humans going out and exploring the galaxy and becoming well-known interstellar travelers where Google Maps now has a Google Universe page and we’ve digitally recreated entire planets so that humans who can’t or don’t want to leave Earth can explore them in VR… but we still haven’t explored more than like a quarter of the ocean floor
And like some plucky alien marine biologist from a planet where the water never gets deeper than like 2000 meters is planning to study on Earth because holy shit have you seen how much WATER they have?? And her human friend asks what she wants to study and she replies “Oh, well, I’ve heard the deepest place in your ocean is over five times deeper than it is here, I’d love to find out if anything can still survive under such pressure and so far from sunlight.” And their human friend looks at them in sort of distressed admiration - “What? Why are you looking at me like that?” - and is just like,
“Oh, things can survive alright. Freakish things from the depths of hell.” And that’s how plucky little alien sits up all the night eye getting steadily wider while their human friend shows them pictures of things like the viperfish and the pelican eel and the blue ringed octopus and oh did I mention we’ve barely explored a fraction of the ocean so like we know there used to be this prehistoric shark that grew up to 20 feet long and was one of the biggest predators of all time but honestly “used to be” is an optimistic statement because that thing could still be lurking in the depths of the ocean and we just don’t know
Alternatively, hostile alien species arrives and claims our oceans because we aren’t using them, leaves screaming within a week