Imagine a world of infinite geology, a haphazard study in karsts, spiring peaks, vast spanning deserts, young seas filled with odd red life. It spreads on forever, stunningly diverse in all aspects save starkness.
It is alien, but only after the fashion of those times and places of our own world which remain alien to us.
Within these unending austere landscapes, wander myriad tribes of hominids. Not quite human, something less, perhaps something more.
Their world slowly fills with literal bile. Acrid and brilliant green, it consumes, breaks down, and winnows away.
This is not a metaphor. What do you do?