Tidemark

Tidemark has no land. Not a single rock breaks its surface above the waterline — the crust is geologically young and has not yet thrust plate mountains high enough to emerge. What it has instead are ecosystems of extraordinary complexity, built over nearly two billion years of uninterrupted aquatic evolution. Bioluminescent fields of colonial organisms stretch for hundreds of kilometers in the deep. Predatory creatures the size of ocean liners drift through mid-level thermals. Nothing yet has climbed toward sapience — but the neural architecture of several species is growing more complex each geological age.

The amber glow of Aethon looks different from beneath Tidemark's surface — filtered through kilometers of water into a deep, dim gold. The creatures that live at depth have never experienced direct starlight. Some of the larger colonial organisms have been observed reorienting in response to Aethon's gravitational pull during solar transits — the closest thing to "looking at the sun" that life on Tidemark has developed.