A world that changes under their feet
The sea in this project's universes is not a fixed line on the map. It rises and falls on a slow cycle, and because land is simply "ground above the waterline", a moving waterline quietly redraws the coastline, the shallows, and what can be walked on - without a single rule ever telling an organism that any of this is happening.
One line of arithmetic, and no stored state
The waterline at any moment is the base sea level plus a sine wave in the tick number. That is the whole mechanic. It keeps no state, so there is nothing about it to checkpoint and nothing to include in the world's state hash: any tick's sea level can be recomputed from the tick alone, forever, which is what keeps the world replayable.
In Universe 1 the amplitude is 0.11 elevation units around a base of 0.3,
so the waterline travels between 0.19 and 0.41. That total swing of
0.22 is four of the discrete ground units organisms excavate and deposit - enough to
put a shallow cell under water, or take one out from under it. The cycle takes 1,209,600 ticks,
which at this world's pace is on the order of eleven thousand simulated days. Genesis happened at
the base level, where the sine is zero.
Every land-or-water decision in the simulation reads that same moving value. Nothing special is done for coastlines: a cell is land when its ground stands above the current waterline, and the coastline is simply wherever that stops being true this tick.
What an organism is told about it: nothing
There is no tide channel, no clock, no forecast, and no sense of the sea as an object. An organism perceives the same generic local quantities it always does - what is under it, what is around it, how deep the water is at the cells it can sense. A falling sea is not announced; it simply means that a cell which was water last time an organism passed is ground now.
So any use of the cycle has to be built out of ordinary perception and ordinary behaviour. Nothing rewards noticing it, and nothing in the genome encodes it. See what an organism actually senses.
Two kinds of offshore land, and only one of them is patient
The map has land out in the water, and it was deliberately built in two varieties that differ in one specific way.
The islets are small domes connected to the coast by a shoal - a submerged ridge
lying one tenth of an elevation unit below the base waterline, with its floor at 0.20.
The sea's low point is 0.19. The shoal therefore clears the water near the bottom of
the cycle, by a hundredth of a unit: for part of every cycle there is a walkable path out to the
islets, and an organism that happens to be in the right place at the right time can simply cross.
The islets carry twice the resource capacity of ordinary land, so there is something real out
there to find.
The offshore summit is different, and the difference is exact. Its pass lies
0.16 below the base waterline - a floor of 0.14, which is deeper than the
sea ever falls. The waterline bottoms out at 0.19 and the pass stays submerged through
every low in the life of this universe. No amount of waiting opens it.
The only remaining route is to fill the water in: excavate ground somewhere, carry it, deposit it, and repeat until a causeway stands above the waterline. That is the same conserved-substrate mechanic described in reshaping the world, applied to a problem nothing was told to solve.
The arrangement is deliberate: one prize reachable by patience, one reachable only by building. But nothing selects for reaching either. There is no build action, no construction objective, no reward for a causeway, and no channel that says "there is land over there". The map was arranged so that the possibility exists. Whether evolution ever finds it is exactly the open question, and stating it as an expectation would be the mistake this whole project is arranged to avoid.
What to look for
Over long spans, the interesting places are the edges: cells that change between ground and water as the cycle turns, the shoals that connect and disconnect, and whether anything accumulates where the sea has been retreating. A shoreline that has moved from where it started can mean two very different things - the sea moved, or something moved the ground - and telling those apart by eye is not always possible from a single look.
Watch the live world · how organisms move ground · the live universe's frozen law set