Chances

Tiny lifeforms
Alien planet
Globally encompassing trench - ocean

Lifeforms, in their billions, fling themselves from wall to wall
Most drown
Some stick - spore
Parental husks fall and die
...Repeat

Evolution...
Some learn to fly - higher than the walls
Most fall
Others burn up in the atmosphere
One escapes...
Expulsion into space

Dreams of colonisation -
Filling the universe with seeds of life

Passing spaceship...
Splat! on windscreen...
...Dreams die