Most of the instructions are clear. However:
-- The Turn One and Turn Two etc. terminology is confusing, since you also refer to the player's turn. Consider changing this to "Step One" etc. in the headers.
-- It looks like doing a Corporate Action is required -- you should note this, much as you note that the Erosion and Corporate Bases steps are optional.
-- The second step of the FLOOD action refers to "the lowest adjacency". This is jargon and a bit hard to understand. Consider unpacking this term and explaining the process in a little more detail -- a graphic would help a lot here.
-- In BUILD, it's not initially clear that you're adding to the top of your existing Production Biome, OR starting a new one if you have recently EXPANDed and have no Biome. Consider explaining this first, before describing the die roll and add process. Also, can you EXPAND one turn, FLOOD for one or several turns, and then BUILD? The phrase "pushed your Production Biome onto the planet on your last turn" doesn't account for this.
-- In the Erosion step, there are a lot of conditions as to what biomes you can and can't erode to. However, starting with where you can't erode to is confusing. Try stating the biomes that are qualified (biomes adjacent to the original biome that have fewer tiles in them than the original biome, right?), then clarify the statement with the examples of biomes that are not qualified. A couple of bulleted lists or an example graphic might help a lot here.
-- "Cascading erosion" seems like a critical step in the process, and probably should get its own paragraph rather than being called out with an "IMPORTANT!" (which is usually applied to exceptions or clarifications).
-- Can you erode to an empty spot on the table, effectively creating a new biome? I'm thinking no, but this should be explicit.
-- The Corporate Bases step will be easier to follow if you talk about the eligible locations first. Start by summarizing the basic procedure ("You can place or move 1 base per turn."), then describe where you can place the bases. ("You can put a base on any biome that is empty, stable, not flooding, and not adjacent to two bases belonging to another player.") Having defined that, you can then describing and moving -- including the assurance that the moved base does not have to be adjacent to its previous position -- and then do the step of removing other players' bases.
-- Can a corporate base be adjacent to the bases of two or more other players, each with one base? This should be explicitly stated either way.