Evolution of Early Planets

I think it’s a good idea to bring this thread back up as discussion surrounding environmental tolerance adaptations mature a bit. It would be beneficial to have a shared understanding of how the player’s planet on an average playthrough will develop, as the player’s environment will have a dramatic influence on progression and other mechanics. I think a good amount of theory is present throughout the forums and this thread in particular, so I won’t dive too much into background information as I tend to do.

I will disclose that I am interpreting an average, “normal” setting of a Thrivian planet to largely reflect Earth’s geological history with some deviations. We can discuss variation when we better understand environmental tolerances, the “normal” playthrough, and when planet generation stops being cursed as a feature.

The Evolution of Compounds

Let’s first think of this topic through compounds, which represent the resources and niches a player has available. Looking at Earth’s history, the various compounds included have a generally predictable pattern influenced by natural developments on a planet.


  • Iron – Iron can be very prevalent on an early planet, but could slowly become less and less common as oxygen is introduced to the environment. Eventually, iron will likely be limited to the depths of the ocean.
  • Hydrogen Sulfide – Hydrogen sulfide will likely share a similar story with iron – predominance over most biomes, then gradual reduction with the introduction of oxygen. Hydrogen sulfide would probably be the most important compound in the beginning parts of the Microbial Stage.
  • Glucose - Glucose already changes through a playthrough, reducing throughout time as a representation of reduced free-floating organics.
  • Phosphate – Phosphate could probably reduce a decent amount as more and more organisms show up and utilize free floating organics, but not to the same extent as glucose. Local events, such as runoffs, volcanic activity, and more can temporarily increase the concentration of phosphate within local conditions.
  • Ammonia – Similar to phosphate, ammonia could reduce a decent amount as more and more organisms show up and utilize free floating organics, but not to the same dramatic extent as glucose. Local events, such as runoffs and volcanic activity, can temporarily increase the concentration of ammonia within local conditions.


Oxygen – The most dramatic example of an atmosphere evolving, oxygen will introduce itself to the planet through the biological activity of photosynthetic life. It might be beneficial if oxygen cannot dip beneath a certain concentration if it reaches certain checkpoints. For example, once oxygen reaches 3% on the surface, it cannot go below 3% no matter what, it cannot go beneath 6% once it reaches it, 9%, etc. This will ensure that the game doesn’t crap out and destroy the playthrough since it is so important for advanced morphologies.

Oxygen will first be largely limited to the surface patches, but will make its way down to the deepest parts of the ocean around early multicellular (ocean depths became oxygenated relatively recently).

  • Nitrogen – Nitrogen likely was present at a lower level than what is now seen on Earth. The maturation of the nitrogen cycle as well as the evolution of plate tectonics has resulted in an increase in available nitrogen, until it reached modern levels.
  • Carbon Dioxide – Carbon dioxide was likely more present on a young Earth than it was now. It is believed that carbon dioxide lowered somewhat as time went on, though obviously not to an extreme extent.
  • Sunlight – The atmosphere was rather hazy on young Earth due to the presence of methane and ammonia, volcanism, and the lowered rate of oxidation due to, well, a lack of oxygen. The beginning of a playthrough can have slightly less sunlight available on average, but this can trend towards normal conditions rather quickly. The early level of available sunlight can be an environmental factor that varies a lot from playthrough to playthrough.
  • Temperature – The oceans were much warmer on a young Earth, though this period of heated waters didn’t last very long – otherwise, a lot of Earth’s water might have evaporated and have been lost through a weak atmosphere.
  • Salinity – Earth’s oceans were likely less salty at first. Considering the lack of variety on salinity in the Microbial Stage in Thrive, I think it would be fair not to have salinity vary immensely throughout a playthrough.
  • Pressure – Pressure shouldn’t dramatically alter itself throughout a playthrough, though different planet generation settings can have average depth be a tweakable factor.

As a Whole, How Will The Climate Evolve?

I think that we should have environmental compounds be rather unstable and volatile to a dramatic extent at the beginning of a playthrough for multiple reasons…

  • Young planets don’t have stable biogeochemical processes established.
  • Introducing variations in the early game can be a relatively easy way to increase replayability. Players might have to rapidly pivot evolutionary strategies, which would be easier to do considering the simplicity of the organisms at this stage of the game.
  • The lack of other complex organisms results in a lack of a notable threat in the beginning of the game, so the environment should probably serve that role at first.

Currently, I think the average playthrough will follow this cadence…

  • Hectic, Chaotic Beginnings – The beginning of a planet’s history is characterized by unstable biogeochemical processes and intense natural events, such as bombardment and volcanic activity. Compounds will fluctuate dramatically with little rhyme or reason, and atmospheric concentrations will similarly vary. The environment as a whole is a threat to be paid attention to. To reduce the burden of this fluctuation on new players, hydrothermal vents can reduce less extreme swings in concentrations, and would generally be sheltered from the most severe of environmental events. These might be the first 10 or so turns in the average playthrough where compounds could genuinely go from being extremely prevalent to incredibly sparse within a patch.
  • Initial Stability and Slight Increase of Oxygen – Compounds fluctuations will eventually slow down into more settled numbers with some variety, and the frequency of environmental events will reduce. This is where we can start seeing some of the compounds trends mentioned above. Oxygen will start to build up near the surface, introducing hints of the most powerful respiration strategy in Thrive and allowing players to begin adding some complexity. This will help players feel secure enough to start somewhat specializing around their niche, allowing them to build up to performing endosymbiosis. Compounds might still fluctuate, but not to the dramatic extents seen before.
  • Snowball Earth(s), the Upsetter – Glaciation events can serve as an immense challenge placed on the player, reducing the viability of photosynthesis, shaking up food webs, and forcing players and AI to adapt their morphology. We would probably want to introduce controls to have it so that oxygen can’t just disappear completely once it shows up to not completely screw over the player, but the rate of oxygen production will likely slow down for a certain amount of time. Snowball events can occur multiple times, though we might want to consider making it so that later snowball events are less harsh than earlier snowball events.
  • Oxygenation and Stability – Eventually, oxygen is introduced and the atmosphere and environmental concentrations generally settle around certain levels. This will allow players to develop strong eukaryotic capabilities and eventually attempt to become multicellular. Environmental events may still happen, but to less of an extreme.

I think what this cadence will ultimately stress is the role of oxygen in relation to progression. Since oxygen has the most powerful form of respiration in the game, it is likely that that most players will trend towards adopting oxygenation respiration as a strategy. This is okay since the vast majority of complex, multicellular life as we know it is dependent on oxygen. But having oxygen also have a strong impact on the atmosphere will also provide a sort of rhythm for the player to understand; when oxygen arrives, compounds start shifting dramatically. Therefore, variation in gameplay can be tied to the nature of how oxygen is introduced.


Great that someone put this to writing. It would be great if we could get some input from our @Theory team about this.