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Hi all. Several people have already noted that the existence of chull and other large arthropods requires Roshar to have more atmospheric oxygen than Earth does (if you want to brush up on arthropod respiration, start here: http://rspb.royalsocietypublishing.org/content/early/2010/03/04/rspb.2010.0001). However, it seems to me that Roshar's flora imposes additional atmospheric constraints. I have a theory which explains the following anomalies: 1: Rockbuds could not possibly be productive enough to support an ecosystem and a civilisation. 2: If crem is fertilizer, stormward waterbodies like Longbrow's Straits and the Steamwater ocean should have massive nitrogen and phosphate pollution, and should therefore be solid masses of algae. But Shallan's journey over Longbrow's Straits shows that this is not the case. 3: The atmosphere on the Horneater Peaks is different from, and healthier than, the atmosphere at lower elevations ("airsick lowlanders"). However, although temperatures on the peaks are similar to temperatures in the lowlands, agricultural productivity must be much lower--almost the entire population is devoted to food production, and the Horneaters are nevertheless still defined by having to eat parts of animals which other cultures shun. My solution to these problems is that Cultivation drains the Progression surge from the stormward waterbodies, and channels that Progression into terrestrial plants. Meanwhile, Honor (or, after his Shattering, some combination of his splinters and slivers) uses some combination of Adhesion (in its atmospheric pressure sense) and Gravitation to pull both oxygen and carbon dioxide towards sealevel. Thus, airsick lowlanders are suffering from both hyperoxia (too much oxygen, causing impired vision and seizures) and hypercapnia (too much carbon dioxide, causing a whole laundrylist of symptoms, including mental impairment (certainly the most common cause of the "airsick" comment) and irritability (contributing to their warlike culture)). A more detailed description is below. .......... First, photosynthesis on Roshar must be more efficient than it is on earth. Why? Well, it is obviously problematic that rockbuds and similar plants support the dietary needs of a reasonably densely populated nation like Alethkar. Rockbuds have to support their own relatively high metabolism (all that movement would mean that they would have to be at least as metabolically active as a sea urchin), and they produce energetically-expensive structures like shells. The drawings show that they have a relatively small leaf area to support all this. Obviously, some of these metbolic needs are met by crem, which seems to act as NPK fertilizer, but even massive fertilisation would only barely allow rockbuds to break even, much less support an ecosystem and a civilisation. How do I know? Well, let's use respiration as a proxy for metabolism. Each day, a sea urchin respires between 15 and 25 mmol O2 per gram dryweight (https://books.google.com/books?id=B322HrCUvNEC&pg=PA54&lpg=PA54&dq=sea+urchin+metabolism+calories page 51). Meanwhile, on earth, a perfectly fertilized leaf under perfect conditions produces at most 40 micromoles O2 per second per square meter (http://www.saps.org.uk/saps-associates/browse-q-and-a/463-how-much-oxygen-does-a-houseplant-give-off-in-a-day ). Perform the necessary conversions, and we see that one gram drywieght of sea urchin would require 60 square centimeters of leaf to break even metabolically. Again, on earth, it would take absolutely ideal conditions for a rockbud to be able to support itself, much less grow. So, either rockbuds have access to more energy than earth-plants do, or they have access to more carbon dioxide, or both. First, energy. Maybe Roshar's sun is much brighter than Earth's. However, I've not seen any evidence of this, and skin cancer is never mentioned--it seems like skin cancer would be the chief cause of death on Roshar if this were the solution. So, maybe rockbuds use a more efficient pigment for photosynthesis than chlorophyll. But nope: When Shallan had her shipboard vision of her garden, her first impression was greenness, so we know that Roshar plants reflect green light just like earth-plants do, and thus almost certainly use chlorophyll. So if Roshar plants are getting extra energy, they're not getting it directly from their sun. However, one of Roshars two-and-a-half deities is Cultivation, who is closely linked to the Progression surge, which is closely tied to plant growth. Meanwhile, there are the Stormward oceans, which are well-fertilized with crem but strangely non-fertile. It makes sense that Cultivation is channelling Progression out of the oceans and onto land. This might or might not be sufficient to explain rockbud productivity, but it leaves Honor out of the loop, and it doesn't explain starving Horneaters and airsick lowlanders. So, we give half the burden to Honor. Let's assume Roshar's original atmosphere was similar to earth's: 80% nitrogen, 18% oxygen, 300 parts per million carbon dioxide. Honor uses Adhesion and/or Gravitation to Bind both oxygen and carbon dioxide downward. The upper atmosphere is now almost entirely nitrogen, the Horneater Peaks are still similar to Earth, and sealevel is something like 40% oxygen and a full 5 percent carbon dioxide, enough to induce symptoms. Chulls frolic in the high-oxygen environment, plants have much more CO2 to work with, and lowlanders get airsick. Meanwhile, without the elevated CO2 concentrations, agriculture on the Horneater Peaks suffers. This unnatural distribution of gasses might cause Roshar to appear to have an entirely-nitrogen atmosphere from a distance, explaining WoB that astronomers wouldn't think Roshar is habitable. Of course, this theory is significantly weakened if there are superlarge arthropods on the horneater peaks--I think I remember Rock talking about eating Chull heads, but I don't remember if he ever said if Unkalaki chull were as large as lowland chull, or if they were much smaller. Lemme know whacha think. Much respect to all y'all from this first-timer, ecohansen