Sci-fi ecosystems- the last two novels

This is my fifth blog entry. It will focus on two novels by Hal Clement- Close to Critical and Cycle of Fire. Both feature planets with extreme climatic conditions. The former novel takes place on a planet with several times Earthly gravity and atmospheric pressure, and 370-degree heat (close to the critical point of water, hence the title). An Earth-made robot is on the surface learning about the environment and the intelligent natives. The latter novel occurs on a planet which orbits a binary star, and because of this has cycles of hot and cool periods occuring every quarter-century or so. The life forms of the hot period grow out of the dead bodies of the cool period creatures, and vice versa. Additionally, all life can regenerate lost body parts and so is rarely fully killed until the climate changes.
Close to Critical features several harsh conditions besides the temperature and pressure. Very little light enters the atmosphere, so even midday appears as dark as Earthly midnight. To deal with this, the native fauna have eye structures that look like spines rather than Earthly eyes (which would be near-worthless in such conditions) and presumably use light in a different way. Additionally, the atmosphere and most of the surface fluids are partly sulfuric acid, so the plants and animals need to be able to withstand that. Finally, each night, the temperature difference is enough to turn water vapor in the atmosphere liquid. The resulting raindrops are gigantic (yards across) and drift any which way in the air (which itself is so near the liquid state that the drops hardly fall at all. Any creature enveloped in a drop is knocked out, so all the organisms can tolerate asphyxiation during the night by eliminating most bodily processes requiring air. As for the variety of species and their relationships, there are various plants and herbivores, as well as carnivores of various sizes. One predator is called a “floater” and drifts through the air like a jellyfish in water, killing prey with poisonous tentacles. Although the ecosystem, and especially the relationships within it, is not fully fleshed out (hardly any small animals are listed), most creatures seem to have some adaptation to the immense pressure on them- for example, most of the plants are brittle, while others just lie on the ground, but are still hard enough to avoid caving in.
In Cycle of Fire, the environmental difficulties are different. The heat changes are accompanied by an acidification of the atmosphere and liquid water in the hot phase. There are no creatures able to live in both periods, but the spores of some organisms can withstand the changes. In time, these spores were taken into the bodies of other species active in the other period, and the two species developed a symbiosis. As the changes begin, the old organisms die off and those of another species emerge from their flesh. However, these new ones already possess the spores of the “parent” species. The ecosystems present in each period conform to the general rules governing Earthly ones, and have a large number of species. However, most of these species are recently evolved from a few forms which survived the catastrophe in which the binary system was formed- the surviving forms differentiated very rapidly, while the numerous types whose spores could not cope went extinct. Thus, this novel, like the former one, present the idea that the defining characteristic of life-forms and ecosystems is the way they cope with environmental conditions.


  1. cmbetti says:

    This is really interesting about how detailed the author planned out the environment and the ecosystem. Your mentioned the air in Close to Critical. Does the author mention what type of gas the air is made of? Also, does the environment play a large role in these stories plot, or is in the background?

  2. Sorry to not reply to this for so long. I haven’t been on here lately. There are several gases in Tenebra’s air, of which oxygen and sulfuric acid are the most prominent in the story. The environment in the Hal Clement novels drives the entire plot, while in many of the other books, it is only a background player.