The amount of carbon dioxide taken from the atmosphere depends on the amount of water that is being evaporated from the seas, because one needs water to make carbonic acid. An early Epona receiving less sunlight will have less evaporation, which means less rainfall. Less rainfall means more CO2 molecules left in the atmosphere and we all know what more CO2 means: greenhouse effect. A good quantity of CO2 equals a warm and equitable habitat for life. As Taranis grew brighter with time, the amount of evaporation on Epona increased, making more rainfall and taking greater quantities of CO2 from Epona’s atmosphere. With less greenhouse effect over time, the climate maintained fairly even in temperature—until a few eons ago.
Kill tectonism, and the production of carbon dioxide stops entirely. In a few tens of millions of years, much of the available CO2 becomes chemically bound to Epona’s crust. Freeze time.
At the beginning of the new low carbon dioxide era for Epona, some 1.7 billion years ago, her previously equitable climate eroded into the cold clasp of a prolonged ice age—despite Taranis’s increasing luminosity. For the land-based biomes, and a little less so the aquatic realm, the sustained ice age proved a significant challenge, causing vast extinctions. The very limited CO2 during this period was not enough to sustain photosynthesis very well for terrestrial plants, and they died. Herbivores quickly followed the vegetation’s death march, and the carnivores consequently suffered. In the oceans, photosynthetic organisms were able to survive by using bicarbonate as their carbon source, sustaining an aquatic biome, albeit a cold one.
Epona’s internal heat has not completely dissipated. Enough warmth has remained to produce residual bouts of terminal volcanism every one hundred million years or so, give or take an epoch or two. These huge plagues of eruptive activity release vast quantities of CO2 back into the atmosphere, providing a new greenhouse effect and an initially abundant carbon source for photosynthesizing life.
Under this warming trend, the ice retreats, and land areas previously covered in glacial ice become exposed for repatriation by life. The volcanism spike is short-lived, say a few million years, and the warm periods only last ten to twenty million years. Long enough for terrestrial life to radiate and become established, only to be choked from the continents as the C02 steadily drops, allowing Epona to ice over yet again.
Epona has experienced at least twenty of these glacial events in the last 1.7 billion years, and is at a warm period’s end right now, in our mod-ern era. Much new aerial, terrestrial and aquatic life has evolved during this most recent ten million years of equitable clime.
Much is known about the Tir fo Thuinn region of Epona, an ancient, flat, tectonically dead continental craton that has been weathered by rainfall and glacial action for at least one billion years. Due to space constraints, we’ll only look at the primary microfauna, megafauna and megaflora of Tir fo Thuinn. A very detailed aquatic realm, one terrestrial animal class, and at least two kingdoms of photosynthetic metazoans are being left out. The organisms described below are a world-wide presence, however, so Tir fo Thuinn provides a good opportunity to show some of what lives in the Eponan countryside.
Figure Three: Modern Epona. Many of the names for the large landforms follow a Gaelic tradition. Tir fo Thuinn, meaning “land under the waves” is also called the Sunken Continent. Tiene Eilean (Fire Island) is the most recent addition to Epona’s landmasses, having been produced by Epona’s latest convective bulging (not unlike the Tharsis region on Mars) and sudden bout of atmosphere warming volcanics beginning some ten million years ago. Large plumes of ejecta still billow from Tiene Eilean’s massive 10 km high volcanoes about every century or so.
Kingdom Archaeanimalia contains those Eponan animals possessing a somewhat Earth-like morphology and physiology, namely the silacopods, springcrocs and the flectocellids. Nevertheless, do not let these words fool you into thinking that mammals and reptiles are running around on the surface of Epona. Quite the contrary. Though the archaeanimalia have some similarities to Earth critters, such as internal mineralized skeletons in the case of springcrocs and external skeletons in the silacopods, there are no vertebrates, and members of the existing archaeanimalia classes are quite different from anything existing on the Earth.
Silacopods are a class of segmented organisms ranging from ant to gazelle in height—Epona’s lighter gravity seems to be aiding the larger forms. Silacopod bodies are supported and protected by an exoskeleton of silicon dioxide, basically glass. Respiring through solid silica is difficult, so the stem species had a pair of breathing stalks, which resemble antennae, on each of its ten segments. Being structured somewhat like a centipede, the basal species also had a pair of legs attached to each segment.
Figure Four: A nailbug, dread of the bare-footed walker. The tail, which is actually the reproductive organ, is shaped like the creature’s head, a mimicry which further aids the nailbug from predators by causing confusion. Not all carnivores are deterred by the spines and tricked by the tail, however, and one line of silacopod predators smashes the nailbug’s hard shells with limbs modified into heavy clubs.
All known silacopod species have evolved from the basal centipede form and are modifications of it: usually having fused many of the segments into three significant body parts and reducing the legs to four, two on some occasions. Thus, many of the critters appear to have an inordinate amount of antennae on each major segment, when in reality, these organs aid in respiration. Modification to the numerous limbs is common, with typical products being the creation of liquid-filled spines for sensing sound and grasping organs like those used by some arachnids and crustaceans on the Earth.
Silacopods have filled a variety of ecological positions throughout the terrestrial reaches of Epona, though the greatest variety of critters are found in the tropics of Tir fo Thuinn, and on an isolated chain of islands found far east of the continent’s mainland, called the Chirping Chain. Indeed, the Chirping Chain holds some of the most exotic species, including nailbugs, a herbivorous lineage that forms vast, ground-covering herds. Tall, sharp siliceous spines protrude from the back, making for a painful bed of nails for any soft-footed creature to walk upon.
Figure Five: The snapping flower commonly hangs from Epona’s vegetation, waiting for small flying critters to fly past, often avian pentapods. Like a chameleon firing its tongue, the snapping flower catapults its powerful clamlike jaws on a long, single leg, quickly plucking items from the air. Digestion is slow, with fluids filling the cavity made by the hard shells, not too unlike a Venus’s fly-trap.
The springcrocs are, well, weird. Looking somewhat like a singlelegged clam in their basic form, one would hardly guess that they rate amongst the most vicious predators on Epona. All springcrocs acquire food by hiding and then pouncing upon a hapless prey item that has wandered near. The leap is achieved by using the single, flexible and wellmuscled leg. Prey are usually killed with the springcroc’s clam-like jaws, though some use poison.