The ecology of Epona obviously depends crucially on the long-term cycles in the climate described above. To illustrate how, we might speculate over the fate of life during one complete cycle.
Imagine the last warm spell. In ten million years the ecology of Epona has recovered to become almost as complex as on Earth. Land and marine biota are in a state of climax - production by plants is balanced by consumption by animal and decay organisms. Then, with the waning of outgassing, the CO2 deficit becomes felt, the planet starts to freeze, glaciating high to mid latitudes, and bulldozing away land-based life. What's worse is that eventually CO2 falls to the extent that photosynthesis on what land remains ice-free becomes very difficult. Ecosystems begin to unravel, consumption outstrips production, and when excess biomass has gone we are left with a very impoverished biota. Most members of the previous ecosystems are extinct, what remains is a tundra-like landscape with sparse soil amongst eroded rocks - a desert where one might think a desert ought not to be - supporting a scum of sparse life recycling its scarce raw materials in tight and intimate cycles.
The seas and their edges are different. Carbon
dioxide is buffered in the waters by the presence of abundant carbonate
sediments and the fact that organisms that live in the rich mud on the sea
bottom consume and recycle carbon and other nutrients very efficiently.
Photosynthesis in the upper waters thus goes on almost as well as it has ever
done and, like on Earth, turnover of plant matter is very rapid supporting a
large animal biomass. Epona during these times is like a global Antarctica -
little life on land, except on the shoreline, but plenty in the sea.
A hundred million years after the retreat of complex life into the sea, the next volcanic episode brings on a new warm spell. The ice falls back and abundant CO2 is now present to support photosynthesis and biomass production. Vast and almost lifeless land surfaces are exposed- vacant ecological niches aplenty for a veritable evolutionary eruption! This is the sort of biosphere from which we evolved our biota and sophont! We had a wild, roller-coaster, ten million years of explosive evolution to populate the land with plants and animals designed for marine, or semi-marine life. (Note that on Earth, after the Cretaceous mass extinction, the first epoch of the Cenozoic, the Paleocene, which was 10.1 million years long, witnessed a rapid diversification of mammals into the vacant niches left by the dinosaurs.) Just like with the aftermath of a mass extinction or the opening of new land, contingency (chance) reigns supreme. The merest fluke might select one clade for dominance in the new niches and doom another. This gave us the greatest choice for design one can imagine - a Burgess shale style radiation, followed by decimation of diversity and the choice of just a few body plans on which to build all that is to come.
Every 100 million years the die is cast anew and a fresh group of creatures gets a shot at a brief dominance on land. If a sophont evolves in time before disaster, then perhaps technology might prolong Epona's final Summer.
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