Second Eon, the First Age of Life: 4 Gigayears
The central mountains have been mostly worn away. Sea floor spreading has pushed the minor continent westward and subduction of ring plates has created an enormous crescent archipelago stretching from 45º north to 60º south. A large section of the supercontinent in the northeast has split off and made its way around the pole, smashing into the western shore and raising a large mountain range in the central north. A downward mantle convection current has created a depression near the eastern shoreline. A subcontinent impact has raised a small mountain range to the south of the depression. Every 262 days, the three moons align to create tides large enough to breach the dike and create a temporary sea in the depression, but only if it is summer in the northern hemisphere. This causes cycles of three to four years where the water level is continuously topped off, followed by six to seven years during which the sea completely dries out. Numerous such wet/dry cycles have deposited a thick layer of salt, creating the Great Salt Desert.
Another subcontinent impact has raised a mountain range on the western shore of the minor continent. The minor continent is surrounded by a ring of volcanic lagoons. During northern summer, these are all open to the sea. During northern winter, several of them are isolated, and the underwater mountain ranges restrict passage between the seas around the minor continent and the global ocean, except in surface waters.
Epimetheus rotates once every 20 Tellurian hours, giving it three atmospheric circulation cells per hemisphere. Average temperatures in the midtropics are around 30º Celsius, with a generally smooth gradient to 20ºC in the mid temperate zones. The enormous global ocean, broken only by diffuse island chains and the minor continent Antipode, allows storms to build up enormous power as they travel from east to west. Hypercanes routinely buffet the eastern shores of both continents, with the minor continent receiving mostly mid-level storms, while the supercontinent experiences a mixture of tropical storms, hurricanes, and hypercanes spawned off of the western coast.
Rainshadow Desert- A low mountain range runs along the eastern coastline just south of the Great Salt Desert. This blocks water-saturated air flowing in from the ocean, creating a wide swatch of desertified land angled to the north and intersecting the southwestern half of the Great Salt Desert. Occasional hypercanes are capable of breaching the mountain barrier and dumping large loads of water and organic debris picked up from the ocean and the eastern face of the mountains over the course of a day or so, but there is no other source of rainwater for the region, and daily temperatures range between -10ºC and 25ºC in the winter and 10ºC and 45ºC in the summer during years that the Great Salt Desert is dry, with reduced ranges during wet years.
Great Salt Desert- Northwest of the Rainshadow Desert, the Great Salt Desert is only a true desert in the southwest, where it intersects the Rainshadow Desert. Elsewhere, it does receive rain, but the only water fit to drink is that which hasn't yet hit the ground. All the rest is hypersaline. The borders of the desert are very loosely defined, but it is contained within a shallow depression formed by the downward flow of magma in the mantle below. The lunar cycles, combined with the changes in sea level with the seasons, create varying tides over a roughly ten-year cycle, periodically flooding the depression with seawater, and then allowing it to dry out, depositing a thick layer of salt on the floor. Even rivers flowing into the desert from outside quickly pick up large quantities of salt as they run over the saline ground.
Tropical Rainforests- The eastern face of the mountain range which creates the Rainshadow Desert and the coastal plains north of the Great Salt Desert are is subjected to frequent storms and nearly continuous rainfall, ending just below the mountain ridge, or to a distance of 300-400 kliks inland on the plains. Average yearly temperatures are around 30ºC.
Tropical Savanna- Beginning between 300 and 400 kliks from the coastline, except where it curves back around the Deserts, the savanna receives approximately 125 cm of rainfall annually, with average temperatures around 25ºC in the higher latitudes, climbing to 30ºC in the near equatorial latitudes. Rainfall is roughly evenly distributed in the near equatorial latitudes, which also have more rainfall during the years that the Great Salt Desert is flooded, but it becomes heavily biased towards summer in the higher latitudes, approaching the subtropics.
Temperate Forest-North of the Tropical Savannas, precipitation becomes regular throughout the year. Temperatures average 23ºC, with temperatures dropping as low as -10ºC in midwinter and getting as high as 30ºC in midsummer.
Saltmarsh- Overlapping the Tropical Savanna and Temperate Forest are Saltmarsh regions. These are coastal lands with elevations low enough that they are capable of being flooded by seawater during hurricanes or high tides. The water in Saltmarshes is generally brackish year round.
Mediterranean Desert- Stretching from about 1500 kliks inland from the eastern coast nearly to the western coast, and actually making it all the way there in the south, the Mediterranean Desert makes up most of the land area of the supercontinent. Rain clouds are completely dispersed by the time the winds make it past the Tropical Savannas, meaning that rain may only fall every few hundred years in most of the Mediterranean Desert. The western edge has its temperature regulated by the close proximity of the global ocean, but most of the desert experiences drastic temperature variations between day and night and over the course of the year. In the central regions, temperatures range between -15ºC at night to 40ºC during the day. Even dew does not form here, and most rivers dry up before traveling far enough inland, making underground springs the only source of water. To the north and south, the desert turns colder, with milder daily variations but more noticeable seasonal changes. To the northwest, cold air masses descending from the Boreal Plateau keep temperatures down to a yearly average of 22ºC, and kicks up massive dust storms which travel generally southeast. To the northeast, the Mediterranean Desert is bordered by temperate forest and grassland, and sub arctic tundra. The annual melting of the southern edges of the tundra feeds rivers that provide seasonal water to the northernmost regions of the Desert. To the south, the Mediterranean Desert is bordered by the temperate Australian forests.
Boreal Plateau- A subcontinent impact in the northwest of the supercontinent raised the globes highest mountain range, nearly twice as tall as Earth's Himalayas, and dropping of sharply into the arctic ocean to the north. An enormous plateau forms the heart of the range, where average yearly temperatures are only 10ºC, and air pressure is only .7 bars.
Boreal Rainforest- Tto the west of the Boreal Plateau is the plain that makes up most of the subcontinent. Water-heavy winds blowing to the northeast drop rain on the northwestern coast of the mainland, just beyond the Mediterranean Desert, and onto the large subcontinental peninsula. The nearly perpetual rainfall permits the growth of temperate to sub arctic rainforests. Warm ocean currents keep the southern regions from freezing over, but the northern edges get heavy sleet and snowfall during the winter. Average temperatures are around 15ºC, but may drop as low as -10ºC on the northern edges during winter.
Arctic Ice Cap- The northern icecap floats on open water, as no landmasses extend into the arctic circle. During the winter, nearly the entire arctic circle freezes over, lowering global sea levels, and trapping gasses emitted from underwater volcanoes beneath the pole. In particularly active years, gas pockets under the ice can rupture, creating miniature cryovolcanoes and fractures in the ice. During the summer, the icecap shrinks to a mere 15º circle, raising global sea levels and releasing trapped greenhouse gases that help warm the sub arctic tundra.
Antarctic Bulge- An enormous system of supervolcanoes has raised an Antarctic sub continent connected to the supercontinent. During the several month long winter night, the subcontinent freezes over, with the exception of patches of land around active geothermal vents, but as there is no continuous path around the pole for ocean water to circulate, warm waters flowing down the coast keep the climate temperate, and vast forests flourish during the perpetual sunlight of summer.
Ring Lagoons- Hundreds of small volcanic islands and shallow lagoons formed from volcanic calderas form a rough ring around the minor continent. Most of those directly to the west, however, were swept away by a subcontinent impact, leaving the highest concentration of islands in the east. The eastern islands are regularly bombarded by low- to medium-power hurricanes, but the western islands are generally shielded by the main bulk of the minor continent. Temperatures remain a balmy 22-28ºC year round.
Rainshadow Desert- The mountain range raised by the subcontinent impact has produced a Rainshadow Desert analogues to the Chilean desert on Earth. Humid air masses cross the continent from the east, and drop all of their water on the eastern face of the mountain range as they are forced upwards and cool. On the western face, the descending cool air masses create a high-pressure zone that prevents rain clouds from blowing in from the west. As the cool air descends, it is rapidly reheated, greatly reducing the percent humidity, and soaking up any moisture it can on its way out to sea, rather than allowing what little bits might be left over from the trip over the mountains to condense. Thus, there is never any dew in the Rainshadow Desert, and the only source of water is mountain streams. Average year round temperatures are about 35ºC.
Tropical Rainforest- The eastern face of the mountain range receives huge amounts of rain, permitting the growth of thick forests on the slopes and out to two hundred or so kilometers onto the plains. The average temperatures are around 30ºC.
Tropical Plains- From the edge of the Rainforest to the eastern coast are flat plains, which receive moderate amounts of rainfall, around 50 centimeters annually. These support patches of forest among wide-open prairies. Average temperatures are around 30ºC.
Saltmarsh- Overlapping the Tropical Plains, these coastal regions are at such low elevation that they are frequently flooded with seawater during storms or high tides. The water in Saltmarshes is generally brackish year-round.