175.5 Million Years PE
500,000 years more have passed since we last checked in on the world of Serina, and environmental conditions have become increasingly harsh and unstable. Serina sits now directly on the Thermocene-Pangeacene boundary, a period marked by extreme volcanism, widespread desertification, and ocean anoxia, which will last through the next 2.5 million years.
The past few hundred thousands years have seen the formation of a huge mantle plume between Striata and Wahlteria. A massive series of flood basalt eruptions results, similar to the earlier Striatan traps event that kickstarted the Thermocene but now larger than anything seen so far in Serina's inhabited history. By the start of the Pangeacene - an epoch which, for most if its history will be characterized by the presence of one major super-continent on the moon and only a few smaller isolated landmasses - virtually the entirety of what remains of Striata will be buried up to three miles high under millions of cubic miles of magma.
The stronger eruptions resultant from the Wahlterian Traps, unlike the slower, more flowing eruptions from the earlier, sizable, but much less destructive Striatan traps, will periodically produce intense explosions and release huge amounts of dust and debris into the atmosphere. Following the largest eruptions, these atmospheric dust clouds have and will periodically continue to reach such concentrations that at times, they will become so dense as to block out the sun. The result, despite continued sky-rocketing carbon dioxide levels and uncontrolled global warming, is the appearance of major short-term cooling events. More than once, following particularly intense periods of volcanism lasting several thousand years or more, the north pole and all surrounding regions, including Borea and Polar Anciska, become locked in ice and devoid of plant or animal life. In some instances, these brief ice ages will last upwards of twenty thousand years - long enough for glaciers to form and even move towards the equator toward the northern most regions of the forming supercontinent. Several series of eruptions already experienced have been so large and powerful, and the quantity of dust they brought into the moon's atmosphere, that they have darkened the planet's sun in the northern hemisphere for months at a time. The aftermath of this, in conjunction with the complete extinction of terrestrial plant communities in far-northern regions, is the complete extinction of terrestrial ecosystems on any isolated landmasses north of the supercontinent. The ark of Polar Anciska and the isolated land of Borea are reduced to barren outcrops of stone.
All the while, in between the most extreme eruption periods uncontrolled greenhouse gases result in extreme periods of heating. As the eruptions release countless millions of tons of carbon dioxide, each period of intense cooling is eventually replaced by one of even greater stifling heat as soon as the dust settles out of the atmosphere. The carbon dioxide continues to enters the oceans, worsening their acidity. Over the long term, temperatures on Serina continue to rise, melting all newly-formed glaciation and ice caps from polar regions and causing catastrophic rise an fall of sea levels. Marine temperatures reach deadly levels numerous times at the Thermocene-Pangeacene boundary, as high as 120°F in shallow equatorial seas - temperatures absolutely lethal to all life except extremophile bacteria. With the seas virtually lifeless across much of Serina by this time, surviving sea life other than microbes isolated to the small forms of algae, fishes and invertebrates able to survive in sporadic pockets of oxygenated surface waters in habitable polar seas, there is little to move nutrients and dissolved gases through the water column. The oceans, already anoxic at deep levels, thus become almost completely devoid of oxygen as a result of extreme temperature spikes near the surface. The carbon influx is even more destructive now than before following the complete shutdown of photosynthesis in the northern hemisphere and most of the global seas, meaning that very little can now be sequestered out of the atmosphere.
During cold periods, life on Serina becomes uninhabitable anywhere north of the equator. Between them, temperatures all along the equator rise to more than 140 degrees Fahrenheit - fatally hot for almost all terrestrial life for prolonged periods. A 3 million years' long see-saw between between fire and ice wrack Serina's remaining remaining ecosystems to their cores in a period of intense climactic unrest that will come to be referred to alternately as Armageddon, where life must fight to survive what is seemingly the end of the world.
Serina's southern pole, the regions which once were the lower portions of Stevhlandea and Karri, is the least affected region throughout Armageddon, but the climate even here is unstable and harsh for higher life compared to anything the Thermocene had to offer. Conditions are as well extremely seasonal, ranging from subzero to more than 110 degrees F, with ice ages bringing respite from the worst summer heat but worsening winters and the intermittent hot periods producing milder winters but extreme summer highs. The northern half of the southern habitable belt is largely arid desert, but coastal regions support limited life through oceanic fog and summer storms that blow in from the sea. True forests are by this time restricted solely to a thin band along the southernmost edge of the new supercontinent, which now performs more than 95% of all photoynthesis occurring on the planet. Until the end of the volcanic period, it will be the only ecosystem on the entire moon which still serves to sequester carbon dioxide from the atmosphere. Almost everywhere else, photosynthetic communities have been totally broken down. The seas reach a level of stagnation not seen since the start of the Hypostecene, while land at the equator is reduced to barren, sun-scorched desert, virtually sterile of the kingdom of life and that at the poles reduced to nothing more than solid ice in the cold times and algae-encrusted bare rock in the hot ones. The almost total loss, globally, of photosynthesis results in a substantial decrease in atmospheric oxygen levels. This is exacerbated further by the proliferation of extremophile anaerobic bacteria which produce toxic hydrogen sulfide gas in the steaming equatorial oceans. Together, and coupled with extremely high concentrations of carbon dioxide and other greenhouse gases, such as methane released with the repeated thawing of polar ice caps, these events produce an atmosphere that could be considered downright toxic to a great majority of life. As if to kick the remaining life while it is already clearly down, the reduction of atmospheric oxygen results in a global thinning of the ozone layer, particularly along the equator but also near the south pole where the last land ecosystems cling precariously to life, allowing harmful radiation to reach the moon's surface and increasing the incidences of cancer and other deleterious mutations noticeably by the end of the era. Plants experienced a heightened rate of mutation, mostly negative, but persisted, offsetting high rates of radiation-induced infertility with even higher numbers of offspring, ensuring at least a few would survive. Remaining land animals were all but forced into nocturnal niches to avoid the harsh solar rays during the day time.
The Thermocene-Pangeacene boundary - a literal armageddon for life as we knew it - will go down as the most extreme, volatile, and simply devastating extinct event in the history of life as we know it - even more destructive than the Great Dying at the end of the Permian on Earth. More than 99% of life on Serina is obliterated over the course of three million years.
But the unrest would not last forever. The extreme south pole had provided a small but sustainable pocket of refuge for a limited pool of terrestrial and freshwater life, a small remnant population for sure, but one which contained among it a sampling of the varied tapestry of life which had evolved all across the world, each one having been pushed to the bottom of the world together as their isolated continents became one. Eventually, these continents would settle together and the magma plume would recede. As volcanism slowed, extreme climactic changes became milder. Freshwater released in enormous quantities from short-lived polar ice caps throughout the boundary period would begin to flow over the surface of the heavier and virtually stagnant saltwater, producing shallow rivers of pure, freshly oxygenated water down from polar regions toward the equator. Following the rivers would be the plants - algae from the northern islands, and a variety of flora from the southern refuge. Soon the sea would be overgrown with a carpet of green floating vegetation, floating on just this shallow layer of freshwater and spreading at a phenomenal rate. As they grew, they were sequestering the surplus of carbon dioxide from the atmosphere, releasing huge quantities of oxygen in its place. As they did so, temperatures cooled and rainfall returned to the equator. As soon as it did so, terrestrial grasslands and finally forest communities tentatively migrated back northwards from their final hold out in the south. Slowly, tentatively, but surely, life would recolonize the regions scraped clean at the end of the Thermocene.
The Pangeacene had arrived.