175 Million Years PE: The End of the Thermocene

We are now near the very end of the Thermocene epoch. The long period of relative warmth and stability Serina has so far experienced since the Cryocene is now beginning to change again as tectonic movements bring the most dramatic changes the moon's environments have seen in over one hundred million years.

above: Map of Serina 175 million years PE, at the very end of the Thermocene.

The Land

The continents of the east and west, separate for so long and evolving in splendid isolation, are now converging back together into a single landmass, with the long-isolated Kyran Islands having recently connected via land bridges to both Anciska and Wahlteria. As so many continental plates begin to collide, plates slide under one another and mountain ranges begin to rise. Rifts form, through which magma reaches the surface. Volcanism begins to increase once again toward the end of the Thermocene, flooding the atmosphere with carbon dioxide. The sudden build-up of uncontrolled greenhouse gas causes global temperatures to spike, even more than through the rest of the epoch. Equatorial regions become hotter, to the point that most water evaporates back into the atmosphere before ever falling as precipation. Reduced rainfall causes vast stretches formerly supporting tropical forest to dry out. Assassin grass savannahs come briefly to dominate again, pushing sunflower woodlands and remnant bamboo forest towards the south pole and the northernmost edge of what remains of Striata.

For now temperate and tropical forests persist in cooler polar regions and along the shores of the diminishing inland seas and wide rivers, but these inland bodies of water too will now begin to drain away across most of the continents as temperatures rise. As the continents continue to converge and crash together, as volcanism continues to pump the atmosphere with carbon dioxide gas and temperatures rise, a new trend of widespread desertification - on a scale Serina has never before seen - will become the norm over much of the world.

The Sea

Acid rain and rising global temperatures begin to destabilize Serina's oceanic ecosystems at the end of the Thermocene, simultaneously lowering the pH and availability of dissolved oxygen of seas worldwide, with drastic consequences to life. A mass die-off of hard-shelled organisms begins first, with clams, coral-hydra and other reef-builders in particular being unable to produce the shells they need to survive. Reefs are the first ecosystem to die out, the living builders bleached by warming seas and the non-living limestone foundations breaking down as a result of an influx of carbonic acid into the oceans from a carbon-saturated greenhouse atmosphere. Toxic algal blooms - "red tides" - will continue to become more numerous and longer-lasting as a result of the high levels of carbon dioxide present in the water providing favorable conditions for their development, and now sometimes cover massive portions of coastal seas, causing mass die-offs of marine life through the toxins produced when each individual algae cell in the bloom die off. As red tides become more abundant in shallow surface waters, they simultaneously block sunlight from reaching other plants and algae in the water and greatly deplete the oxygen in the water around where they bloom, further causing harm to fish and other aquatic life. In the wake of severe algal blooms, a positive feedback loop can result in the complete breakdown of the marine ecosystem as reduced oxygen results in die-offs of plant and animal life and subsequently lower the oxygen content of the water even more as these lifeforms then begin to decay. Worsening matters still, a sudden global die-off of marine life results in a huge surge of nitrogen into the global oceans, fertilizing still more and worse red tides. Seas across Serina become increasingly unstable at the end of the Thermocene, prone to large deoxygenated patches where few if any higher animals can survive.

The Life

The end of the Thermocene epoch will also be the end of many animal groups, particularly in the sea. Not only the shellfish will be negatively affected, but rather entire food chains. By 175 million years PE, plankton numbers and the ocean fish stocks which depend on them have already begun to plummet in the wake of widespread anoxia events. The large marine birds and predator fishes follow suit, barreling towards extinction, as the end of the Thermocene mirrors its beginning, only at an even more severe scale of ecological collapse.

On land, the decline of forests in place of grassland and desert is bad news for large browsers - serestriders and the large avitheres begin a rapid decline as the trees they feed on are pushed north and south by desertification. Though they will hold on for a while yet, as it will be several million years more before the continents fully collide, the inland seas drain completely away, and the forests they depend upon are completely displaced, for most large browsers their days are numbered in coming millennia. As for the trees themselves, temperate and taiga forests are pushed away even from the extreme poles by spreading tropical flora. From here on out, their hold-outs will be the peaks of polar mountain ranges, but as the climate becomes hotter even these refuges may prove unsuitable for their survival in the long run.

The collision of the eastern and western hemispheres with both one another and the Kyran islands results in a significant faunal interchange. Vivas move westward and serestriders into the east, the first time their groups will have met since diverging over one hundred and sixty million years ago. The Kyrans' aberrant island endemics - elefinches and their more primitive kin - face influxes of aggressive competitors, and by the end of the Thermocene the majority of their native wildlife will have died out through a harsh combination of drying conditions, as the equatorial island's lush forests are displaced by dry grasslands - particularly the aggressive and poisonous assassin grasses, to which none of their native flora or fauna had evolved any resistance to - and competition from animal invaders from the east and west.

The next few million years will bring the most extreme changes to the world of Serina its biosphere has yet experienced in its history. In the game of life, there will be many losers when this epoch concludes. But there will also be winners, as groups formerly kept to specialist niches find a place in the sun as for many of their competitors, the world they've known comes to an untimely end.

The world of Serina will soon be a very different place, though for now familiar life clings to their old ways in the increasingly small patches where the forests that formerly dominated the moon still thrive.