Biogeology

The Hollow Earth Tunnels have been a mystery for thousands of years, rarely any recordings of it exist, and most who have explored it have never seen the light of day again. For the Hollow Earth Tunnels are not empty - in fact, they are teeming with bizarre lifeforms far removed from the influence of the surface. But what could possibly have caused this underworld to be?  The answer is water.  Millions upon millions of years of limestone dissolution and erosion by acidic groundwater streams have slowly carved these vast underground tunnels before draining out. These tunnels provided an environment for pioneer species to colonize and shape into a stable community - eventually making way for additional visitors from the surface. 

But no other feature of this world has so significantly impacted the course of evolution than the high amount of radionuclides in the upper crust - caused by tectonic uplift, hydrothermal venting, and magma upwelling. The presence of this material initially left patches of Asia barren, until certain hardy plants and fungi developed the ability to store and metabolize the ionizing radiation for more energy than with sunlight. Some plants are so specialized for radiosynthesis, they can live completely independent of the sun, as can be observed deep within the Hollow Earth Tunnels in forests featuring a bioluminescent glow. On the surface, these irradiated biomes have created unique niches for unlikely creatures.

Another unique geological feature of Radiocene are extra islands in the Malay archipelago, west of Sumatra, being the North and South Mondo islands. The Mondo islands were historically hard to reach due to being surrounded by violent reefs - and were named after their immense size (Mondo → "world" in Italian). They were briefly colonized by the Dutch until the unforeseen arrival of skull crawlers forced them to flee. Even with such a short period of settlement, the Dutch East India Company had already significantly damaged the ecosystems, leading to the extinction of a native tiger species and endangerment of various fauna.