A FISHY AFFAIR

In an unprecedented turn of events, strange seismic activity ripples across the globe, awakening volcanoes that spew not lava and ash, but an invisible gas. Surprisingly, this gas poses no harm to mammals and insects, but it proves lethal to humans despite gas masks and medications. Faced with this existential threat, humanity is compelled to seek refuge in the one place where the gas cannot reach: underwater.

Global migration to the seas and oceans commences, with the construction of underwater cities using anti-corrosive metals and moisture-resistant materials. As the population swells, people are compelled to move farther away from the shore, braving the increasing water pressure. While some progress deeper into the ocean floor, others settle in coastal parts, ponds, and lakes, which provide easier movement and cleaner water.

To facilitate life underwater, famous automobile brands design stylish submarines and closed boats equipped with filtration systems. Scientists and engineers develop technology to extract oxygen from water efficiently, ensuring a constant supply of fresh air in every underwater house. Special boxes are designed to remove carbon dioxide from rooms, releasing it into the water. Clothing brands create fashionable diving suits with built-in heating systems to combat the cold temperatures.

Underwater mills generate electricity, and high-speed trains travel through vacuum pipes. Aquatic farms are established, where livestock graze on grass and seeds, while oxygen-producing plants thrive in incubators. The human body adapts to the underwater environment, with smoother skin and stronger muscles developed through constant movement against water resistance. Swimming becomes a daily exercise, resulting in a physique akin to Olympic swimming champions.

Doctors, biologists, and engineers collaborate to create masks that allow people to breathe underwater like fish, eliminating the need for oxygen tanks. However, the reduced sunlight exposure underwater leads to vitamin D deficiency, causing depression and weakened immune systems. To address this, scientists install huge ultraviolet lamps to illuminate the seabed and compensate for the lack of natural sunlight.

Life in the underwater cities mirrors life on land in many ways. People frequent cafes, cinemas, and gyms, pursue education, work, and abide by familiar laws. However, they navigate through water instead of walking the streets. The underwater world proves resourceful, with abundant reserves of oil, minerals, and valuable commodities, driving economic growth. Mega-cities emerge in the depths, while lakes transform into sought-after resorts.

On the surface, the abandoned traces of human civilization vanish, with nature reclaiming deserted cities. Animals, free from human interference, thrive, and seismic activity reshapes the land, submerging buildings underground. Fish, facing increasing pressure from humans, evolve to adapt to their new challenges. Some develop limbs and crawl on land to escape predators, gradually transitioning into mammalian-like creatures.

Meanwhile, humanity endeavors to build powerful spaceships to search for a new habitable planet. As space exploration advances, there is a growing realization that Earth's limited underwater space is insufficient, and the water is becoming polluted. Oxygen depletion threatens vital seaweed and photoplankton, the primary oxygen suppliers. Acknowledging these challenges, humans prepare for the gradual evacuation of Earth, spanning several centuries.

In the midst of this, octopuses, evolving at an accelerated rate due to the volcanic gas, surpass mammals in intelligence and mastery of the environment. Observing the mass exodus of humans into the sky, octopuses witness a familiar pattern from their ancestral memories deep within their DNA. They embark on their own journey, constructing their civilization, utilizing tools, and discovering remnants of the extinct human civilization.

As the octopuses unlock the secrets of the past, humans explore the vastness of space and encounter a highly intelligent humanoid species resembling octopuses. These beings share the history of their own civilization on Earth, where they, too, faced oxygen toxicity. In their case, the octopuses sought refuge in the ocean and subsequently adapted, while these humanoid octopuses ventured into space.

As the tales of both species intertwine, it becomes evident that the cycle of evolution and adaptation has repeated itself. The octopuses of Earth now realize their origins and collaborate with the space octopuses. Together, they ponder the mysteries of the vanished human civilization and embark on a new era, one where octopuses rise to prominence as the dominant species on Earth once more.