Catastrophic event

"Outside, the air is a red deadly gas that spreads from the plains of Africa, to the North Pole, making visibility limited to just a few feet away..."

Long has been the time since human beings wandered freely throughout the Earth. Enjoying the natural sun light, breathing natural fresh air and spending a day at the beach are memories written in old dusty books found in the darkest corners of the oldest book stores and abandoned book libraries.

For 500 years the healthy-looking blue planet that we used to see from space underwent a gradual and irreversible process of monumental deterioration. Due to the high pressure produced by civilization on the planet, and the increasing stress provoked on the Earth's fragile environment, the Earth's natural wild life suffered a huge modification:

"Extremely acid rains started to kill vegetation and starved thousands of animals. Species quickly became mutated to the point of impossible genetic recovery, and due to low healthy food supplies went extinct. The oceans turned to acid killing most aquatic life forms..."

This gradual change in the wildlife also impelled a gradual change in people's lives; they started being obligated to wear masks to cope with the outdoor air and began avoiding contact with rain. Houses began to be air sealed and refilled with clean oxygen provided by an in-house air renewer machine (aka ARM's). Entire streets started to be enclosed with huge metal structures and air sealed to provide better protection against the obstructive air. Not long after complete city blocks were being enclosed, entire cities, states, countries! It didn't take long for mankind to find itself living inside a mega intercontinental structure that extended to various regions of the planet!

Despite all acknowledgments and international efforts made century after century, the atmosphere became completely hostile; the very constituents of the atmosphere itself turned the planet into a self-contained sphere of highly deadly toxic gas. For 250 years, Humans were forced to live in this metallic structure served to protect humanity from the involving gas and provide the entire Earth's population with clean, breathable oxygen. No contact with the exterior was possible since the air became corrosive to most metals. The only metal resistant to the gas, Xzeno, was nearly all used up in the construction of the multi-mile-long mini-structures than made up the intercontinental structure.

Having this hostile environment did not, however, extinguish our abilities, and the attempt of colonizing other planets continued. The rest of the available metal was accounted for to build space shuttles. The Earth's moon quickly became a second home, providing Humans a much less hostile place to live in. Humankind continued it's dual-planetary life and continued their quest to colonize other planets, namely Mars, which they successfully achieved a century later.

"At that point we started to build another space station in Mars' orbit and using the Earth's moon as thrust towards Mars, trips to the red planet became more regular. A mysterious corporate entity (Central Trading) was established there in order to supply energy to future colonies."

All was seemly under control but as happened as before, what Humankind thought to be under control showed itself being uncontrollable. A few years ago, the gas involving the intercontinental structure on Earth also evolved and turned into corrosive sub-atomic particles. For years these particles aggregated themselves on the cooler areas of the outer walls of the engine rooms that provided continents clean oxygen, and long before they knew it entire countries became infected.

"The very little access we had to the toxic air gave us very little information on it."

People and animals died in millions. Entire countries were being shut off from uninfected areas, but as knowledge was very little on symptoms and propagation, little did humanity know that the particles had spread throughout the entire world.