During the Great Famine, we learned that a Burger King ketchup packet has 10 calories. It's enough to keep an 180 pound man alive for about 60 seconds. Of course, by then, there weren't very many 180 pound men.Some people believed that the end of the Mayan calendar in 2012 presaged the apocalypse.
A Taco Bell hot sauce packet only has 2 calories.
We now can call those people out for what they were: Wildly, irredeemably, laughably optimistic.
As we huddle down below in our underground warrens, eking out our meager existence under the iron rule of unseen yet all-seeing authoritarian rulers, hiding from the radiation-soaked landscape that, paradoxically, is the only thing keeping us alive by holding the nanobiotic death clouds at bay, we can only wonder: How did all this happen?
When the al Qaeda suicide bomber detonated his radiological dirty bomb, we had no idea that the resulting chaos would guarantee that a 12.5-meter-wide meteor would slip silently past our laughably meager Spacewatch efforts and explode over Europe. The resulting electromagnetic pulse disrupted the safeguards of the Large Hadron Collider at a critical juncture, causing the creation of micro black hole, which lasted long enough before dissipating to pass through the earth's core, emerging in a remote island, notable only to those cleared to know about the secure bioweapons research and storage facility it housed.
The resulting explosion ejected an unholy and unknown melange of fearsome, genetically-engineered biological agents into the atmosphere. The ensuing plagues caused interlocking waves of pandemics, creating an omnidemic that devastated the global population.
Desperate to stave off extinction, researchers unleashed a nanobiotic countermeasure, whose networked, emergent intelligence first targeted the bioagent, then its vectors, then in cold machine logic, potential hosts.
In a perverse utilization of resources, the nanobiotic agent first converted human carriers into what can only be called zombies. Within days, though, the infection and exsanguination method of the now-cybernetic killers quickly evolved from clawing, tearing and biting, to a far more efficient method of host elimination, where moments after the first lungful of nanomachines would explode the victim into a wet, melted mess of red gore and grey goo.
In perhaps the only bit of luck humanity experienced (if one can call thermonuclear annihiliation "luck"), a few warring countries unleashed their arsenals in a vain, spiteful settling of final scores, leading to the discovery that the high levels of radiation were the only thing to give the nanobiotics pause.
The ensuing retreat to subterranean shelters under the cover of nuclear self-immolation was enough to keep humanity angstroms from the abyss. Though even if the nanobiotics can be beaten, the surface world remains a toxic, radioactive wasteland of under the cold, dim light of nuclear winter.