Bill Bryson's A Short History of Nearly Everything is a wonderfully entertaining and amazingly enlightening book. His insatiable curiosity to actually find out all the things he did and great dexterity as a writer to explain all that in wonderful prose are something to marvel at (For a detailed and wonderfully written review go here). As the title of the book indicates, included in the book is the history of earth and humanity and what is more, a possible end as well! Following passage from the book describes rather vividly how the end of humanity- The Armageddon- in the form of a cosmic collision between earth and a wandering asteroid will look like.
An asteroid or comet traveling at cosmic velocities would enter the earth's atmosphere at such a speed that the air beneath it couldn't get out of the way and would be compressed, as in a bicycle pump. As anyone who has used such a pump knows, compressed air grows swiftly hot, and temperature below it would rise to some 60,000 Kelvins or ten times the surface temperature of the Sun. In this instant of its arrival in our atmosphere , everything in the meteor's path-people, houses, factories, cars-would crinkle and vanish like cellophane in a flame.
One second after entering the atmosphere, the meteorite would slam into the earth's surface, where the people of Manson(an impact site of such a collision millions of years ago) had a moment before been going about their business. The meteorite itself would vaporize instantly, but the blast would blow out a thousand cubic kilometers of rock, earth, and superheated gases. Every living thing within 150 miles that hadn't been killed by the heat of entry would now be killed by the blast. Radiating outward at almost the speed of light would be the initial shock wave, sweeping everything before it.
For those outside the zone of immediate devastation, the first inkling of catastrophe would be a flash of blinding light-the brightest ever seen by human eyes- followed an instant to a minute or two later by an apocalyptic sight of unimaginable grandeur: a rolling wall of darkness reaching high into the heavens, filling an entire field of view and traveling at thousands of miles an hour. Its approach would be eerily silent since it would be moving far beyond the speed of sound. Anyone In a tall building in Omaha or Des Moines, say, who chanced to look into the right direction would see a bewildering veil of turmoil followed by instantaneous oblivion.
Within minutes, over an area stretching from Denver to Detroit and encompassing what had been Chicago, St. Louis, Kansas City, the Twin Cities-the whole of the Midwest, in short- nearly every standing thing would be flattened or on fire, and nearly every living thing would be dead. People up to a thousand miles away would be knocked off their feet and sliced or clobbered by a blizzard of flying projectiles. Beyond a thousand miles the devastation from the blast would gradually diminish.
But that's just the initial shockwave. No one can do more than guess what the associated damage would be, other than that it would be brisk and global. The impact would almost certainly set off a chain of devastating earthquakes. Volcanoes across the world would begin to rumble and spew. Tsunamis would rise up and head devastatingly for distant shores. Within an hour, a cloud of blackness would cover the planet , and burning rock and other debris would be pelting down everywhere, setting much of the planet ablaze. It has been estimated that 1.5 billion people would be dead by the end of first day. The massive disturbances to the ionosphere would knock out communications systems everywhere, so survivors would have no idea what was happening elsewhere or where to turn. It would hardly matter. As one commentator has put it, fleeing would mean, `` selecting a slow death over a quicker one. The death toll would be very little affected by any plausible relocation effort, since earth’s ability to support life would be universally diminished.”
The amount of soot and floating ash from the impact and following fires would blot out the sun, certainly for months, possibly for years, disrupting growing cycles. In 2001, researchers at the California Institute of Technology analyzed helium isotopes from sediments left from the later KT impact and concluded that it affected earth’s climate for about 10,000 years. This was actually used as evidence to support the notion that the extinction of dinosaurs was swift and emphatic- and so it was in geological terms. We can only guess how well, or whether, humanity would cope with such an event.
And in all likelihood, this would come without warning, out of a clear sky.