In 1998 the likes of Armageddon and Deep Impact offered film fans around the world an insight into the nature of a near earth object colliding with the blue planet. How realistic these portrayals of a meteor induced curtain call on life as we know it is a different matter, but it is fare to say the possibility of such an event came to the forefront of the public conscious afresh and in somewhat vivid detail.
We shall address the question of when, (and note ‘when’, and not ‘if’ dear reader), an asteroid of significant enough size collided and destroyed all human life and why it would achieve that, in a moment. But first, how can we be sure of that certainty? By way of analogy, a blindfolded ‘sniper’ with an infinite number of bullets who had no special training whatsoever, and an infinite time frame, would hit a shooting target at it’s perfect centre situation 3000 meters away, even after being spun 1000 times to confuse the shooter, would EVENTUALLY achieve the objective of hitting it’s perfect middle. You see in infinity the smallest possibilities eventually occur. In the infinity of time, you would eventually toss a coin heads side up a one hundred million times in a row.
An asteroid or comet could only hit in two possible places; on land, or in the sea. Both are catastrophic if the object is big enough. And there are plenty of those around folks, the vast majority not heading for us though.
If a big enough asteroid or comet hit land and resulted in the end of life as we know this would be followed by numerous catastrophic events. Firstly, and most obviously whatever life was hit directly by the object would be immediate flattened, need I say more? Second, most life within the blast radius would be certainly killed by the catastrophic shower of fire and brimstone. Either burnt alive or killed via the destruction of matter e.g. rocks, buildings, etc. If the blast radius was limited enough to not contribute to immediate global annihilation then the global dust blanket would effectively shut down our ecosystem by blocking the sunlight. We would then starve and/or freeze. If the object hit water; huge tsunamis. Or, and more likely, if the object was big enough, the impact would create enough heat to evaporate our oceans and then blacken our skies for 5 years ish blocking out sunlight and shutting down our ecosystem. It’s pretty horrific either way.