65 million years ago an enormous lump of rock – a comet or asteroid over a mile in diameter – crashed into the Earth at enormous speed – perhaps 200 times the speed of sound – leaving a crater 193 km wide and 48 km deep.
Think about that for a moment.
Much of the rock was vapourized on impact, leaving a thin deposit that can be found in layers of rock all around the world today. The explosion wiped out all the dinosaurs and led to the extinction of half of the world’s other animal species.
I don’t wish to alarm you, but this wasn’t the first time such a collision had taken place, and it won’t be the last.
In 1994 the comet Shoemaker-Levy 9 struck the planet Jupiter with the force of 6 million megatonnes – 75 times the explosive power of all the nuclear weapons ever built. It left a hole in Jupiter roughly the size of the Earth.
There are probably more than a billion asteroids wandering haphazardly around the solar system and two or three of them narrowly miss the Earth each week. One or two small ones actually hit the Earth’s surface every year. Tracking such objects is tricky as they are very small by astronomical standards and irregular in their motion. If one happened to cross the Earth’s orbit we probably wouldn’t even see it coming, and the Earth would smash into it at nearly 100,000 mph.
Even if we had telescopes trained to spot killer asteroids, we probably couldn’t do anything to prevent a collision.
Space is a dangerous place. Our continued existence is perhaps more precarious than many people realize. Don’t imagine that God or nature will look after us, because history demonstrates that’s not true.
For humans to continue to exist in the long term, we need to live on more than a single planet. If you ever need a reason for justifying the cost of manned space exploration, perhaps this is it.