The sky is falling!
You might already know this, but a large meteor struck in Norway on Wednesday.

As I said, you may already know this. But did you know it hit with a force of at least a megaton? The fact it hit in the middle of nowhere means we lucked out. What if it had grounded in a major city? Think what it could have done to London. New York. Moscow. Tokyo. New Delhi.

There would have been no warning. No time to evacuate. Instead an area slightly smaller than a football field would have been leveled in an instant. Everything within two kilometers of the blast zone would have been subjected to extreme heat and pressure. Close to the blast zone many buildings would have collapsed, while further away they might just have lost every window. Many would be on fire within the inner zone.

Inside that two kilometer radius there would be a lot of survivors, but the numbers of the dead would be horrifying. Rescuing the survivors and getting them to hospitals would be enormously difficult; streets filled with rubble and the air filled with dust and smoke. Immediately outside the circle the buildings might be relatively untouched, but the streets would be jammed with people and emergency vehicles.

The situation would be nearly unmanageable from a governance and policing viewpoint. The zone of destruction would be too large to rope off or keep people out of; and that would probably be a good thing as many of the injured would initially be carried to safety by volunteers. There will almost certainly be a small amount of looting. Journalists and video crews will be wandering around making lame comparisons to 9/11. The smarter ones making somewhat less lame comparisons to Hiroshima. Within a few hours construction equipment will be pressed into service to pull down dangerous buildings and clear streets.

They will probably still be finding survivors days later. Getting out all of the dead will take longer yet. The final death toll would vary by location, but could be as high as fifty thousand. All from a rock falling out of the sky...

And this is only if it fell onto land. What if it fell into the harbor of a great city? The resulting tidal wave would make the devastation of New Orleans look puny.

Can you imagine it? Now imagine a bigger one; one large enough to destroy the entire city. Larger yet? A small asteroid capable of laying waste to hundreds of square miles and putting enough dust into the atmosphere to affect the weather for decades.

Still able to imagine it? OK, let's scale up an order or two of magnitude. An extinction event. One big enough to crack the planet and blacken the sky for a hundred years.

I don't know if you can really have something like that in your head. Personally I lost my ability to really envision the results somewhere around the small asteroid. But all of these things are possible. Hell, objects of each of the sizes I described have already pounded this planet over and over and will certainly strike again. Whether one will ever strike an inhabited area is unlikely, but something we should keep in mind.

So, we are willing to spend how many billions of dollars and expend how many lives to fight terrorists capable of killing a few hundred to, at most, a few thousand? How much more should we commit to avoiding a possible extinction event?

Well? How much?