Ancestral Tale

A couple of odd phrases decorate the Chapter on the Cretaceous Catastrophe in Richard Dawkin's book The Ancestor's Tale. The first is "bullet wounds are hot because of the bullets velocity."

Now I had never thought about bullet wounds being hot, possibly since I haven't been shot much, but a fast rifle bullet has enough specific energy to generate some heat. The fastest bullets, travelling at about 1200 m/s, or 1.2 km/s, would probably heat themselves to several hundred degrees upon hitting something hard, like armor plate.

The second odd phrase is that cosmic projectiles, like the comet or asteroid that ended the Cretaceous, travel "even faster" than a high speed rifle bullet. Well yes, like tens of times as fast. Collision velocities up to 100 km/s or more are plausible, and velocities smaller than 10 km/s are implausible. So a large cosmic projectile produces specific energies (and temperatures) at least hundreds and most likely thousands of times greater than a rifle bullet (energy scales like the square of velocity). Add in the fact that it has a mass of trillions or quadrillions of tonnes and you can get real damage.

Just sayin.

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