Or there could be a nearby gamma ray burst.
There isn't much point in worrying about this. About the only people that would be spared on the side of the earth that was exposed would be people that were already underground/under water at the time. How far underground/under water would depend on the intensity of the gamma rays. Even if we detected a burst of neutrinos to alert us that something was coming, it wouldn't be enough warning for anyone to take shelter that wasn't already there. I guess if you really wanted to be safe you could live a few hundred feet down in an old mine, but that would rather suck.
Less significant (but not evidenced in the DNA or fossil evidence) would be multiple independent species making the transition from sea to land
We don't need fossil evidence. There are species of crabs that live on land. Mud-skippers live mainly in the water, but could easily evolve to land based animals.
The only event of that magnitude that we have evidence of created the moon.
So what is to say that there wasn't a technical civilization on earth before the creation of the moon?
No, the 3000km is assuming that you are using the aluminum air battery in addition to the normal lithium battery."
In order for friction to destroy steel, it needs to actually wear it away one particle at a time. Being so much heavier/denser, there are that many more particles to wear away.
Or, you know, heat it up so much that it starts to melt. That's a real possibility for this application. A previous poster suggested rheostatic brakes (basically regenerative braking, where the electricity is dumped into a big resistor instead of being stored for later use). It would add weight and complexity, but if regular brake disks can't dissipate the energy fast enough, then something like that might be necessary.
Variables don't; constants aren't.