Ebola is not as infectious as the flu.
So, right now there's at least few thousand people carrying the virus. At least a few of them probably have other cold/flu viruses in their systems. If both Ebola and flu infect the same cell, they can exchange genetic information, potentially resulting in a much more easily transmitted strain of Ebola. The more people that are infected, the greater the chance such genetic exchange could occur. It wouldn't take much for Ebola to become a first world threat.
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."