While you can blame meteorites on the aliens, there are far more dangerous things to hit the Earth, and they come from man himself. We're talking bombs here, and over the history of aerial warfare, there's been millions and millions dropped all across the world. How many? It's hard to say, but as an eye-opening example, over 450,000 cluster bombs alone were dropped on Vietnam, Laos, and Cambodia in a ten-year period. Just three countries, just in ten years, and just by the US.
With not all of them detonating on impact, and many just lying dormant in weapons caches, that leaves hundreds of thousands of potentially fatal bombs - UXO, or UneXploded Ordnance as it's known - almost everywhere on the planet. This particular bomb in the photo above was lying near a high school running track in Orlando, Florida. Just imagine how the villagers in South East Asia feel when they're going for a walk.