At the study's start, the group of parents who were most opposed to vaccination said that on average, the chance they would vaccinate a future child against MMR was 70 percent. After these parents had been given information that the MMR vaccine does not cause autism, they said, on average, the chance they would vaccinate a future child was only 45 percent — even though they also said they were now less likely to believe the vaccine could cause autism. Vaccination rates are currently high, so it's important that any strategies should focus on retaining these numbers and not raise more concerns, tipping parents who are willing to vaccinate away from doing so. 'We shouldn't put too much weight on the idea that there's some magic message out there that will change people's minds.'"
Your post deserves a much better answer than what you have received thus far. Unfortunately I am not a physicist and my communication skills are terrible, but I will give it a try. Hopefully someone else will come along and give a much better explanation.
As I understand it, destructive power comes from energy impacted by the projectile. One way to achieve that energy is to have the projectile explode (bombs, artillery shells, nuclear explosions) or just using the kinetic energy (bullets). It is the later type that is being pointed to.
The damage of the kinetic projectile is (I think) based on the mass of the projectile and the amount of force used to propel it forth. Essentially the more dense the projectile and the more force is used to launch it, the more energy it will transfer on impact. Given large enough values, it is possible that a pure kinetic projectile can transfer more energy than a nuclear explosion.
The premise of the post is the assumption that a projectile (rocks and rods) simply thrown from a satelite towards the surface of the Earth, has enough potential energy to achieve this level of destruction.
Or to put it another way. Imagine you are on a train. The faster the train goes, the more energy it'll have if it were to impact. A train going 5 miles a hour might put a dent in a car, but it wouldn't be a disaster. A bullet train moving at 300 miles a hour suddenly hitting a inexplicably appearing car will be on international news. Now, Imagine a titanium rod 10 feet thick being accelerated to escape velocity from the moon. It'll experience minimal slowdown to the almost non-existent lunar atmosphere. As it begins to re-enter the earths atmosphere, it continues to absorb energy. The faster it moves, the bigger the amount of potential energy it'll have. By the time it arrives at it's target, the forward momentum will be translated into a large amount of energy. I am in no way qualified to state how much energy, but I'd imagine that anyone in a 3 block radius MINIMUM will have to adjust to the idea their flowers are now a pile of ashes. As well as the people themselves. And the buildings. I'm going to say you'll need to fill in a rather large crater now.
Seems like a no-brainer to me. Why go out and dig up fossils when you can just print up a dino-bone. Gap in the fossil record? No problem. Just print up the missing link using a 3d morphing tool and be famous.
Except, you know, carbon dating, Mineral analysis, etc.