Part of the show Naked Scientists Question and Answer Show
When a meteor hits the Earth like the one that was supposed to have killed off the dinosaurs, it hit with the impact of hundreds or even thousands of nuclear bombs going off. Why was that? If I was to throw a large rock off the Empire State building it would make a big crater but no fire, no explosion, no nuclear reaction. Why is this?
When you actually have a meteor or an asteroid hitting the Earth it doesn't create a nuclear reaction its literally just the energy from the speed that it hits. If you drop a stone off the Empire State building it will probably hit the floor at a few metres per second, when an asteroid comes in and hits the Earth its probably coming in at maybe 20km per second. Incredibly fast – what we call hyper-velocity, and literally that energy from such a massive object, it could be hundreds of metres or even kilometres across, hitting something and basically stopping dead – all that energy from the speed it was going at gets immediately converted into heat or sound waves propagating through the crust of the Earth. It can do immense damage to the Earth and basically blast vast amounts of rock and debris up into the atmosphere which can cause climate change and all sorts of nasty problems.