In PT1a Weekly Project Gutenberg Newsletter, Michael Hart wrote:
Even a tiny gold, platinum, or iridium asteroid under 100 feet in diameter could destroy the world's economic system, ...
Think such asteroids don't exist?
Just ask any dinosaur expert what wiped out those dinosaurs.
It was an iridium asteroid, and a lot bigger than 100 feet.
No, it wasn't "an iridium asteroid". It was an asteroid with about the average concentration of iridium for bodies in the solar system, which is to say, in parts per billion. The notable thing is that on Earth, most of the iridium is concentrated in the core; in the crust, iridium is (even) rarer than the solar system average. Thus, when a 10km asteroid of average iridium concentration slams into the Yucatan peninsula, you get a thin layer of rock (all over the world) that is "rich" in iridium, relative to the surrounding rock. But it's still just parts per billion. -Michael