OK, so the homework problem for the last couple of weeks in my geology class (that's a sophomore-level course I'm taking FOR THE FUN OF IT!) has involved calculating the diameter of the asteroid that probably hit the earth at the boundary of the Cretaceous/Tertiary periods (called the K-T boundary) based on the amount of iridium in the K-T boundary layer, the density of the iridium, etc. Lots of dimensional analysis, really. I've been fretting over it, but finally sat down today with a "more knowledgeable other" who helped me figure out how to get there from here.
It is a lovely feeling to be learning something new.