If you've ever visited Old Faithful and the other geysers at Yellowstone National Park, you've likely come away with two reactions. First, it's one of the most captivating sights in all of nature. Second, the place stinks like rotting eggs.
That noxious smell is because of the small amounts of hydrogen sulfide gas given off by the geysers. Sulfur and its compounds are notorious for their stinky odor — the ancients even designated sulfur the "Smell of Hell", though that may have also had something to with sulfur's association with fiery volcanoes. Sulfur is also what makes skunk spray stink so horrendously. All mammals seem to have a natural distaste for the smell of sulfur, and now we know why. Weirdly enough, it's all about copper.
Scientists at Duke and the University of Albany examined why mammals, humans very much included, are so good at detecting even the tiniest trace amounts of sulfur, particularly when we're so repulsed by it. Duke researcher Hiroaki Matsunami explains:
"While we were doing our experiments, on even very dilute specimens of [the sulfur-based compound] MTMT, our neighbors on the lab hallway complained. We learned that copper was the metal that allowed for detection of all the sulfur-containing compounds we tested, and it was [fellow researcher] Eric Block's idea that metal ions must be involved. Further, I see no reason why the mouse receptor activity would be different from human receptors, because we have the same kind of olfactory receptors."
Basically, one our odor receptors is being supercharged by copper, so that it's really good at detecting sulfur. When the researchers decreased the amount of copper in the mice's noses, they suddenly struggled to pick up on the sulfur in MTMT. It's the first time that scientists have ever seen a metal play such a role in the functioning of the senses. The real question now is which genius is going to come up with some sort of anti-copper nose plug, so that we can all enjoy Yellowstone and skunks alike, without having to worry about the smell. Actually, I think I better get to work on that myself. I'll see you all when I'm a billionaire!