It appears humans are more sensitive to fresh rain on dry soil than sharks are to blood in the water. Fun to think of the evolutionary pressures there.
From the wiki, humans detect at 0.4 ppb and it appears sharks are at about 1 ppm. I can't find a proper source, but several articles say about a teaspoon of blood to an olympic swimming pool. https://www.sharktrust.org/shark-senses
> Fun to think of the evolutionary pressures there.
Savannah hominids obviously needed to run to the parking and put up the tops on their convertibles as soon as they scented rain?
By etymology, I'd consider magma to be a good referent for petrichor. Or at least the salty deposits left along contact surfaces of strike-slip faults?
I imagine the evolutionary benefit of the sensitivity is in avoiding drinking stagnant water, where the compound is also present: https://en.wikipedia.org/wiki/Geosmin
Hominids traveling deserts may need to quickly climb when rain starts falling. If you're not prepared, you can get swept away and even drown by flash floods in the dryest places on earth.
The "more people drown in deserts than die of thirst" factoid is not entirely made up; flash floods are incredibly deadly, especially so in areas where it doesn't rain much. Modern humans are quite good at surviving such events but I can definitely see (early) mammals struggle to survive them.
Are individual scent receptors evolutionary preserved, or is there enough "cross-encoding" either at the genetic level or the receptor level itself that preservation of a small number of survival-correlated scent receptors will, coincidentally, cause preservation of other receptors as well?
While petrichor is pleasant after a rain, according to the wiki article on geosmin it appears to also indicate poor water quality [0].
So perhaps the evolved sensitivity is to avoid stagnant water, rather than to seek recent rainfall. After all, for prehistoric hominids local recent rainfall is pretty obvious, and traveling large distances to distant rainfall is not usually practical.
I always hated this word — it was made up in the 1960s, and it sounds to me like it is describing something disgusting that you’d scrape off the ground.
The pleasant smell of rain deserves a better word than ”petrichor”.
Hah! I like your interpretation as well. “I’m sorry sir, it appears you are suffering from a case of petrichor. A bracing draught of brandy ought to put this right!”
OMG, I'm Greek the word sounded awfully lot ancient Greek to me and I heard it a couple of times, even misattributed to Ancient Greek scholars etc.
It is a portmanteau of "πέτρα (petra)" meaning "rock" and "ιχώρ (ichor)" which is the mythological golden substance in the blood of the Ancient Greek Gods. So this sounds all pretty Greek to me with all the quirky mythological stuff that come with the Ancient Greek but here the thing.
Looking forward to tease my acquaintances that claim "our ancestors had such a diverse dictionary they even had a word for the pleasant smell of rain".
Living in the semi-arid American Southwest (about 15" of rain a year), the occasional brief-but-heavy rainfalls during late summer can give an overwhelming scent of petrichor. If walking or hiking outside, it's inescapable, since it literally comes from every patch of ground; and while pleasant enough in small doses, it can get strong enough that it feels hard to breathe, like walking through a desperate Macy's.
I went on a road trip once with a person who was born and raised in a large city, and we drove out into the country just after a rainstorm. It was summer and we could smell the rain on green leaves and soil smell. She said, "what is that wonderful smell in the air? I've never smelled anything like this." It was a really cool experience to be there and sort of experience it for the first time vicariously.
Recent discussion with friends on petrichor, many didn't like it, but most are also city dwellers that mistakenly associates it with wet concrete/building materials. Opinions flipped when explained it was wet nature/soil.
Funny timing that this particular topic made it to HN. From the recently-released Season 4 of The Dragon Prince, this is one of the reasons Claudia is so infatuated with Terry, an Earthblood elf.
”“A little-known piece of trivia,” Altman announced. “This smell, after it rains for the first time. You know what’s that called?”
“Is this going to freak me out?” Williams said.
“Petrichor,” Altman said. “It’s my favorite smell. You only get to smell this once or twice a year, because it has to not rain for a while, and then rain. It’s the smell of summers in St. Louis.”
From the wiki, humans detect at 0.4 ppb and it appears sharks are at about 1 ppm. I can't find a proper source, but several articles say about a teaspoon of blood to an olympic swimming pool. https://www.sharktrust.org/shark-senses