petrichor
ˈpeˌtrīkôr/
ˈpeˌtrīkôr/
This week on the Bluefish Editorial desk, it RAINED.* Some of you in other parts of the world may not fully appreciate how thrilling this is. As a rule, we in San Diego only ever get rain between November and March, and the last few years not even then. The state’s record-breaking drought was eased by last year’s wet winter in Northern California, but even though SoCal has shared in this bounty (thank you California Aqueduct!) we have seen precious little actual rainfall.
But this week we got a good drenching. My neighbor’s backyard gauge read a whopping 2.5 inches. The garden is looking fresh-washed, and the leaves have got that sheeny plumpness they never get under the sprinkler.
And I have had occasion to contemplate a lovely word that gets very little use around here: “petrichor.”
But this week we got a good drenching. My neighbor’s backyard gauge read a whopping 2.5 inches. The garden is looking fresh-washed, and the leaves have got that sheeny plumpness they never get under the sprinkler.
And I have had occasion to contemplate a lovely word that gets very little use around here: “petrichor.”
You have probably noticed petrichor, even if you did not know what it was called. It’s that distinctively sharp, earthy scent that accompanies rain, especially after a long dry spell. Poets have talked about that smell for millennia.** And in fact we (like other animals) can detect this odor on the wind from miles away, possibly because our ancestors depended on being able to find water in often hostile conditions.
National Park Service: Rain on Ryan Mountain, Joshua Tree National Monument
But while we can smell it, and many love it, for a long time English didn’t have a word for it.
Until 1964, that is, when two intrepid Australian geologists, Isabel Joy Bear and Richard Grenfell Thomas, took it upon themselves to understand exactly what that smell is and where it comes from. Their article, “Nature of Argillaceous Odour,” appeared in the journal Nature, and their analysis proved unexpectedly illuminating for me.
I had always assumed the rain-smell is biological in origin: some bacterial funk in the ground loosening up and breathing out in the welcome presence of moisture.
But while this is to some degree true in wet, fertile regions, in deserts like the one I live in, the smell comes from the rocks themselves. Bear and Thomas demonstrated that pure mineral samples, even those heated in a kiln to destroy any organisms present, nonetheless release the odor when moistened or even breathed on. When they isolated and examined the substance, they found that it is the result of a reaction between the rock and plant oils in the air; this stuff accumulates in the rocks and soil in dry weather and then is released into the air when the humidity rises before a rain.
Until 1964, that is, when two intrepid Australian geologists, Isabel Joy Bear and Richard Grenfell Thomas, took it upon themselves to understand exactly what that smell is and where it comes from. Their article, “Nature of Argillaceous Odour,” appeared in the journal Nature, and their analysis proved unexpectedly illuminating for me.
I had always assumed the rain-smell is biological in origin: some bacterial funk in the ground loosening up and breathing out in the welcome presence of moisture.
But while this is to some degree true in wet, fertile regions, in deserts like the one I live in, the smell comes from the rocks themselves. Bear and Thomas demonstrated that pure mineral samples, even those heated in a kiln to destroy any organisms present, nonetheless release the odor when moistened or even breathed on. When they isolated and examined the substance, they found that it is the result of a reaction between the rock and plant oils in the air; this stuff accumulates in the rocks and soil in dry weather and then is released into the air when the humidity rises before a rain.
| Bear and Thomas proposed that this fragrant yellowish substance be called petrichor: a compound of two Greek words: petros (πέτρος) meaning stone, and ichor (ἰχώρ), the golden fluid that flows in the veins of the gods. Petrichor, they said, was the “tenuous essence” of rock—its uncanny aromatic lifeblood. |  National Park Service/Kathy Bell: Clouds on the summit of Ryan Mountain, Joshua Tree National Monument |
They didn’t know how right they were: this “tenuous essence” turns out to have powerful effects. It turns out that petrichor inhibits the germination of seeds, possibly as a way of keeping young plants from germinating too quickly at the first hint of rain (after all, there may not be more for some time). With steady, regular rain, though, the petrichor washes away and the seeds can sprout. But even then the ichor is not done—as it washes out of the soil, it flows on into waterways, where it serves as a signal to fish and frogs that the dry season is over and it’s time to start making babies.
So petrichor is a kind of lifeblood, circulating throughout the system, telling us that the water has come again, letting us know when it’s time to sprout.
So petrichor is a kind of lifeblood, circulating throughout the system, telling us that the water has come again, letting us know when it’s time to sprout.
I know that the rain was not so kind to other parts of the state. But here, the yard drank deep, the roof did not leak, and we breathed deep and counted our blessings.
| I feel like the earth, astonished at fragrance borne in the air, made pregnant with mystery from a drop of rain... —Rumi |
*No, not literally ON the desk, thank goodness, or I would be too busy blaspheming the gods to write this.
**Interestingly, while I found a fair number of Greek, Middle Eastern, and Australian poets talking about the smell of rain, examples from England itself are relatively rare. Paradoxically, the fact that the English live in a place where it rains all the time means they probably have little experience with true petrichor, which requires a long dry period to emerge. However, the English will not shut UP about the smell of dew, which operates on a similar principle.
RSS Feed