Issue 21: the evolutionary and restorative reasons we love the smell of oncoming rain
The science behind our ability to sense a storm before it starts.
We’ve probably all experienced it.
It was a phenomenon known long before it was understood.
The smell of rain in the air after an extended period of dryness is enticing and invigorating.
But it wasn’t until the 1960s that we knew what caused it. That’s when a pair of Australian scientists – Isabel ‘Joy’ Bear and Richard Thomas – described that the “pleasant and refreshing odour” comes from an oil released by parched earth before rain begins to fall.
The oil is created by the absorption of atmospheric contaminants, including decomposition products from animal and vegetable matter. Absorption is accelerated in hot, low-humidity conditions.
Bear and Thomas found that when humidity increases – a precursor to rain – it creates moisture, which fills the pores of rocks and soil, and flushes out the fragrant, yellow-coloured oil trapped inside.
They named the oil ‘petrichor’, a compound of the Greek ‘petra’, for stone, and ‘ichor’, which, in Greek mythology, is the ethereal fluid considered to be the blood of the gods.
Australia’s Commonwealth Scientific and Industrial Research Organisation (where Bear and Thomas worked), say scientists suggest that we inherited an affection for the smell of petrichor from ancestors who relied on rainy weather for their survival.
More recently, scientists have discovered that oil released by certain plants before rain, doesn’t just smell good, it makes us feel good, too.
A recent paper by Gary Paul Nabhan, Eric Daugherty, and Tammi Hartung describes their research in the Sonoran Desert of Arizona (home to the Saguaro National Park and Organ Pipe Cactus National Monument).
The area is “a mosaic” of trees, shrubs, cacti, succulents, vines, and grasses with oil-rich foliage, blossoms, and bark.
Like petrichor, many of these oils (“no less than 60”) are released by the increased humidity at the onset of a thunderstorm, creating an “orchestra of fragrances”.
Nabhan, Daugherty, and Hartung identified that 13 of the oils contained compounds capable of “enhance[ing] human physical and psychological health”, including improving sleep patterns, stabilising emotional hormones, enhancing digestion, heightening mental clarity, and reducing depression or anxiety.
While this sounds nice now – and indeed, ‘forest bathing’ walking tours are hosted in the area – the scientists caution that it could become crucial in the future.
More frequent heat waves and longer periods of drought will increase the quantity of oil the plants are able to exude, which may play an important role in stress resistance and adaptation to extremes.
“Inhabitants of arid lands may more urgently require the very health benefits that are generated from frequent engagement with or immersion in the Sonoran Desert’s aromatic plants.”
Thanks for reading. Feel free to hit reply to share your thoughts or feedback.
Til next time,
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