After two months of drought Waterfurlong has finally experienced a welcome deluge, bringing with it one of the most delicious of all garden scents - rain on parched earth.
You’ve probably come across the name for this -petrichor - derived from the ancient Greek petra (stone) and ichor (the golden fluid said to flow through the veins of the gods). How surprising to discover the word was only coined in 1964 and not by a poet but by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO).
When scientists Isabel (Joy) Bear and Richard Thomas of the Division of Mineral Chemistry in Melbourne decided to investigate the phenomenon, they found a small Indian perfumery had successfully captured and absorbed the elusive scent in sandalwood oil. The perfumery called it matta ka attar or ‘earth perfume’, but its origins remained as mysterious as ever.
Bear and Thomas embarked on a series of experiments and eventually discovered a yellowish oil trapped within soil and rocks that had been exposed to hot, dry, outdoor conditions. The oil was found to be secreted during periods of drought by soil-dwelling bacteria as an ingenious means of signalling to nearby plants that they should halt root growth and seed germination. This fragrant oil was released by contact with water. Bear and Thomas published their findings in the journal Nature, naming the oil petrichor – the blood of the stone.
When rain-clouds eventually build up after hot, dry periods, humidity in the atmosphere fills the pores of rocks, sand and soil with tiny amounts of moisture. This begins flushing the oil from the stone and releasing petrichor into the air. Once raindrops hit the arid ground the process intensifies and the scented elixir carries far and wide on the wind.
During the last few years The Massachusetts Institute of Technology (MIT) has taken the research a stage further. Using high-speed cameras, its scientists have observed that when a raindrop hits a porous surface it traps tiny air bubbles at the point of contact. As in a glass of champagne, the bubbles then shoot upward, ultimately bursting from the drop in a fizz of aerosols. Watch MIT’s slow-motion video of the petrichor process in action. (1)
Whilst recent downpours have begun to refresh our gardens
and defer the spectre of a hosepipe ban, how much more relief they must bring in hotter climes. The novelist Alexander McCall Smith often refers to the delight of smelling rain in the air in his marvellous Botswana-based No 1 Ladies Detective Agency series.
‘Mma Ramotswe awoke and lay in bed listening to that most blessed of sounds - rainwater drumming on the tin roof of a house. It was what the country desperately needed if the crops were to be saved and the cattle to flourish. It would heal the earth and soothe the minds of the people and the animals waiting for just this relief. It would lower the temperature and bring cool and green to a land that for months had been hot and brown. The blessing of rain was the one thing in Botswana that would unite those who might disagree about much else: pula, the word for rain in the Setswana language, also meant good fortune - ‘Pula! Pula! Pula!’was the encouraging chant that children learned in school and carried in their hearts for the rest of their lives.‘Pula! Pula! Pula!’‘(2)
SOURCES AND ACKNOWLEDGEMENTS:
(1) © Massachusetts Institute of Technology (MIT)
(2) The Woman Who Walked in Sunshine © Copyright Alexander McCall Smith: Little, Brown: 2015
Copyright © Karen Meadows 2018