That sublime earthy scent when rain falls on parched earth - particularly after a long drought in arid areas such as the Namib desert.
The word Petrichor derives from the Greek petra meaning “stone” and ïchör, the ethereal blood that flows in the veins of the gods of Greek mythology. Thus comes the expression ‘the blood of the stone’.
(Image right: A rare sight, copious rain in the Namib desert - riders enjoying the first rain in this area in eight years)
The heady aroma is said to derive from oils exuded by plants during dry period to retard seed germination. In the presence of moisture, the oil is released along with geosim, a metabolic byproduct of bacteria emitted by wet soil producing that distinctive scent. The scent is released as aerosols - small bubbles which float to the surface of rain drops - carrying both bacteria and viruses from the soil.
The lighter the rainfall the stronger the aroma, but it doesn’t even have to rain - just moisture in the air causes the pores of rocks and soil to open and flush the oil. When it does rain the scent is spread in the wind to the delight of all within reach.
(Image below: Our picketed horses watching the approach of rain at sunset)
In the presence of lightning, another distinctive scent is added to the mix - ozone. It is understood that lightning splits oxygen and nitrogen molecules in the atmosphere and they in turn can recombine into nitric oxide which reacts with other chemicals in the atmosphere to form ozone - a sharp smell faintly reminiscent of chlorine.
Whatever the science behind the wonderful smell, it matters not to those who have had the privilege of being there to enjoy it….