- Education and Science
Petrichor: The Smell of Dust After Rain
Petrichor: the smell after rain
A summer storm breaks fast
The air is thick with sweet relief
Dry earth meets sky at last
“Petrichor” has two roots from the Greek language. Petra means “rock” in both Greek and Latin, and is also evident in the word “petrify” (meaning “to make stone”). Ichor is the mythological golden blood of Greek gods. In legend, it was lethal to mortal humans, which perhaps helps explain the obsolete medical use of “ichor” to describe infected fluid seeping from ulcers or other wounds. “Ichor” was also widely used since the 1600’s to refer to animal blood and by early twentieth-century geologists to label a liquid that oozes from magma.
The word petrichor can be traced to its first use in a 1964 Nature research publication by mineralogists I.J. Bear and R.G. Thomas of Australia's Commonwealth Scientific and Industrial Research Organization. They coined the term to describe the “essence of rock”—officially also known as “argillaceous odor.” Bear and Thomas also published additional related articles through Nature.
Plants, rocks, clay-based earth, and rain after warm, dry weather: these set the stage for petrichor. What we smell is a mixture of substances brewed by the rain:
-Plant oils: certain plants produce oils and lipids during drought-like conditions to self-protectively coat themselves from sun damage and their seeds against germination; these wash off with rain and are absorbed into clay-based soil and rocks
-Actinobacteria spores: the bacteria responsible for decomposing organic matter give off actinomycetes, which are what we first smell as rain starts falling
-Geosmin: the chemical odor source of a bacterial by-product in wet soil is released by agitation, such as from being stepped on or rained on
-Ozone: the presence of any lightning in a storm yields the faint smell of ozone in the air
Petrichor in "The Doctor's Wife"
Dr. Who and Perfume
Petrichor has appeared in the Dr. Who television show from BBC. Written by Neil Gaiman, “The Doctor’s Wife” episode used the sensory memory of petrichor as part of a telepathic password sequence. “Petrichor” was then revisited as a perfume advertisement in a later Dr. Who episode written by Gareth Roberts, entitled “Closing Time.”
The smell after a rainstorm is lush and distinctive, and widely experienced as pleasant or even enchanting. As illustrated in the science-fiction world of Dr. Who, perfumerers have taken note of petrichor’s appeal. For a perfumery perspective and recommendations of earth-based perfume scents: