Mankind’s fascination with the smell of the earth goes back millennia. It was not until the 19th century that the first chemists became interested in this aroma. In 1891, Berthelot and André extracted a compound with the characteristic odor from the soil. But why do we like petricor?
The odor arises when many clays and natural dry soils are moistened with water. It is due to a yellowish oil trapped in the rocks but released by moisture. Petricor is derived from the Greek petros (stone) and ichor. In Greek mythology it was the mineral present in the blood of the gods.
Camels and others
The aroma manifests itself when the oil is released and mixed with a molecule called geosmin. Many animals detect the molecules responsible for the earthy scent at extremely low concentrations. The fruit fly has an entire olfactory circuit dedicated to detecting this molecule, for example.
It is believed to help Bactrian camels in the Gobi Desert locate oases in the middle of the desert. They are able to sense the presence of geosmin tens of kilometers away. Far away in Australia, kangaroos show similar abilities.
The human sense of smell is extremely sensitive to the presence of geosmin as well. But why exactly do we like preticor?
Advantage and evolution.
A good sense of smell will be an evolutionary advantage for any organism. Some 200,000 years ago, our ancestors used their sense of smell to hunt. They used it to differentiate nutritious foods from harmful ones. And, perhaps, to quench their thirst.
The human affinity for geosmin may be rooted from those times. Our nomadic ancestors wandered across arid landscapes in search of water. Of course, this would be a compelling reason to answer why we are so attracted to the smell of wet earth. If we think about it carefully, it is a beautiful, subtle and bucolic strategy used by some bacteria to disperse. And thus increase their chances of survival and colonization of new territories.