Rain soaked ground and trees are always leaving a distinctive smells refreshing.There are many theories explaining the origin of these smells, one of the compounds released by the soil and rocks which petrichor.

This compound was first revealed by the 2 researchers from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), IJ Bear and RG Thomas.The study was published in a report entitled “Genesis of Petrichor” and published by the journal Nature in 1965.

Tuesday (12/07/2010), petrichor derived from 2 Greek words, namely Petros which means stone and ichor which means water. In Greek mythology, petrichor a smooth fluid flowing in the veins of the gods.

The researchers believe, a compound that has the chemical name 2-decanone was released by the plants in the dry season and then be absorbed by soil and rocks. By rocks, the compound was released back when the humidity is experiencing such a drastic change before and after the rain falls.

Until now, the theory developed by CSIRO scientists is considered most able to explain a phenomenon peculiar smell that smell before and after the rain.

There is also another theory that says, distinctive odor when it rains caused by the spores produced by bacteria called Actinomycetes. These bacteria usually live in moist soil, but easy to die when the soil is dry or lose moisture.

Before you die, the bacteria leave the eggs in the form of spores which have a much stronger resistance. In dry soil conditions, the spores were experiencing hibernation so it can live up to for years.

When it rains moisten the soil, spores were revived and some of them break away from the ground and inhaled by humans. The smell of rain was actually a typical spores are inhaled by humans.

This theory is corroborated by experimental results, which verify that culturing Actinomycetes spores in the laboratory can produce smells like rain. But this theory does not explain the similar smell that sometimes has appeared just before the rain fell.