The smell of the earth!

Ever wondered what the smell of the earth is?  Maybe you've visited the countryside while farmers have been ploughing their fields and smelled it.  The smell is caused by Geosmin which is an organic compound with a distinct earthy aroma produced by a type of Actinobacteria.

Geosmin is produced by the bacteria Streptomyces, a genus of Actinobacteria and released when these microorganisms die.

Geosmin is a colourless liquid, with a boiling point of 270°C.  The human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion.  It is the smell after a rainstorm when the ground is wet.

Geosmin is often responsible for unpleasant tastes in water supplies. Cyanobacteria (blue-green algae) and actinobacteria release geosmin when they die, and this can be absorbed by bottom-feeding freshwater fish such as carp and catfish. Geosmin combines with 2-methylisoborneol, which concentrates in the fatty skin and dark muscle tissues. Geosmin breaks down in acid conditions; hence, vinegar, lemon and other acidic ingredients are used in fish recipes to help reduce the muddy flavour.

Geosmin can sometimes be tasted in wine or drinking water.

It has also been suggested that camels can detect the smell of geosmin that had been released by Streptomyces miles away in wet ground, and track the geosmin to find an oasis; in return the camel could carry away and disperse the spores of the Streptomyces bacterium.

Soil is considered to be the "skin of the earth" and consists of a solid phase (minerals and organic matter) as well as a porous phase that holds gases and water.  It carries essential nutrients for plantlife and is a habitat for organisms that take part in decomposition of organic matter and the creation of a habitat for new organisms.

For more information visit:-
http://web.expasy.org/spotlight/back_issues/035/
http://en.wikipedia.org/wiki/Soil