Engage: The Smell of Soil

Phenomena: The smell of soil

The smell of soil, and the earthy taste we get from root vegetables like beets, is due to a compound called Geosmin, produced by soil microbes called Streptomyces. Humans are extremely sensitive to it and able to detect extremely small concentrations. Since it is strongest smelling in recently wetted soils, one hypothesis is that we evolved a sensitivity to Geosmin to help us find areas with water. Ask students to close their eyes and imagine the smell of rain.

Pass a moist soil sample, or root vegetable, such as a beet, around the class and ask students to smell it. Then discuss their associations with the smell of soil.

See the following articles for further details:

The Smell of Living Soil
The Smell of The Soil
What Makes Rain Smell So Good
Petrichor: why does rain smell so good?

Time required: 15 minutes to complete activity and discussion.

Alternate Phenomena:

Students will read the following Atlantic Magazine article describing the discovery of a soil virus that saved a life. 
A Dying Teenager's Recovery Started in the Dirt A Dying Teenager's Recovery Started in the Dirt  
Time required: 20 minutes to read the article and discuss it.