Petrichor is the distinct, earthy scent that occurs when rain falls on dry soil, which is actually caused by an oil produced by certain plants during dry periods and a chemical called geosmin.

A closer look

Petrichor is the distinct, earthy scent that occurs when rain falls on dry soil, which is actually caused by an oil produced by certain plants during dry periods and a chemical called geosmin. Geosmin is secreted by soil-dwelling bacteria known as actinomycetes, and human noses are incredibly sensitive to it, capable of detecting it at just five parts per trillion. Our evolutionary ancestors relied heavily on this scent to find fresh water sources during droughts, which explains why almost everyone finds the smell so deeply satisfying and nostalgic. We literally possess a highly evolved biological tracking system for identifying bacterial byproducts on wet dirt, which we now mostly use to decide if we want to cancel our weekend plans and stay inside watching streaming services!