A single teaspoon of healthy soil contains more organisms than humans on Earth

A gram of healthy agricultural soil contains up to 1 billion bacteria, 100 million actinomycetes, 100,000 fungi, 10,000 algae, and thousands of protozoa and nematodes. A single teaspoon (5 grams) may contain more living organisms than the total human population on Earth. These organisms cycle nutrients, decompose organic matter, fix atmospheric nitrogen, and suppress plant pathogens. Industrial agriculture — with its tillage, compaction, and pesticide use — can reduce this biodiversity by 50–90%. Soil scientists estimate that it takes 1,000 years to generate 1 centimetre of topsoil naturally.

Source: Bardgett & van der Putten, Nature (2014)