The world’s agricultural dirt is getting sicker, according to Montgomery and Biklé. In their book The Hidden Half of Nature: The Microbial Roots of Life and Healththey explore the chemicals, worms and microbiomes of the soils of the world’s farms and conclude the human population, although still growing in numbers, is being deprived of good quality food. The usual measure of the health of soil is the amount of nitrogen, phosphorous, potassium (NPK) it contains, and these minerals in soils with the right acid ph may make the plants grow bigger and stronger, but without the many trace elements that we humans need, we have been getting weaker.
We are alive because of a vast number of different species of microbes that live in us and on us. When we observe a natural forest we easily see a great variety of living things that form a complex web of life, but there is just as complex a living community out of sight under the surface, both in the external world and in the internal world of our stomach, small intestine, and large intestine. Each of these have specialized functions, and each has a specialized community of microbiome inhabitants. These have been functioning and evolving ever since life began and are only now being studied in detail.
The Hidden Half of Nature is an easy read backed up with twenty pages of fine-print scientific documentation.