"Soil is life" my friend and colleague Dr. Lito Arocena used to say.
Soil is an interface between solids, liquids, and gases. It bridges the gap between organic and inorganic. It is the material from which living organisms derive their nutrients.
It is much more than just dirt.
Indeed, a dictionary definition of "dirt" is not particularly flattering: "a substance, such as mud or dust, that soils something." Dirt is displaced soil.
The definition for soil is much more inspiring: "the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay and rock particles."
Soil serves four fundamental purposes. The most obvious is as a medium for the growth of plants but it also purifies and stores water, it modifies the atmosphere, and it serves as a habitat for countless organisms.
The layer of soil beneath our feet is not very thick, ranging from
10 centimetres to a couple of metres deep. Looked at from a planetary perspective, the soil covering the continents is not even as thick as the skin on your body.
It is a fine layer.
Yet it is in this very fine layer we find complex chemistry, phenomenal physics, and beautiful biology along with geology, ecology, and any number of other disciplines.
Soil is a rich microcosm, alive with billions of creatures. Arguably, there is more life underground than above.
Indeed, if it wasn't the middle of winter and the ground wasn't frozen, you could grab a handful of soil from your backyard and there would likely be more organisms in that one handful than there are people on Earth. Even in the middle of winter, soil is alive with microbial action. A few feet down, soil is busy with a rich myriad of interactions between creatures.
Many soil scientists and ecologists have garnered an army of graduate students with the sole intent of cataloguing all of the creatures in a plot of land. It is a noble quest but ultimately one doomed to futility. A single square yard of rich soil from a forest or grassland can lead to uncovering too many organisms to count.
There could be as many a billion nematodes - microscopic roundworms - within a single cubic metre of soil. The number of common earthworms can range from a few dozen to several hundreds. Somewhere between 100,000 and 500,000 insects could be present although some might be so small that they can only be seen by a microscope.
Then there is the astronomical number of fungi, single-celled bacteria, protozoa, and other creatures that don't fall into these major groups. Many defy description and have never been seen before. Estimates range from 5,000 to 50,000 or more species within a given plot.
This rich biota, though, is only half the story. Soil is a colony of living creatures but it is also the source of nutrients for both its inhabitants and the creatures above. Roots penetrate soil to draw both water and a host of chemical species into plants. There are whole ecosystems operating within the interface between plants and soil. Indeed, there are whole ecosystems operating at all of the interfaces in soil.
Interfaces are an intriguing aspect of soil. Soil is a living material with both where biological and non-biological changes occur at the interfaces. Physical and chemical weathering, along with chemical transformations, are constantly changing the base materials into new soil while maintaining a form of homeostasis.
The levels of some metals in soil are controlled by processes of desorption and adsorption from mineral deposits. Physical weathering can break rock down but it is chemical reactions that dissolve the granular pieces. When the concentration drops in soil water, rocks dissolve. If the concentration is too high, compounds precipitate and new particles are formed.
This balancing act ensures the concentrations of minerals, such as calcium and iron, is relatively constant. Plants absorb these minerals resulting in more dissolution which has long term effects. At the same time the decay of dead material and the weathering of rocks can add calcium and iron to the soil.
The interplay between physical transport and chemical transformation means that soil is not a static material. It is constantly changing.
Then there is water which plays such a huge role in our environment. Water and air channels in soil typically make up 50 per cent of the volume. The two are in balance; as water increase, air decreases and vice versa. Both are essential to maintain both plants and other organisms in the underground world.
My friend Lito spent his life pursuing an understanding of the world beneath us. He had a contagious enthusiasm for soil and all it represents.
I will miss him.
