The world beneath our feet


Colin Tudge reflects upon Bruce Ball’s latest book, Healing Soil

Truly the things we take for granted – like the Earth, and indeed life — are the most wondrous. Nothing is more taken for granted — and routinely abused — than soil; and yet, as Bruce Ball illustrates in his latest book, Healing Soil, the realities of soil as now being revealed by modern science are beyond exhaustive understanding, and the practical, social, political, and metaphysical ramifications are endless. If we wanted to create a university that was truly universal, embracing all faculties, we could very reasonably put the study of soil right at the heart of it.  

Soil begins simply enough – as bedrock. Different bedrocks produce different soils. The bedrock is then broken down by water and ice and wind, and alternating heat and cold, and interacts chemically with whatever happens to be in the atmosphere, to produce sand, silt, and clay in varying proportions. A key game-changer was and is “free” oxygen gas, as first began to be produced in the ocean in significant quantities about two billion years ago by single-celled diatoms, which had invented a new form of photosynthesis that splits water and so releases oxygen. Oxygen gas is super-reactive, and transforms almost everything it comes in contact with, including bedrock. 

But as Bruce describes, broken-down bedrock, whether or not transformed by oxygen, is not soil. What makes it soil is or are the living creatures that successively invade and alter the mineral base. All three domains of life are represented in super-abundance: the Bacteria and Archaea, which are the simple-celled prokaryotes, aka microbes; and almost though not quite all the kingdoms of the eukaryotes, the creatures with complex body cells. These include the fungi, various kingdoms of “protists” (single-celled eukaryotes, including “protozoa”), plants, and a huge array of animals from almost every known phylum, including some phyla that only a few biologists have even heard of. Nobody knows how many different species or types there are living in the soil and this can never be known precisely, but there must be tens of thousands, probably hundreds of thousands. The number of individual organisms boggles the mind. An oft-quoted stat tells us that each teaspoonful of fertile soil – about one gram – may contain a billion microbes; which means there are as many microbes in 100 grams, less than four ounces, as there are stars in the Milky Way. Very large numbers are often said to be “astronomical”. But the biggest numbers of all are biological. That’s one reason why natural selection works as well as it does. There’s a lot to choose from. 

Although there is endless strife between the different organisms (protozoa and nematodes eat bacteria and fungi, and some fungi trap and digest nematodes), in the end the myriad creatures all work together and between them they break the bedrock down still further and then transform the mineral particles into soil; a common resource that benefits them all.  For bona fide soil is a miracle of micro-architecture, a three-dimensional labyrinth, in which the mineral fragments are mortared together by the dead and living bodies of the soil-dwelling organisms and the many and various organic molecules that they exude and secrete. 

As Bruce Ball describes, the microarchitecture that is most suitable for most living creatures, including the roots of most plants, is 50 per cent mineral and 50 per cent space, and the space, ideally, at any one time, is filled with 50 per cent water and 50 per cent air. But too much mechanical disturbance, excess fertilizer, pesticide and herbicide and miscellaneous toxins kill off the living creatures, and heavy machines crush the microarchitecture, and so reduce this delicate 3-D mega-city to what American farmers in the over-stretched mid-West call “dirt”.  Bruce is very concerned with the practicalities, and has done much to develop what he calls “a simple spade test for The Visual Evaluation of Soil Structure aka VESS”. Simply by looking at soil, and feeling and squeezing it, a farmer can get a very fair insight into its physical state which in turn reflects and influences the essential biota. Farmers worldwide of many kinds in many different settings have shown that the spade test works and is most helpful. Bruce has illustrated all this with photographs from around the world and also with his own quasi-technical and quasi-abstract paintings (who else paints soil micro-architecture?) — for he is not only a soil scientist (based at the Roslin Institute, Midlothian) but also a poet and an artist. Healing Soil is as nice combination of science and lyricism. 

The non-antagonistic relationships between the different organisms are not simply those of adaptation and tolerance but of true mutualism: symbiosis that brings benefit to all players. Thus in a pristine soil, the roots of plants further enhance their own wellbeing by exuding large quantities of organic molecules that encourage the bacteria and fungi that keep the essential architecture intact. Wide-ranging fungal hyphae of the kind known as mycorrhizas link plant to plant so that most or all of the trees in a mature wood, plus their fungal companions, in effect form one great superorganism, albeit composed of several or many hundreds of different species. The idea beloved of cavalier councillors and entrepreneurs that we can simply replace ancient forests that may be in the way of highways and super-trains with a commensurate area of saplings, is the grossest nonsense. But from the bureaucrats’ perspective it is not “realistic” to think ecologically. Ecology is for hippies. If such thinking continues to dominate, we’ll all have had our chips. 

For in practice, as Bruce points out, soil is the mother of all terrestrial life. No soil, no land plants; and without land plants, no land animals, which of course means no us; and probably, if we, human beings, had not evolved the way we did, in trees and in the savannah, then no Earthly creature would have undergone the co-evolution of brain and hand which led to human-style intelligence. So it is that squids, octopuses, and cuttlefish are bright but stuck as they are at the bottom of the sea (although octopuses venture on to land now and again) none of them ever evolved into poets or physicists or professors of jurisprudence, or is likely to. The sea just doesn’t seem to offer the right impetus or opportunities for such refinements to come about. (On the other hand, cephalopods first evolved more than 500 million years ago and the modern groups with their impressive cognitive skills first appeared more than 400 million years ago — and they are still with us. The genus Homo with its shamans and philosophers and think tanks and technologists at most is two million years old and our own genus Homo sapiens is less than a million years old and we’re already staring Armageddon in the face. There’s a moral in there somewhere). 

It is not true, however, as some enthusiasts are wont to suggest, that soil is the mother of all life on Earth. For the evidence suggests that microbial life of a kind first arose on Earth in land-based puddles or perhaps in submarine hot springs around 3.7 billion years ago, and the stuff that can properly be called soil did not properly begin to form till billions more years had passed and marine life was already abundant and diverse. To be sure, land in the form of bedrock and later in the form of soil, and the terrestrial creatures that have evolved on land, have profoundly affected ocean life in many different ways. Minerals from the land – salt, nutrients, and these days toxins – have been enriching (or poisoning) the seas since the year dot, and many of the creatures that now are key players in marine ecosystems evolved on land, from the whales and seals to mangroves to the sea-grasses that feed dugongs and much else besides. But most of the creatures that now live in the sea arose in the sea, including the fish and most of the invertebrates, and ocean-bound creatures would surely abound in great variety even if there was no terrestrial life at all, or indeed no land at all. (Though land is physically useful too because it interrupts the ocean currents and causes turbulence which stir up the vital nutrients). 

Presumably – how could it be otherwise? – prokaryotes and (single-celled?) fungi must have come on to land billions of years ago. But – probably – for many millions of years they would simply have formed a slime on wet rocks. The first known multicellular, eukaryotic, bona fide terrestrial creatures evidently arose around 475 million years ago: plants of the grade generally known as “bryophytes”, represented today by liverworts, hornworts, and mosses. Bryophytes don’t have formal internal plumbing, in the form of vessels, to carry water and nutrients rapidly and efficiently around the plant. So they were and are doomed to remain small. Plants that do have vessels – the tracheophytes – did not appear in the fossil record until around 400 million years ago – and plants with vessels may become very large indeed. More to the point, in this context, is that bryophytes don’t have proper roots. Essentially they just cling to the surface. But tracheophytes do have roots, which sometimes probe very deep and spread very wide, their range and influence extended by their mycorrhizal symbionts; and the root-fungus combination has huge penetrative power. Once roots had evolved, soil-building could begin in earnest. It’s taken a long time – 400 million years – to create the depth and ecological richness of modern soils. But 400 million years is only around one tenth of the total time that life has existed on Earth. 


All this triggers further thoughts. For example: 

1: Soil science must be taken very seriously. Of course it is already taken very seriously in some circles — but it is not yet a popular pursuit, and one of the virtues of Healing Soil is to show why it ought to be. Once you are alert to the variety and intricacy of soil it becomes very intriguing indeed. Certainly, to ride rough-shod over well-formed soil, to pollute and crush it or simply sweep it aside, is philistine going on suicidal, although in the most influential circles it is the norm. The 1960s’ entrepreneur Jim Slater used to say that you should never put your money into a company that doesn’t have an accountant on the board – or into a company that has more than two accountants on the board. Similarly, we should never trust a government that has no ecologists, or relies on ecologists who are paid by corporates. The economy must be geared to the ecology. Economies are arbitrary but ecology is real.  

2: The science of ecology needs to extend its traditional range – which indeed is happening. A key idea to emerge in the past few decades is that of the keystone species – particular species or groups of species that set the tone of the whole ecosystem. Part of this is the realization that the apex predators are not merely added on to and dependent upon the herbivores on which they prey and therefore on the plants that the herbivores feed upon. Studies in particular of wolves in Yellowstone, newly returned after some decades’ absence, show that the wolves influence the behaviour of the deer that they hunt and eat and the deer’s behaviour in turn largely determines what plants may grow and where. Thus the ecosystem is controlled from the top down and not simply from the bottom up as common sense suggests and was traditionally supposed.  

But the opposite is also true. For ecosystems are not shaped simply by the visible creatures but at least equally by the ones that are too small to see without a microscope, including the microbes of the soil but also including viruses, which invade all other creatures, including the microbes. Viruses are key players not simply because they kill other organisms (and so help for example to regulate the populations of microbes) but as nature’s genetic engineers, profoundly affecting the behaviours of all genomes. Vitally, though, the virus-altered genomes are then subject as everything is in nature to natural selection – so the induced alterations that reduce viability for the most part are weeded out. Nature does not select, as human biotechnologists do, for very particular traits that may reduce the viability of the whole. A key difference.  

3: Perhaps the biggest lesson of all is that the relationship between the mineral base of the soil and the life of the soil is that of a positive feedback loop. The fragmented bedrock supports the living creatures which then transform the mineral substrate in ways that benefit life itself. And this, the positive feedback loop, is a key feature of Gaia, the worldview first proposed in the 1960s by James Lovelock which says that in the end, for all the internecine conflict, life and the fabric of the Earth itself operate as if to form one great organism.  Even more broadly, we might say (although I am not sure that Lovelock did say) that despite the prevailing dogma, and despite appearances, life in the end is more cooperative than it is competitive. If it were not so, then life would be impossible. Each living cell demonstrates the truth of this, for each is a master-class in cooperativeness. All ecosystems and Gaia as a whole show the truth of this too. Politicians and economists and even some moral philosophers have often argued that the ultra-competitive economy reflects what happens in nature, and therefore is natural, and therefore is inevitable, and we might as well get used to it. In the prevailing neoliberal economy this point of view is taken to extremes. This as I have said many a time and oft is bad biology and as moral philosophy is even worse. (Peter Kropotkin said the same thing more than 100 years ago). 

 4: In similar vein, Bruce Ball suggests that the communities of the soil – highly diverse, not without antagonisms, but in the end cooperative and creative – may serve as a fine model for human communities. Why can’t humanity be more like soil?  

5: But all the biggest ideas in the end are rooted in metaphysics which also underpins all religion. In metaphysical vein it seems that most people through most of history and prehistory, right up to the present, feel deep down in their bones that there must be some intelligence, consciousness, mind, behind the universe. Nothing as complex and as intricately interdependent as our Earthly ecosystems could have come about just by chance, could it? Or even just by chance shaped by natural selection? 

We need not suppose that this hypothetical “mind” is anything like what goes on in our own heads. What we experience as mind is merely our mind’s impression of the mind that’s already out there – just as what we see and take to be reality is really our brain’s interpretation of the particular electro-magnetic signals to which our retinas are sensitive. Metaphysicians and theologians of various hues have been asking for many hundreds of years whether this hypothetical mind should be seen as a part of the fabric of the universe — a “universal mind” which some equate with God; or is supplied by a Creator God who is separate from His (or Her or Its) Creation; while theologians of the kind known as panentheists suggest that it’s a bit of both. (Others yet again say that God, properly conceived, is not a hands-on creator at all. Rather, He, She or It is what makes it possible for anything at all to exist; a thought encapsulated by the word “source”). 

But people of the kind we might call “hard-nosed” argue or simply assert that all such speculation is mere whimsy. They compare God, or the universal mind, to fairies at the bottom of the garden. Some prominent scientists argue this – although a great many of at least equal stature do not. Nobody knows or can ever know which kind of idea comes closest to the truth but neither seems entirely convincing. The principal hard-nosed argument when you boil it down is that modern science allows us to frame an explanation of life, the Earth, and everything that is, simply by appealing to the laws of physics and to natural selection. (Scientific “law” is itself a strange concept but we’ll that pass). Yet as pointed out elsewhere on this website, the laws of physics are not and never can be certain. As Karl Popper pointed out in the middle of the 20th century, all scientific theories in the end are conjecture (his word). We must always fall short of the lawyers’ demand – for “the truth the whole truth, and nothing but the truth”. In any case the explanations provided by science alone, wondrous though they often are, leave a lot of loose ends – including the apparent, extraordinary unlikeness of “the Goldilocks effect”: that, given the vagaries and the extremes of the universe, the chances of producing a world like ours capable of supporting life which is innately both complex and fragile, seem vanishingly small. Some scientists have tried get round this problem by appealing to natural selection. They suggest that in truth there are countless universes but natural selection ensures that the only ones that survive are the most viable, including our own Milky Way, and our astonishingly unlikely Earth. 

In the end, though, the hard-noses, for all their apparent rigour, rely on an argument that simply doesn’t stand up: that because it is possible (fingers crossed, and taking a great deal on trust) to explain the universe to some people’s satisfaction without appeal to a guiding mind (whether or not that mind is called “God”) that therefore there is no guiding mind. But there is no “therefore”. Even if there were no loose ends in the strictly materialist explanation of the universe that still would not preclude the possibility that the whole caboodle is guided by some imminent or extraneous mind. And just as the hard-noses like to ask, as if it was the clincher, “who made God?” so we might ask, “How come the laws of physics are as they are? How come these ‘laws’, applied to the energy/matter that is the material stuff of the universe, are of such a kind that in the fullness of time they could produce oak trees, or elephants, or us?” In fact, both sides can ask much the same question – “How come?” — and in both cases it’s unanswerable. You pays your money and you takes your choice. 

It seems to me, though, albeit perhaps whimsically, that the science of soil adds an intriguing dimension to this discussion. Because, as outlined above, unless there was soil there would be no bona fide plants (though some taxonomists class green seaweeds as plants) and no land animals and, almost certainly, no Earthly creatures with intelligence to match ours. But is soil itself inevitable? What law whether scientific or divine says that bedrock, pure mineral, must or even could be degraded and altered in ways that lead to soil? In practice, after all, soil does not become soil until and unless bedrock is transformed by living creatures, and Earth’s creatures evidently were in no hurry to bring about the necessary transformation. Indeed, it seems, living creatures did not start turning rock into soil until they had already been evolving in the seas for at least two billion years. Furthermore, the creatures that helped to make soil must have co-evolved with the soil itself. That is, the ancestors of the soil-makers must have existed before the soil itself came into being but the creatures that live in the soil now and continue to create and maintain its architecture have all evolved in the soil. 

So, to re-state the age-old question in a nutshell, did some Creator God have it in mind from the outset to produce some creature like us that can do science and is able at least up to a point to appreciate God’s endeavours, or did we just come about, as one thing led to another? Soil science does not provide an answer (nothing can) but it does suggest an intriguing new spin. 

Colin Tudge, March 29 2023. 

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