The Hidden World Under Our Feet


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So, what are the basics?

At a push, most guess air, food, and water. If you’re feeling decadent, you might throw in some shelter. But, dig a little deeper, and you’ll discover a unifying factor — a mystery candidate — upon which all life’s essentials rely.

We never give it a second thought. It might be called planet Earth, but we don’t think of it that way — in fact, we treat our soils like dirt.

We should tread more carefully. After all, you never know who you might be treading on.

Down under, moles scrape out a living in their tunnels, aerating the underground. Worms, mites and nematodes chow down on the world’s greatest All-You-Can-Eat buffet: an endless meal of the dead and dying. Meanwhile, the indestructible tardigrades, like ferocious microscopic bears, hunt for bacteria. Roots rummage down to find water, riveting themselves to the ground. And fungi weave their wicked webs of hyphae (thread-like filaments of fungi). Beneath each footstep, hundreds of miles of fungal architecture, known as mycelium, exists in a perpetually shifting patchwork. It’s why the forest floor is so spongy. But don’t linger too long, the fungus knows you’re there. When your foot presses down, the fungus reaches up.

But what is soil? How is it formed? And more importantly, what can it do for you?

Come with me now on a journey, as we delve down into the hidden world under our feet.

Caked in Mud
Good soil is a lot like chocolate cake. Deep, rich and brown; crumbly but moist. From above, the ground isn’t much of a looker, too rough and ready, frustratingly opaque. But, cut yourself a slice, and you’ll reveal its hidden secrets. Just like cake, soil comes in layers. Each layer is called a ‘horizon’, and they are essential to understanding the marvels of mud.


From the top, we begin with the ‘O-horizon’. Like an expert baker, nature decorates her cakes: leaf litter, dead plants and animals, and other detritus await decomposition. You might assume decomposition just happens, as if by magic, but like baking it requires precise conditions for the process to occur. Too little water and the microscopic munchers can’t survive. Perfect soil should be moist but add too much water, and the process slows down dramatically, leading to a build-up of organic matter. These low-oxygen, water-logged soils are less like cake, and more like a stodgy brownie — we call this peat. If the peat descends into the oven of the earth, then like my last brownie attempt, it emerges charred black, having formed coal.


Next, is the icing on the cake, the topsoil or A-horizon, where billions of microorganisms dine on organic matter, breaking it down into simple nutrients, enriching the soil. Wiggling through this layer, we find earthworms, arthropods, nematodes, fungi and cacophony of bacteria and archaea.

In ‘How to Green the World’, I warned how the erosion of topsoil is catastrophic for agriculture. Civilisations rise and fall with the soil. Some, like the Egyptians, struck the jackpot; the annual Nile floods replenish the banks of the river, sustaining the deep black colour indicative of fertility. Little wonder Egypt has remained a breadbasket for over four-thousand years. Most weren’t so lucky. Booming populations combined with decreasing soil fertility led to a cycle of deforestation. As the farmlands grew scarcer, farmers took to the hillsides. Denuded and unanchored, topsoil slowed off the slopes and fields, clogging up the irrigation systems. Eventually, food dwindled, and society slid into anarchy and inevitable collapse. It’s no wonder soil is known as the ‘black gold’.

The more things change, the more they stay the same.

Based on trends in 2014, the world had about sixty years of topsoil left. Worryingly, one inch of topsoil can take between 500 to 1000 years to form. Nor is fertiliser the answer; half the fertiliser dumped on soil simply replaces the nutrients we lose from erosion. Writing in ‘Dirt: The Erosion of Civilisations’, David R. Montgomery explains:

‘This puts us in the odd position of consuming fossil fuels — geologically one of the rarest and most useful resources ever discovered — to provide a substitute for dirt — the cheap and most widely available agricultural input imaginable’.
The world’s gone mad!


Delving deeper, we arrive at the subsoil, the B-horizon, an accumulation of clays and oxides. Aside from the odd lonely bacteria and a few thirsty roots, it’s relatively barren. Historically, people built adobe, cob, and rammed earth houses with subsoil. But the best type of earthen house is wattle-and-daub. The wattle is made by weaving thin branches through slates. Next, we make daub by mixing the subsoil with dung, chalk or limestone dust, adding straw for reinforcement. Everyone village and town had their own unique recipe, superstitiously swearing by a particular type of manure or an exact golden ratio of ingredients. Daub is then smeared on the wattle forming the walls and finished with the quintessential white-wash. Visit the historic town of Stratford-upon-Avon in England, and you can still see the glistening medieval wattle-and-daub cottages and houses, including Shakespeare’s childhood home!

Journeying further, we come to the petrous C-horizon, the parent material where the soil stops. Few organisms are kicking about amongst the enriched carbonates which leach down from the top. Like the solemn end of a slice of cake, we’ve reached the plate; we’ve hit rock bottom.

A Place to Call Home
What kind of creature spends its life in the dark and damp munching on decomposing organisms? Teenagers aside, most species do, you’re the weird one surface-dweller. An estimated 10,000 to 50,000 species live in each gram of soil. Here are the big players.

First are the bacteria and archaea. These tiny one-celled critters are frequently confused, but despite their similarities, you might be surprised to learn archaea are more closely related to you and me than their bacterial brothers, diverging billions of years ago. Notwithstanding the family breakup, this odd couple carries out a variety of essential functions without which life as we know it would not exist. The imaginatively named Nitrobacter, for instance, turns nitrites into nitrates, allowing plants to access inorganic nitrogen vital to their everyday functioning. Some bacteria have even teamed up with plants, notably legumes, forming symbiotic nitrogen-fixing nodules. Scientists are attempting to replicate these middle-men, splicing nitrogen-fixing genes into plant-colonising bacteria, reducing our dependence on exceedingly expensive and environmentally damaging fertilisers. As leading researcher John Peters put it, ‘Transforming food production to work without nitrogen-based fertilizers could be a huge development in underdeveloped countries. Adding these microbes would be like pouring kombucha on roots.’

    How soil can save us all

In recent years, soil bacteria have been undergoing a radical makeover, due to the use of reclaimed water for irrigation. By exposing bacteria to water laced with antibiotics, we are inadvertently selecting for superbugs, rendering antibiotics useless. Particularly concerning, is that many of these bacteria lurk in our parks and urban soils. A little too close to home!

However, nature offers a possible solution, the missing link. I’m not talking about Neanderthals, but actinomycetes; believed to be the evolutionary bridge between fungi and bacteria. They are notable for their ability to produce many of the antibiotics used to fight diseases from tuberculosis to whooping cough. As if that wasn’t enough, they also exude the rich and pungent ‘earthy’ smell, which wafts off freshly turned healthy soil.


Next is a bizarre and yet miraculous branch of life. Fungi are the most misunderstood organisms on the planet. Where animals evolved to internalise their digestion, fungi let their bellies hang out, excreting digestive enzymes into their local environment. Characterised by the mesh of hyphae permeating the underground, their fruiting bodies or mushrooms come in a myriad of forms. Amazingly, four hundred million year ago gigantic fungi towered over the primordial plants; prototaxites had been a mystery for decades until someone noticed these monumental fossils were actually fungi.


Saprophytic fungi convert dead organic material into biomass, carbon dioxide and other essential molecules. Leave food too long in the fridge, and they’ll tuck in. Finders keepers. Parasitic fungi, the goths of the bunch, colonise living species such as trees. The musty-brown Lilypad-Esque honey fungus (Armillaria solidipes) seems straight out of Alice in Wonderland. But, don’t judge a book by its cover. Belowground hides a monster: a honey fungus in Washington state is the largest organism on Earth covering an awe-inspiring 2.5 sq miles. Time to lay off the pines.

First considered a pest, we are coming to understand parasitic mushrooms may be nature’s method for weeding out the weak, allowing stressed landscapes to stage a stunning revival. Not so cruel after all.

Last but not least, are the mycorrhizal (meaning mushrooms related to roots) fungi, which form symbiotic relationships with plants. Plants who partner up with fungi, buddy-cop-style, see dramatic increases in the ingestion of nutrients, nitrogenous compounds, and essential elements (such as phosphorus, copper, and zinc) — and they’re better at fighting diseases.

These fungi have a truly magical property. Plants which have access to the fungal network can transfer nutrients from one another. For many years, biologists scratched their heads wondering how young pine saplings got enough light to photosynthesise and grow. The secret was belowground. The elder trees were looking after their offspring, gifting sugars via the mycorrhizal fungi. This phenomenon led to the system being named the ‘wood wide web’, each tree functioning as a node in the network.

Plants inoculated with these fungi are healthier and grow quicker. Farmers are tapping into this natural technology by switching to no-till agricultural methods. Constant tilling of soil destroys fungal networks, increasing the need for fertilisers while releasing more CO2 into the atmosphere — ploughing the stubble of the last harvest into the ground releases 41 per cent more carbon dioxide. No-till has none of these downsides, and can even cut pesticide use by 97 per cent, increasing the biodiversity of soil, including beneficial organisms like earthworms and beetles. Though initial yields may reduce 10 to 20 per cent, we see a subsequent rebound of 15 per cent as the soil adapts.

The intricate fungal architecture binds soil together increasing soil porosity, aeration, water retention, and providing a platform for other lifeforms. All while distributing nutrients within an ecosystem. If you invented a tech equivalent, you’d be a billionaire, but fungi are practically free!

Down and Dirty
Considering the wonders soil can accomplish, we should revere it like the holy grail. Instead, dirt is ground into the cracks, squeezed into the crevices between the concrete and tarmac. ‘We paved paradise,’ sang Joni Mitchell. ‘And put up a parking lot.’ As a result, the soils which still lurk in our parks, school fields and brownfields sites have become heavily contaminated.

Polychlorinated biphenyls from paints, joint sealants and waste combustion lead to neurotoxicity and thyroid disorders. Organochlorine pesticides cause neurological damage, endocrine disorders and high blood pressure. Brominated flame retardants from discarded plastic and chemical and building materials increase the risk of cancer, diabetes, neurobehavioral and developmental disorders, thyroid disorders, and low fertility. They all sink into our urban soils, especially in industrial cities — the sorry price of the modern belching, groaning high-tech economy.

On top of that, toxic elements including lead, cadmium, chromium, mercury, and arsenic permeate urban soils, frequently associated with road traffic — as metallic particles, from cars and lorries, rain down upon the ground. Children are particularly vulnerable to exposure, especially given their propensity for rolling in the mud.

Mycologist Paul Stamets advocates mycoremediation, utilising the bioaccumulative properties of mushrooms. About two dozen species are ‘hyperaccumulators’, sucking up heavy metals via the mycelial network, and concentrating it in the fruiting body — the mushroom — which can be picked and safely destroyed. Each metal requires a different species: the common button mushroom (Agaricus biporus) is suitable for cadmium, whereas the wonderfully named shaggy mane mushroom (Coprinus comatus) prefers arsenic. Fungi are the gift which keeps on giving!


Our Immune System is Bored
In the past hundred years, we’ve entombed ourselves, spending more than 90% of our lives inside. As a result, our immune systems have become restless and bored, unable to play, as they once did, with the soil microbes next door. Like a grounded kid, they’ve found new toys to play with, annoying us all in the process. Researchers have proposed reduced microbial biodiversity as a cause for conditions such as asthma alongside other atopic diseases.

In Finland, the proportion of farmers has decreased dramatically from 17.3% in 1970 to 4.9% in 2000. Concurrently, allergic rhinitis (hay fever) increased from 0.1 to 8.9%. Another study published in the New England Journal of Medicine found that diversity of microbial exposure was inversely related to a risk of asthma. The filthier you were as a kid, the healthier your immune system — kids born on the farm had the lowest risk of all.

The ‘hygiene hypothesis’ states that early childhood exposure to particular microorganisms protects against allergic diseases by contributing to the development of the immune system. A study in neonatal mice reported that the formation of a complex lung microbiome induced regulatory T cells (a ‘killer cell’, deadly to pathogens), promoting tolerance to house dust mite allergens. In contrast, reduced microbial diversity led to long-lasting elevated levels of IgE — a type of antibody known to cause allergic asthma.

Professor Nassim Nicholas Taleb coined the term ‘antifragile’ to describe such a phenomenon. Counter to the instinctual urge to wrap children up in cotton wool, protecting them from danger; we must do the opposite, letting them get dirty, ensuring they get a healthy dose of bacteria. Our immune systems only get stronger by being tested; left to their own devices, they run wild. As the saying goes, a little dirt never hurt anyone.

We should all be embracing the wonders of the soil. For too long, we have kept our hands clean, observing nature from a distance. But, as Joni Mitchell said, ‘you don’t know what you got till it’s gone’. We need to start protecting our soils and nurturing the creatures that live in them. If we don’t, we face calamitous consequences, ranging from our health, food and even the climate. So, get stuck in. Get down and dirty, and like the humble seed, you might be surprised to find you grow too.