What essentials do we need to survive? While you might argue that your smartphone or fast internet are necessities, they are far from critical. You could easily forgo that Friday night drink or the Monday morning caffeine fix. In essence, the luxuries of life are not truly essential.

So, what are our basic needs?

Most would quickly say air, food, and water. If you want to indulge, you might include shelter. However, a closer examination reveals an underlying element that all essentials depend upon.

Soil. Earth. Dirt.

We often overlook it. Although we refer to our planet as Earth, we seldom consider it in that context—more often treating our soils with disdain.

We ought to be more mindful. After all, you never know what lives beneath your feet.

Underground, moles create tunnels that aerate the earth. Worms, mites, and nematodes feast on a never-ending buffet of organic matter. Meanwhile, resilient tardigrades, akin to microscopic bears, hunt for bacteria. Roots delve deep to access water, anchoring themselves firmly. Fungi spread their intricate networks, known as mycelium, a vast tapestry existing beneath every step we take. This is why forest floors feel so soft. But be cautious; the fungi are aware of your presence. When you step down, they respond.

But what is soil? How does it form? More importantly, what can it provide for you?

Join me on a journey to explore the concealed world beneath our feet.

# Caked in Earth

Quality soil resembles chocolate cake. Rich, dark, and crumbly yet moist. From a distance, the ground may not appear appealing, rugged and unrefined, but slice it open, and you'll uncover its secrets. Like cake, soil has layers, each known as a ‘horizon’, crucial for understanding the wonders of earth.

At the top lies the ‘O-horizon’. Nature, like a skilled baker, adorns her creation with leaf litter, decaying plants and animals, and other organic debris awaiting breakdown. You might assume decomposition occurs automatically, but it requires specific conditions to thrive. If there’s too little moisture, microorganisms struggle to survive. Ideal soil should be damp, but excess water slows decomposition, leading to organic matter accumulation. These low-oxygen, water-saturated soils resemble not a cake but a dense brownie—this is known as peat. If peat sinks deeper into the earth, it may transform into coal, just like an overcooked brownie.

Next comes the icing on the cake, the topsoil or A-horizon, where billions of microorganisms thrive, breaking down organic matter into vital nutrients that enrich the soil. In this layer, earthworms, arthropods, nematodes, fungi, and a multitude of bacteria and archaea coexist.

In ‘How to Green the World’, I highlighted how topsoil erosion threatens agriculture. Civilizations rise and fall based on soil health. The Egyptians, for instance, were fortunate; the annual floods of the Nile replenished its banks, fostering the fertile black soil that has supported them for over four thousand years. Others were not so fortunate. With increasing populations and declining soil fertility, deforestation cycles ensued. As farmland diminished, farmers moved to hilltops, where the unanchored topsoil washed away, clogging irrigation systems. Eventually, food became scarce, leading to societal collapse. It’s no surprise that soil is often referred to as ‘black gold.’

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

Based on 2014 trends, the world has roughly sixty years of topsoil left. Alarmingly, it takes between 500 to 1000 years for just one inch of topsoil to develop. Chemical fertilizers are not the solution; half of what is applied merely replenishes nutrients lost to erosion. In ‘Dirt: The Erosion of Civilizations’, David R. Montgomery notes:

> “This places us in the peculiar position of using fossil fuels—one of the rarest and most valuable resources—to substitute for dirt—the cheapest and most readily available agricultural input imaginable.”

The world has indeed gone awry!

Digging deeper, we encounter the subsoil, the B-horizon, composed of clays and oxides. This layer is relatively barren, home to a few lonely bacteria and thirsty roots. Historically, subsoil was used in constructing adobe, cob, and rammed earth homes. The best earthen construction is wattle-and-daub, created by weaving thin branches and applying a mix of subsoil, dung, chalk, or limestone dust, reinforced with straw. Every village had unique recipes, often involving specific types of manure or precise ingredient ratios. The daub was applied to the wattle framework, creating walls finished with traditional whitewash. In Stratford-upon-Avon, England, you can still admire the medieval wattle-and-daub homes, including Shakespeare’s childhood residence!

As we journey further down, we reach the rocky C-horizon, the parent material marking the end of soil. Here, few organisms exist among the enriched carbonates that filter down from the surface. Like the last morsel of cake, we’ve reached the rock bottom.

# A Home for Many

What creature thrives in darkness, munching on decomposed matter? Aside from teenagers, many species do; you, as a surface dweller, are the odd one out. An estimated 10,000 to 50,000 species inhabit each gram of soil. Here are the key players.

First, we have bacteria and archaea. These minuscule, single-celled organisms are often confused. Despite their similarities, archaea are more closely related to humans than bacteria, diverging billions of years ago. Regardless of their differences, both perform essential functions crucial for life as we know it. The aptly named Nitrobacter, for example, converts nitrites into nitrates, enabling plants to utilize inorganic nitrogen vital for their survival. Some bacteria even form partnerships with plants, notably legumes, creating nitrogen-fixing nodules. Scientists are working to replicate this symbiosis by transferring nitrogen-fixing genes into bacteria that colonize plants, reducing reliance on costly and environmentally harmful fertilizers. As researcher John Peters remarked, “Transforming food production to operate without nitrogen-based fertilizers could revolutionize agriculture in developing nations. Introducing these microbes would be akin to adding kombucha to plant roots.”

Recently, soil bacteria have been significantly impacted by the use of reclaimed water for irrigation. By exposing these bacteria to antibiotic-laden water, we inadvertently select for superbugs, rendering antibiotics ineffective. This is particularly alarming as many of these bacteria reside in our parks and urban soils—too close for comfort!

Fortunately, nature offers a potential remedy—the missing link. I refer not to Neanderthals but to actinomycetes, thought to be the evolutionary bridge between fungi and bacteria. They are notable for producing many antibiotics used to combat diseases like tuberculosis and whooping cough. Furthermore, they exude the rich, earthy aroma associated with healthy, freshly turned soil.

Next, we encounter a peculiar yet miraculous life form: fungi. They are among the most misunderstood organisms on Earth. Whereas animals evolved to digest internally, fungi digest externally, releasing enzymes into their environment. Characterized by an underground network of hyphae, their fruiting bodies, or mushrooms, come in a vast array of shapes. Remarkably, four hundred million years ago, gigantic fungi overshadowed early plants; the prototaxites had long puzzled scientists until they recognized these colossal fossils were, in fact, fungi.

Saprophytic fungi convert decayed organic matter into biomass, carbon dioxide, and other essential compounds. Leave food in the fridge too long, and they’ll happily consume it. Parasitic fungi, the goths of the fungi world, colonize living organisms like trees. The rather whimsical honey fungus (Armillaria solidipes) appears straight out of a fairy tale. But don’t be deceived; below ground lurks a giant: a honey fungus in Washington state is the largest organism on Earth, spanning an astonishing 2.5 square miles. Time to give the pines a break.

Initially considered a nuisance, we are beginning to realize that parasitic mushrooms may play a role in natural selection, allowing stressed ecosystems to rejuvenate. Not so cruel after all.

Last but not least are the mycorrhizal fungi, which establish symbiotic relationships with plants. Plants that collaborate with fungi witness significant increases in nutrient absorption, nitrogen intake, and crucial elements like phosphorus, copper, and zinc—and they become more resilient against diseases.

These fungi possess a remarkable ability: plants connected to the fungal network can share nutrients. For years, biologists puzzled over how young pine saplings acquired enough sunlight for growth. The answer lay underground: mature trees were nurturing their young, delivering sugars through mycorrhizal fungi. This interconnected system earned the nickname the ‘wood wide web,’ with each tree acting as a node in the network.

Plants inoculated with these fungi exhibit better health and faster growth. Farmers are tapping into this natural technology by adopting no-till farming methods. Constant soil tilling disrupts fungal networks, increasing the need for fertilizers and releasing more CO2 into the atmosphere—plowing the remnants of the last harvest into the ground releases 41% more carbon dioxide. No-till methods avoid these pitfalls and can even decrease pesticide use by 97%, enhancing soil biodiversity and fostering beneficial organisms like earthworms and beetles. While initial yields may drop by 10 to 20%, we observe a subsequent rebound of 15% as the soil adapts.

The complex architecture of fungi binds soil, improving porosity, aeration, and water retention while creating a foundation for other life forms. If you were to invent a technological equivalent, you'd become a billionaire, but fungi come at little to no cost!

# Down and Dirty

Given the incredible capabilities of soil, we should cherish it as a precious resource. Instead, dirt is often crushed underfoot, relegated to the cracks between concrete and asphalt. “We paved paradise,” sang Joni Mitchell. “And put up a parking lot.” Consequently, the soils still found in our parks, school fields, and brownfields have become heavily polluted.

Polychlorinated biphenyls from paints, sealants, and waste incineration contribute to neurotoxicity and thyroid issues. Organochlorine pesticides cause neurological damage, endocrine disruptions, and hypertension. Brominated flame retardants from discarded plastics and construction materials heighten the risks of cancer, diabetes, developmental disorders, thyroid dysfunction, and reduced fertility. These contaminants seep into urban soils, particularly in industrial areas—the unfortunate cost of a high-tech economy.

Additionally, toxic elements such as lead, cadmium, chromium, mercury, and arsenic infiltrate urban soils, often linked to vehicle traffic—metallic particles from cars and trucks settle onto the ground. Children are especially vulnerable to exposure, given their tendency to play in the dirt.

Mycologist Paul Stamets promotes mycoremediation, leveraging the bioaccumulation capabilities of mushrooms. Approximately two dozen species are ‘hyperaccumulators,’ capable of absorbing heavy metals through their mycelial networks and concentrating them in their fruiting bodies—the mushrooms, which can then be harvested and safely disposed of. Each metal has a specific species: the common button mushroom (Agaricus biporus) is effective for cadmium, while the whimsically named shaggy mane mushroom (Coprinus comatus) is suited for arsenic. Fungi truly are a continuous gift!

# Our Immune System is Bored

Over the past century, we’ve confined ourselves, spending over 90% of our lives indoors. Consequently, our immune systems have grown restless, unable to engage with the soil microbes that were once a part of our lives. Like a bored child, they’ve turned to new "toys," often causing us trouble. Researchers suggest that diminished microbial diversity may be a contributing factor to conditions like asthma and other atopic diseases.

In Finland, the proportion of farmers plummeted from 17.3% in 1970 to 4.9% in 2000. Concurrently, the incidence of allergic rhinitis (hay fever) surged from 0.1% to 8.9%. Another study published in the New England Journal of Medicine indicated that greater microbial diversity was inversely related to asthma risk. The messier you were as a child, the healthier your immune system—kids raised on farms had the lowest risks.

The ‘hygiene hypothesis’ posits that early exposure to specific microorganisms shields against allergic diseases by aiding immune system development. A study involving neonatal mice revealed that a diverse lung microbiome stimulated regulatory T cells (which combat pathogens), promoting tolerance to house dust mite allergens. In contrast, diminished microbial diversity resulted in persistently elevated levels of IgE—a type of antibody linked to allergic asthma.

Professor Nassim Nicholas Taleb coined the term ‘antifragile’ to describe this phenomenon. Contrary to the instinctive urge to shield children from dirt, we should encourage them to play freely, embracing the chance to get dirty and ensuring they receive a healthy dose of bacteria. Our immune systems strengthen through challenges; left unchecked, they can become overactive. As the saying goes, a little dirt never hurt anyone.

We should embrace the wonders of soil. For too long, we have kept our hands clean, observing nature from afar. However, as Joni Mitchell pointed out, “You don’t know what you’ve got till it’s gone.” We must begin to protect our soils and nurture the organisms that dwell within them. Failing to do so could lead to dire consequences for our health, food systems, and even our climate. So, roll up your sleeves, get your hands dirty, and like a humble seed, you may be surprised at how you flourish.

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