What are the essentials for life? While you might think you can't live without your smartphone or high-speed internet, the truth is that the luxuries of modern life are not what keep us alive. You could easily forgo a beer on Friday or a coffee on Monday. The necessities are much simpler.

So, what truly sustains life?

Most people will point to air, food, and water. You might even add shelter if you're feeling generous. However, if you look a little deeper, you'll uncover a fundamental element that underpins all these essentials.

Soil. Earth. Dirt.

We often overlook it. Although we inhabit planet Earth, we frequently disregard the significance of the soil beneath us, treating it as mere dirt.

It's time to reconsider our approach. After all, we might be walking on something remarkable.

Beneath the surface, moles are busy crafting their tunnels, aerating the ground. Worms, mites, and nematodes feast on decaying organic matter, while resilient tardigrades, resembling tiny bears, hunt for bacteria. Roots dig deep for water, anchoring themselves firmly. Fungi create intricate networks of hyphae beneath our feet. This vast underground mycelium forms a complex ecosystem, contributing to the spongy texture of the forest floor. But be cautious; the fungus is aware of your presence. When you step down, it reaches up in response.

But what exactly is soil? How does it form? And more critically, how does it benefit us?

Join me on a journey as we explore the hidden world beneath our feet.

Layers of Life

Quality soil resembles a decadent chocolate cake. Rich, dark, and crumbly; from above, it may appear uninviting and rough. Yet, slice into it, and you reveal its hidden treasures. Just like cake, soil consists of distinct layers, each known as a ‘horizon,’ which are crucial for understanding the wonders of earth.

Starting from the top, we encounter the ‘O-horizon.’ Nature, like a skilled baker, adorns the earth with leaf litter, decaying plants, and organic debris awaiting decomposition. You might think decomposition is a spontaneous process, but it requires specific conditions. Insufficient moisture can hinder microscopic life, while excessive water can slow decomposition, leading to a buildup of organic matter. This waterlogged, low-oxygen soil resembles a dense brownie rather than cake — we refer to this as peat. If peat sinks deeper into the earth, it can transform into coal through heat and pressure.

Next comes the A-horizon, or topsoil, where a multitude of microorganisms feast on organic matter, breaking it down into nutrients that enrich the soil. Earthworms, arthropods, nematodes, and diverse bacteria thrive in this layer.

In ‘How to Green the World,’ I highlighted the catastrophic consequences of topsoil erosion for agriculture. Civilizations have risen and fallen based on soil health. The Egyptians benefited from the annual Nile floods that rejuvenated their fertile land, while many societies faced deforestation and soil depletion, leading to food scarcity and societal collapse. It’s no wonder soil is often referred to as ‘black gold.’

Change is constant, yet some things remain the same.

Based on 2014 estimates, the world has approximately sixty years of topsoil left. Alarmingly, it takes between 500 to 1000 years to form just one inch of topsoil. Fertilizers are not a solution; much of what we apply merely replaces nutrients lost through erosion. David R. Montgomery, in ‘Dirt: The Erosion of Civilisations,’ explains:

> “This puts us in the odd position of consuming fossil fuels — one of the rarest and most valuable resources — to substitute for dirt — the most accessible agricultural input.”

The situation is dire!

Delving further, we reach the B-horizon, or subsoil, characterized by clay and oxides. It hosts few organisms aside from some resilient bacteria and a few thirsty roots. Historically, people have built adobe and rammed earth structures from this layer. The finest earthen homes are crafted using wattle-and-daub techniques, where thin branches are woven together, and the mixture of subsoil, dung, chalk, or limestone dust is applied. Each village has its unique recipe, often tied to local beliefs. In the historic town of Stratford-upon-Avon, you can still admire medieval wattle-and-daub homes, including the birthplace of Shakespeare.

As we journey further, we encounter the C-horizon, the parent material where soil formation ceases. Few organisms inhabit this layer, and it signifies the end of our exploration into the depths of soil.

A Hidden Habitat

What kind of creatures dwell in the dark, damp soil, feeding on decaying matter? Aside from teenagers, many species do, while you are the rare surface dweller. An astonishing 10,000 to 50,000 species can be found in a single gram of soil. Here are some key players.

First up are bacteria and archaea. These one-celled organisms are often confused, but surprisingly, archaea share a closer genetic relationship with humans than bacteria, having diverged billions of years ago. Despite their differences, they both carry out essential functions crucial for life. For instance, Nitrobacter converts nitrites into nitrates, making inorganic nitrogen accessible to plants. Some bacteria form symbiotic relationships with legumes, creating nitrogen-fixing nodules. Scientists are working to replicate this process by splicing nitrogen-fixing genes into plant-associated bacteria, aiming to reduce our reliance on costly fertilizers. As John Peters notes, “Transforming food production to work without nitrogen-based fertilizers could be a significant advancement for developing nations. Introducing these microbes would be akin to pouring kombucha onto roots.”

Recent years have seen soil bacteria undergoing significant changes due to reclaimed water irrigation. Exposing these bacteria to antibiotic-laden water is inadvertently selecting for superbugs, rendering antibiotics ineffective. This is particularly concerning as many of these bacteria are found in urban soils, too close for comfort!

However, nature may provide a solution: actinomycetes. These organisms are thought to bridge the gap between fungi and bacteria. They are known for producing many of the antibiotics used to combat various diseases. Additionally, they contribute to the distinct ‘earthy’ aroma of healthy soil.

Next, we have fungi, often misunderstood organisms. Unlike animals that digest internally, fungi secrete enzymes into their environment for digestion. Their underground network of hyphae gives rise to various fruiting bodies or mushrooms. Remarkably, four hundred million years ago, giant fungi towered over early plants; the mystery of prototaxites was only solved when these ancient fossils were identified as fungi.

Saprophytic fungi play a crucial role in converting dead organic material into biomass and other essential compounds. If food is left in the fridge too long, they’ll take advantage of it. Meanwhile, parasitic fungi, the more dramatic among them, invade living organisms. The intriguing honey fungus (Armillaria solidipes), resembling something from a fairy tale, has a hidden surprise; a honey fungus in Washington state is recognized as the largest organism on Earth, covering an astonishing 2.5 square miles.

Initially viewed as pests, we now understand that parasitic mushrooms may help eliminate weaker species, allowing ecosystems to thrive.

Finally, we have mycorrhizal fungi, which form symbiotic partnerships with plants. These fungi significantly enhance nutrient uptake, aiding in the absorption of essential elements like phosphorus and zinc, while improving disease resistance.

These fungi possess a remarkable ability: they enable plants to share nutrients among each other. For years, biologists puzzled over how young pine saplings manage to thrive. The answer lies underground; older trees nurture their offspring by transferring sugars through the mycorrhizal network, leading to the concept of the ‘wood wide web,’ where each tree acts as a node in this intricate system.

Plants partnered with these fungi grow healthier and more rapidly. Farmers are beginning to adopt no-till agricultural practices, as traditional tilling disrupts fungal networks, necessitating increased fertilizer use while releasing more CO2 into the atmosphere. No-till methods avoid these issues and can even reduce pesticide use by an impressive 97 percent, fostering greater biodiversity in the soil.

The complex architecture of fungi binds soil, improving porosity, aeration, and water retention, while facilitating the distribution of nutrients. If such technology were invented, it would be a billion-dollar breakthrough, yet fungi provide it at little cost!

The Value of Soil

Given the incredible capabilities of soil, we should cherish it as a precious resource. Instead, we often neglect it, allowing it to become trapped in urban environments, squeezed between concrete and asphalt. Joni Mitchell’s lyrics resonate: “We paved paradise and put up a parking lot.” Consequently, the remaining soils in parks and urban areas have become heavily contaminated.

Polychlorinated biphenyls from paints and sealants can lead to serious health issues, while organochlorine pesticides are linked to neurological damage and endocrine disruption. Brominated flame retardants from plastic waste contribute to cancer and other health concerns. All of these toxins infiltrate urban soils, particularly in industrial areas — a grim consequence of our modern, high-tech society.

Additionally, toxic elements like lead, cadmium, and mercury seep into urban soils, often related to vehicular traffic. Children are especially vulnerable to these exposures, given their tendency to play in the dirt.

Mycologist Paul Stamets advocates for mycoremediation, utilizing mushrooms' natural ability to absorb heavy metals. About two dozen species are hyperaccumulators, drawing heavy metals into their mycelial networks and concentrating them in their fruiting bodies — the mushrooms — which can then be safely harvested and disposed of. Different metals require specific mushroom species; for instance, the common button mushroom (Agaricus biporus) is effective against cadmium, while the shaggy mane mushroom (Coprinus comatus) targets arsenic. Fungi truly are a gift that keeps on giving!

Reviving Our Immune Systems

In the last century, we have isolated ourselves, spending over 90% of our time indoors. This has left our immune systems restless and unchallenged, leading them to react to new stimuli in ways that can be detrimental. Research indicates that decreased microbial diversity may contribute to conditions like asthma and other allergic diseases.

In Finland, the percentage of farmers has plummeted from 17.3% in 1970 to just 4.9% in 2000, paralleled by a rise in allergic rhinitis from 0.1% to 8.9%. Another study published in the New England Journal of Medicine found that exposure to a diverse array of microbes correlates with a reduced risk of asthma. The dirtier a child’s environment, the more robust their immune system appears to be — farm-raised children exhibit the least risk.

The hygiene hypothesis suggests that early exposure to specific microorganisms fortifies the immune system against allergic diseases. A study on neonatal mice found that developing a diverse lung microbiome encourages the formation of regulatory T cells, which combat pathogens and foster tolerance to allergens. Conversely, reduced microbial diversity results in persistently elevated IgE levels, known to trigger allergic asthma.

Professor Nassim Nicholas Taleb introduced the term ‘antifragile’ to describe this phenomenon. Contrary to the instinct to shield children from dirt, we should allow them to engage with nature, which strengthens their immune systems. As the saying goes, a little dirt never hurt anyone.

We must embrace the wonders of soil. For too long, we have kept ourselves clean, observing the natural world from a distance. As Joni Mitchell famously noted, “You don’t know what you got till it’s gone.” It’s time to protect our soils and nurture the organisms that inhabit them. If we fail to do so, we risk severe consequences for our health, food systems, and even our climate. So, let’s dig in and get our hands dirty; like a humble seed, you may find yourself flourishing in the process.

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