Beneath every forest floor, desert, and meadow lies one of Earth's most vital—and least visible—circulatory systems. Researchers have now mapped it for the first time, revealing that arbuscular mycorrhizal fungal networks span approximately 110 quadrillion kilometers across the planet, a distance so vast it challenges human comprehension. The finding, published in Science by an international team working with the Society for the Protection of Underground Networks (SPUN), represents a watershed moment in understanding how life itself is sustained from below.
Mycorrhizal fungi form symbiotic partnerships with roughly 70 percent of plant species on Earth, trading nutrients and water for carbon that plants produce through photosynthesis. These networks are ecosystem engineers in the truest sense—they draw carbon into soils, regulate Earth's climate, and support much of the living world. Yet until now, scientists could only theorize about their distribution and sheer physical scale. The new global map, built in collaboration with the AMOLF Biophysics Institute in Amsterdam and data visualization designer Moritz Stefaner, makes the invisible visible at a resolution of one square kilometer across all terrestrial land.
To build their model, researchers assembled density data from more than 16,000 soil cores collected worldwide, then used machine learning to predict network distribution across unsampled ecosystems—from deserts to tundra to forests. They calibrated their predictions with robotic imaging of over 300,000 living fungal hyphae grown in the laboratory. The resulting estimate is staggering: these underground networks contain a total mass of approximately 300 megatons of carbon, equivalent to four to six times the mass of every human being alive today.
The fungal architecture is incomprehensibly intricate. Dr. Justin Stewart, lead author at SPUN, describes it with precision: there could be up to 10 meters of mycorrhizal network in just a teaspoon of soil. In healthy soils, these networks expand a plant's foraging area by up to 100 times while delivering more than 80 percent of the plant's phosphorus. Last year, Stewart and colleagues measured carbon flowing through these networks at speeds reaching 120 micrometers per second—which, at human scale, would feel like traveling at 400 kilometers per hour through a living transport system.
But the map also reveals alarming patterns. Mycorrhizal densities across croplands are predicted to be roughly half those in wild ecosystems, a sign that agricultural intensification is degrading these critical underground communities. This matters because every farm, forest, and garden depends on fungal networks to function. The researchers have made their underlying data available to governments and decision-makers, hoping that visibility will spur protection and monitoring.
"With the emergence of new technologies in high-resolution imaging, machine learning and robotics, we are starting to reveal what has long been hidden under our feet," said co-lead author Dr. Corentin Bisot of AMOLF. What was hidden is now mapped—a blueprint of Earth's living infrastructure that connects all plants and sustains all life above ground. The challenge ahead is ensuring these networks remain healthy as human activity reshapes the planet's soil.