According to New Study, Over Half of Life on Earth is Found in the Soil

There are several million different species of plants, animals, insects, bacteria, and fungi on Earth – so many that scientists are still making daily discoveries about new forms of life on our planet. But Earth’s biodiversity goes far beyond what’s visible on the surface. Beneath our feet, a hidden world of life makes up even more than what we can see above the ground. According to a recent study, over half of life on Earth lives underground, making the soil the most biodiverse habitat on our planet. 

The gathering of life beneath the surface

While scientists have long been aware of the richness of life within soil, this new finding is nearly twice the amount that researchers predicted back in 2006, which claimed that 25% of all life was found dwelling in the ground. Based on the new figures, soil is likely home to about 59% of all life, from simple microbes to complex mammal species. The researchers of the study estimate that these numbers could be even higher, considering how understudied soil ecosystems are in scientific literature. The estimated error range is approximately 15%, more or less of the average.

“What actually surprised me the most was the sheer challenge of this undertaking, and how much variation there is to our estimates for many large groups, particularly bacteria and viruses, the two most diverse forms of life on Earth,” noted the lead researcher of the study, ecologist Dr. Mark Anthony. “Keeping that in mind, our estimate is really a first attempt to organise existing global richness albeit with quite a large error to many of the estimates. While true diversity lies somewhere within this range, our effort is the first realistic estimate of global diversity in soil, and we need it to advocate for soil life in the face of the biodiversity and climate crises,” he adds.

According to the research article published in the Proceedings of the National Academy of Sciences (PNAS), Enchytraeidae, small worms that break up the soil, make up the highest percentage of species in the ground, with around 98.6%. Additionally, 85.5% of plants and 84.2% of Isoptera (termite) species can be found in soil. 

An estimated 2 million different species of anthropods reside in the soil, which is around 30% of the total known anthropod species. These include invertebrates like insects, arachnids, and crustaceans. Mammals, such as moles and shrews, are the least found group within soil, at only 3%. That being said, most organisms that inhabit the soil are microscopic organisms, like the 430 million species of bacteria, which make up 50% of all bacteria. Or the 5.6 million species of fungi constituting around 90% of all fungi (1).

Beyond these figures, the millions of species that make up the biodiverse soil ecosystems interact with each other and play a pivotal role in soil health, which impacts life above the ground as well.

The importance of soil ecosystems

Soil is often overlooked as simply the dirt that we walk upon, but within the complex soil ecosystems are several processes that heavily impact all life on earth – whether on land, air, or water. Healthy soil often directly influences the health of aquatic and terrestrial ecosystems, and we rely on it to guarantee us nutritional food and combat climate change. Some of the main features of healthy soil include:

Facilitation of sustainable agriculture

Healthy soil is a significant aspect of successful agriculture. Nutrients from soil move into the plants and animals we eat. Healthier soil creates the most abundant, nutrient-dense crops. Unfortunately, as the health of soils has significantly decreased over time, so have the nutrients that our food absorbs. The decrease in nutrient-dense food serves as a threat to public health, as several people, primarily in low-income populations, can suffer from deficiencies.

Production of important antibiotics

The microorganisms in soil have evolved to create antibiotics that hinder their neighboring organisms to promote their own growth. Most of the antibiotics that we currently use have been found within the soil. For instance, penicillin, the world’s very first antibiotic, was derived from a soil fungus called Penicillium. However, the widespread use of penicillin and other antibiotics has led to evolving bacteria that are resistant to these drugs. Researchers hope that by studying soil bacteria, they can identify methods of reducing gene exchange amongst harmful bacteria, which could help slow the transmission of drug-resistant superbugs

Carbon sequestration

Over 70% of the Earth’s carbon pool is stored in the soil. Trees and mycorrhizal fungi work together, drawing carbon into the soil and stabilizing it in the ground. Some fungi are capable of creating exudates made from absorbed carbon and nitrogen. These exudates are consumed by microbes which immobilize them into a more stable form of carbon, preventing it from being further broken down. Digging, tilling, and plowing soil can expose microbes to oxygen, causing them to break down organic matter more rapidly and release stored carbon into the atmosphere.

Improving water quality and preventing erosion

Healthy soil filled with diverse biological activity contains a complex system of air and water pores. These pores help prevent erosion, especially if the soil is protected by plants and their root systems that hold everything in place. The pores in healthy soil also allow water in and help store it. Almost half of all drinking water worldwide comes from stored groundwater. As water moves through soil, it also becomes cleaned out and filtered from any chemical and biological pollutants. The soil holds onto these pollutants instead of releasing them into the groundwater, and the organisms in soil can help break them down into less hazardous substances. Hea

Protecting the earth’s soils through conservation and research

A UN-backed study called the Global Land Outlook found that over a third of our planet’s land is significantly degraded, and fertile soil is being lost at a rate of 24 billion tonnes a year, just from farming alone. Along with climate change, pollution, and deforestation, the numbers are even higher. 

Over the past two decades, the amount of irrigated land has doubled, and agricultural production has tripled. Unsustainable farming practices such as agrochemicals, monocropping, excessive tillage, lack of crop rotations, and livestock overgrazing have stripped the land of fertility, leaving it severely unhealthy and destroying the abundance of organisms within it. Over time, this damaged land is simply abandoned, and new plots of soil are used and abused until they are stripped of their nutrients as well. 

For decades, soil health had been completely ignored, leading to its current state. The majority of nature conservation efforts focus primarily on the destruction of oceans and terrestrial organisms, neglecting the status of unseen soil organisms. But thanks to growing research and land preservation efforts, many scientists and conservationists are searching for ways to protect and restore the Earth’s fertile soil. The researchers of the soil biodiversity study hope that their findings influence more individuals to advocate for soils amid the biodiversity crisis. 

“Like ‘canaries in the coalmine,’ when soil organisms begin to disappear, ecosystems will soon start to underperform, potentially hindering their vital functions for humankind,” wrote a group of 29 researchers led by soil ecologist Carlos António Guerra urging policymakers in a policy form (2). “If we do not protect soils for the next generations, future above-ground biodiversity and food production cannot be guaranteed.” 

References

1. Anthony, Mark, Sophia Bender, and Marcel. 2023. “Enumerating Soil Biodiversity.” Proceedings of the National Academy of Sciences of the United States of America 120 (33). https://doi.org/10.1073/pnas.2304663120.
2. Guerra, Carlos A., Richard D. Bardgett, Lucrezia Caon, Thomas W. Crowther, Manuel Delgado-Baquerizo, Luca Montanarella, Laetitia M. Navarro, et al. 2021. “Tracking, Targeting, and Conserving Soil Biodiversity.” Science 371 (6526): 239–41. https://doi.org/10.1126/science.abd7926.