[Reading Science] Most Earth Organisms Live in the □□

Swiss Research Team Publishes Study on 7th
Soil Ecosystem Accounts for 59% of All Organisms
"Very Valuable but Unappreciated"

Research has revealed that most living organisms on Earth reside underground.

A research team from the University of Zurich in Switzerland published a paper on the 7th in the academic journal 'PNAS (Proceedings of the National Academy of Sciences)' issued by the U.S. National Academy of Sciences. The team found that about 59% of living species live in the soil, confirming that soil is the single most biologically diverse habitat on Earth. This figure is more than double the approximately 25% estimated in another study published in 2006. The researchers expect that as studies on soil ecosystems advance, more organisms will be identified, potentially increasing this proportion. By category, 90% of fungi, 85% of plants, and over 50% of bacteria live in the soil. However, only 3% of mammals live underground, showing the least association.

Soil forms the uppermost layer of the Earth's surface and is a mixture of water, gases, minerals, and organic matter. Although more than 95% of food grows in soil, humans often exclude it from conservation efforts due to a lack of understanding. However, a single teaspoon of healthy soil contains a billion bacteria and one kilometer of fungal filaments, making it a treasure trove of life.

The research team estimated that there are a total of 10 billion species on Earth and then used theoretical calculations and data analysis to determine the proportion of species found in soil. They identified organisms that live in the soil or on the ground, or spend part of their life cycle underground. Other habitats outside the soil were classified as marine, freshwater, seabed, air, buildings, and host organisms.

The sampling error was set at an average of about 15%, which is relatively large. Therefore, the proportion of soil organisms could range from a maximum of 74% to a minimum of 44%. In particular, the margin of error for bacteria was set wider, estimating that they could account for between 22% and 89% of all soil species. This reflects the fact that humans still do not have a deep understanding of bacteria and viruses, which constitute the largest proportion of species on Earth.

Mark Anthony, an ecology researcher at the Swiss Federal Institute for Forest, Snow and Landscape Research who participated in the study, explained, "Before this research, it was not confirmed which habitat on Earth harbors the most living organisms. Soil organisms have a significant impact on Earth's balance. Their diversity is very important because it greatly affects climate change, global food security, and human health."