Soils on display inside the Museum of Edible Earth's temporary exhibition at Somerset House in London. David Parry/PA Media Assignments, CC BY-SAEditor’s note: The UK’s Food Standards Authority and Health Security Agency both advise against eating clay, soil or earth. Links to their guidance are included in this article.When I ask people if they have ever eaten soil before, they tend to give me a strange look. But geophagy – the deliberate ingestion of any kind of soil – is a practice that archaeological evidence from Kalambo Falls in Zambia suggests has been part of human history for at least 2 million years.British archaeologist John Desmond Clark reported that Homo habilis, a species of human who lived between 2.2 and 1.6 million years ago, was digging into the earth to mine clays from below the topsoil. This led to the inference that the oldest evidence of geophagy by humans was at that prehistoric site on the border of Zambia and Tanzania.More recently, anecdotal evidence suggests a prisoner condemned to death in 16th-century Hohenlohe (now part of Germany) was allowed a last request of consuming a small clay tablet after receiving his supposedly lethal dose of mercury. The tablet was reputedly a piece of terra sigillata – clay traditionally mined from the Greek island of Lemnos. To the amazement of the court, the convict survived the mercury poisoning and was merely banished instead.Geophagy is still practised widely around the globe, including by some women experiencing food cravings during pregnancy. But it should not be confused with the eating disorder pica.In my research on geophagy practices in the UK, clays appear to be the most popular types of soil consumed. But these are only a sliver of the many types of soil people are known to eat.In Amsterdam’s Museum of Edible Earth, researcher and artist masharu has brought together more than 600 soils used in geophagy. These include melt-in-the-mouth pemba from Surinam and montmorillonite green clay from France, which is claimed to be an anti-ageing treatment.The museum is now in the UK for the first time. Adult visitors to Somerset House in London are being invited to sample a “tasting menu” of its soils, and even contribute their own tasting notes. Map of the Museum of Edible Earth soil samples. Graphic design by Luuk van Veen with guidance of Olga Ganzha and masharu, CC BY-SA The symbolism of soilFor many people, eating soil carries deep symbolic meaning. Soil is a common theme in genesis stories that describe how a people originated, including Adam in the Bible’s Old Testament.Among the Luo people in Kenya, women who practice geophagy during pregnancy prefer eating red clays due to the links between soil, fertility and blood. These clays are understood to replenish the blood lost during pregnancy to the unborn foetus, which is referred to as remo ma ichweyogo nyathi (the blood you form the child of).In the 20th century, eating soil was sometimes used to determine guilt in Java. If a crime was committed with no witnesses and the cross-examination failed, suspects would ingest a small amount of soil from their ancestors’ graves and call upon them as witnesses to their innocence. If one of the suspects grew ill or died over the next few months, they would be found guilty.Today, thinly sliced clay from Java is still eaten as a snack known as ampo.Soil’s growing appealThe benefits and risks of eating soil have been highlighted amid recent social media interest in geophagy, such as the trend for filming soil taste tests on TikTok. A collaboration between researchers at the universities of Glasgow, Strathclyde and Crete suggests clays from Lemnos may have wider health benefits, such as preventing the progression of inflammatory diseases (although, so far, only shown in mice).Bentonite, which is also used in cosmetic face masks, was mentioned as a favourite edible clay by some customers of a London health-food shop I spoke to.One reason clays such as bentonite appear to be a popular choice is that they can host Streptomyces, a genus of bacteria that, alongside being a useful source of antibiotics, produce geosmin. This chemical emits the pleasant smell associated with dry earth after rainfall – and also contributes to a pleasantly “earthy” taste. Video: NewsNation. But any kind of soil should always be consumed with caution. In 2013, Public Health England identified calabash chalk as a particular risk for pregnant women. Its warning was triggered by widespread consumption of this chalk within some Asian and African communities in London, as a nutritional supplement or morning sickness antidote, and the potential threat posed by lead present in some of these soils.The UK Food Standards Authority has also warned about the presence of lead and other toxic chemicals in commercially available clays.Some soils may contain hidden dangers such as heavy metals pollutants, parasitic worms and cancer-causing moulds. Additionally, faecal contamination of soils may introduce bacteria such as E coli, which can cause food poisoning. While these health risks do not apply to all soils, and some of these concerns can be addressed through the way clays are processed, it is advised that anyone interested in practising geophagy should seek careful guidance first.The exhibition of edible soils by masharu, on show in London until April 26, seeks to challenge the stigma and negative perceptions around eating clay by focusing on the often-overlooked sensations of soil. From environmental science to health research, soil is no longer being treated like dirt.Zander Simpson receives funding for his research from the Economic and Social Research Council in the form of a PhD Studentship.