The human species has not only transformed the Earth’s surface: beneath our feet there is a network of boreholes, wells, tunnels and mine galleries whose accumulated length reaches astronomical figures. According to an article published by Muy Interesante, based on the work of geologist Jan Zalasiewicz and other Anthropocene researchers, humans have drilled the subsoil over an extent equivalent to tens of millions of kilometres — a distance that directly competes with the total length of the roads of the entire planet.
To put it in perspective, the circumference of the Earth is about 40,000 kilometres. This means that all human drilling added together could make thousands of complete laps around the globe. And yet, this colossal underground work goes practically unnoticed by most people.
The most emblematic example of this obsession with reaching the depths is the Kola superdeep borehole, on the Kola Peninsula (Russia). Drilled between 1970 and 1990, it reached a depth of 12,262 metres with a diameter of barely 23 centimetres, becoming the deepest hole ever dug by humans. The project encountered unexpected temperatures of up to 180 degrees Celsius that forced the drilling to stop, but it left a legacy of discoveries about the composition of the Earth’s crust.
At the other end of the spectrum are open-pit mines, such as the Bingham Canyon mine in Utah (USA), visible from space, several kilometres wide and more than a kilometre deep. And between both extremes, millions of oil, geothermal and water wells and geological surveys make up a true global underground infrastructure.
Geologists consider that this network of boreholes will be one of the most durable physical markers of the Anthropocene, the geological epoch marked by human activity. While buildings, roads and monuments will disappear over the millennia, many of these underground cavities could remain recognizable over geological timescales. As science journalist David Farrier points out in his book Footprints: In Search of Future Fossils, these boreholes represent a silent and deep legacy of our species, etched into the planet’s physical history for future geologists — whether human or otherwise.
