Indelible signs of human activity on Earth: kilometers and kilometers of holes
Human activity has so profoundly altered the face of the planet that geologists believe the era we are living in can be called the 'Anthropocene'. Among the most disfiguring and indelible operations, the digging of holes in the Earth's crust, kilometers deep.
It is estimated that humans have altered over half of the planet's surface.
These changes are easy to notice: mountains are excavated, forests are reduced, and an increasing number of living species are becoming extinct.
The changes are so dramatic for the planet that some geologists have named this phase of the Earth's geological timeline the 'Anthropocene'.
This concerns human activities on the surface. But what signs are we leaving in the depths of the subsurface?
It is believed that human activity beneath the surface is causing a continuous change of the Earth: a sprawling network of holes made for mining, energy, or exploratory activities provides further evidence that the Earth has entered the era of the Anthropocene.
Out of sight, out of mind
The distance between the surface of the planet and its center is about 6,373 kilometers. Animal life ceases to exist at about 2 kilometers below the surface, where some miners have discovered 'extremophile' worms in the gold mines of South Africa.
However, it is known that microbial life can survive at a depth of 2.7 kilometers. But, according to geologists, humans have managed to leave an indelible mark well beyond these depths.
When an animal dies, it leaves behind a skeletal trace, along with hundreds of fossil traces in the form of burrows. Most animals leave these traces just a few centimeters deep.
The boldest diggers are the Nile crocodiles, reaching depths of 12 meters. The roots of the African tree Boscia albitrunca, also known as the Shepherd's Tree, can reach 68 meters deep.
Humans have also managed to leave fossil traces of their presence in the subsoil of the planet, only these reach a depth of 12.3 kilometers, permanently altering the layers of rock.
"No other species has ever reached such depths in the Earth's crust, or made so many changes deep within the planet," the researchers write in the study published in the journal 'Anthropocene'.
Permanent changes
The first human forays into the subsurface occurred during the Bronze Age, when people began to dig shallow mines in search of flint and metals. The industrial revolution of the 1800s pushed humans to greater depths. However, many of the holes, such as wells for water, sewers, and subway lines, were relatively not very extensive, pushing to less than 100 meters deep.
Only from 1950, in the period some geologists call the "great acceleration," have humans begun to push beyond 100 meters.
The growing demand for resources has led to the digging of more mines to collect coal and other minerals. In most cases, extraction extends only a few hundred meters deep, but the gold mines in South Africa push nearly 5 kilometers beneath the surface.
In recent decades, more and more wells have appeared. Some are drilled to obtain geothermal energy, others are used to extract natural materials from the Earth, such as hydrocarbons, gas, and minerals. The wells are then filled with other materials, including mud, cement, or solid waste.
If all the oil wells were stacked one on top of the other, they would reach a length of 50,000 kilometers, roughly the distance between Earth and Mars. For every human being, there are about 7 meters of drilling.
The extracted oil is often replaced with water that seeps from nearby rocks or with carbon dioxide, which is pumped in during a process called 'Carbon Capture and Storage'.
The most severe damage is caused by underground nuclear tests. Test sites show the breaking and melting of surrounding rocks, with severe contamination of groundwater. The underground caverns are then used for the storage of radioactive waste from the tests.
These human-induced changes beneath the surface will remain there, shielded from natural erosion, for a very, very long time.
