Beneath our human shallows

We need a new imagination for the whole Earth, linking the power of the deep planet with the vitality of the surface

by James Dinneen  BIO

An enormous sinkhole appeared in Guatemala City during Storm Agatha in 2010. Courtesy the Government of Guatemala/Flickr

is a science and environmental journalist from Colorado based in New York City. His book about Earth’s deep interior is forthcoming.

Edited byRichard Fisher

When Soviet engineers began to drain the Aral Sea in the 1960s, they could hardly foresee the scale on which their handiwork would alter the planet. The goal was to irrigate large areas of what is now Uzbekistan and Kazakhstan to grow cotton, part of a utopian project stretching back to czarist Russia to civilise the ‘backward’ regions of central Asia. Achieving this meant diverting most of the two rivers that fed the Aral Sea, which was then the fourth largest lake in the world, larger than Lake Michigan. The engineers didn’t mean to empty it, but that was the outcome: the loss of input from the rivers, along with drought, caused nearly 90 per cent of its area to dry up over the next several decades. Today, abandoned fishing boats sit on the empty expanse as evidence of one of the 20th century’s largest environmental catastrophes.

The Aral Sea in 1989 (left) and 2014 (right). Courtesy Wikipedia

But the consequences of this event were not limited to the surface. The disappearance of around 1,000 cubic km of water provoked a rebound response all the way down in the upper mantle. Without that mass of water pressing down, the crust began to rise. In 2025, the geophysicist Teng Wang at Peking University and colleagues used satellites to measure the rate of uplift – known as isostatic adjustment or the ‘mattress effect’. They found an average rise across the former sea since 2016 of about 7 mm per year. Their models suggest that could occur only if viscous rocks in the upper mantle were ‘creeping’ into the space beneath the crust – as far as 190 km below the surface.

This is, as far as I’ve been able to determine, the deepest effect that a single human act has had on Earth. Our deliberate subterranean activities don’t come close. The deepest mine reaches no more than 4 km beneath the surface in South Africa. The deepest hole ever drilled, the Kola ‘Superdeep’ Borehole in northern Russia – another Russian engineering megaproject – punctures just 12 km down. Decades of scientific efforts to drill a ‘mohole’ into the mantle by boring into the thinnest parts of oceanic crust have been unsuccessful.

From that standpoint, the fact that a man-made environmental disaster altered the upper mantle is a shocking illustration of the scale of the planetary transformations that mark the Anthropocene – the age in which humans are supposedly the central geological force on Earth. It would also seem to suggest that human activity could be affecting Earth’s interior in other ways. What does the Anthropocene look like from below?

I’ve been thinking about this question of late because of a book I’m writing about the deep Earth, both the role it plays in making a habitable planet and how scientists have investigated its secrets. While human influence on Earth has certainly pushed deeper in the Anthropocene, what has become clear to me is that, from the planet’s perspective, we’re actually quite a shallow species. Our future scraping by up here on the surface depends on coming to terms with that.

Join more than 270,000 newsletter subscribers

Join more than 270,000 newsletter subscribers

Our content is 100 per cent free and you can unsubscribe anytime.

Our content is 100 per cent free and you can unsubscribe anytime.

For the most part, debates about the Anthropocene have focused more on when it started rather than where its influence extends. Did it begin at the dawn of agriculture? The Industrial Revolution? Or the mid-20th century, when nuclear weapons testing imprinted rocks worldwide? Ultimately, disagreement over whether this epochal change could be tied to a single discrete marker in the strata led to its rejection as an official new chapter in the geological record. But the term continues to be widely used as a catch-all for the planetary impacts the industrialised world now has on Earth, including those that extend increasingly far beneath the surface.

For instance, in a study from 2024, a group of geoscientists led by Grant Ferguson at the University of Saskatchewan estimated the volume of fluid moving through the subsurface due to global oil and gas production and mining, and found this human-caused flux now exceeds the total natural flow of groundwater deeper than 500 metres. This suggests that, as far as half a kilometre down, humans are, at the moment, the main event. The most significant consequence of pumping up all those ancient hydrocarbons is climate change – this is a shift of carbon from the lithosphere to the atmosphere far outpacing the largest super-eruptions in Earth’s history. There are also consequences within the subsurface itself. The movement of all that fluid has also induced earthquakes in some cases. The researchers suggested it may also have effects on the microbial ecosystems that thrive within the vast ‘deep biosphere’ that lives within the crust, although, like many things about this deep life, the nature of those impacts is unknown.

This isn’t just a picture of fossil fuel extraction, though. The researchers anticipated this deep fluid flux would see a substantial acceleration with a green transition away from fossil fuels, given the expansion of mining required........

© Aeon