James Dinneen writes:

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.

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? [Continue reading…]