Beneath our feet


Salomon Kroonenberg
Mythology and geology of the Underworld
304pp. Reaktion. £25.
978 1 78023 045 0

Published: 5 February 2014
The underground entrance to a volcano in the Kamchatka Peninsula, Russia The underground entrance to a volcano in the Kamchatka Peninsula, Russia Photograph: BUDKOV DENIS/CATERS NEWS

L ook upwards on a clear moonless night, and you behold a universe of stars, myriad beacons from both long ago and far away. Look down, and you see your feet and the ground on which they stand, nothing more. What lies within the Earth, beneath the rocks, soils and seas that bound our everyday experience? To classical commentators the answer was clear: the kingdom of Hades, subterranean home of the dead and, later, the damned. Science’s account is different, but in its own way equally fantastic. We live atop slowly roiling layers of crust, mantle and core whose heat-driven dynamics shape landscapes and geography, perhaps even life itself. In Why Hell Stinks of Sulfur, Salomon Kroonenberg chronicles humanity’s journey from one mode of explanation to the other.

Kroonenberg begins in Jerusalem, from which Jesus (according to the fourth century gospel of Nicodemus) descended into Hell. Combing through the Old City and nearby Ketef Hinnom, he searches for Jesus’s portal, but to no avail; candidate sites are both unconvincing and uninspiring. Disappointment similarly attends pilgrimages to Lake Averno, the “foul jaws of stinking Avernus” through which Aeneas entered the Underworld, and to western Greece, where the confluence of the Cocytus and Acheron rivers marks Odysseus’ gateway to Hell. Both sites actually exist – a few clicks suffice to locate them on Google Maps – but they prove to be placid waterways, better suited to weekend excursions than crossing the bar. As Arthurians who have trekked to Dozmary Pool can attest, the geography of myth metamorphoses readily into mythical geography. The pleasure of joining Kroonenberg in his odyssey lies not in any fleeting glimpse of Hell, but rather in the finely wrought explanations of Mediterranean geology sprinkled throughout the text. Caves provided antiquity’s surest route into the Underworld, underground rivers its subterranean highways, and volcanic hot springs the evidence that Hell was hot and, indeed, stank of sulphur. Kroonenberg lucidly explains the origins of caves and karst, calderas and carbonates, but neither science nor epic takes us more than a few tens of metres into the Earth.

Descriptions of Hell became more dramatically detailed with the Christian emphasis on punishment, and no account is more vivid than Dante’s. With Virgil as guide, Dante descends through nine circles of Hell, from the pleasant groves of Limbo, where Homer, Socrates and other honourable but unbaptized figures wait out eternity, to deeper levels with horrific torments. To us, Dante’s subterranean geography seems obviously moral and not literal, but this would not have been evident to medieval and Renaissance readers. Indeed, in 1587, the Florentine Accademia invited the young Galileo to evaluate competing reconstructions of Hell. His precise calculations of the Underworld’s dimensions show nascent science in support of theology; only later would physics and mineralogy provide an alternative narrative.

Dante’s subterranean geography seems obviously moral and not literal, but this would not have been evident to medieval and Renaissance readers

Different ways of knowing mingle, as well, in Georgius Agricola’s (Georg Bauer’s) magisterial De re metallica (1556), generally considered the foundational text of mining. Throughout, Agricola mixes strikingly modern commentary on how to dig shafts and extract ore with warnings about demons likely to be encountered in the process. Demons notwithstanding, mines extended human exploration into the Earth – up to about 800 m before the industrial age and now nearly 4,000 m in the gold mines of South Africa. At this depth, hot and mind-numbingly humid, miners labour to a persistent cadence of small creaks euphemistically said to be singing rocks, but actually pressure bursts that continually (and occasionally, catastrophically) deform shaft walls. Hell, indeed.

The deepest rocks observed in place by humans, then, lie some 6,367 kilometres from the centre of the Earth. How can we explore our planet’s greater volume? At this point, classical accounts fail us, but drilling helps a bit. Originally developed to extract petroleum from reservoirs up to a few kilometres deep, drilling for scientific purposes has recovered rock samples some twelve kilometres down. Fortunately, the Earth itself occasionally makes deeper materials available. For example, at plate tectonic boundaries, extraordinary features called ophiolites preserve slices of oceanic crust and upper mantle scraped off one plate on to another. Most famously observed in Cyprus, but spectacularly exposed, as well, in Oman and Newfoundland, ophiolites enable geologists to study rocks formed tens of kilometres below the Earth’s surface. Still deeper samples can be transported to the surface by magmas generated deep within the mantle. Diamonds crystallize only at pressures and temperatures found more than 150 km within the Earth, but they adorn rings and pendants because molten rocks have brought them to us. Indeed, tiny inclusions within diamonds provide further glimpses of our planet’s interior – flecks of mantle incorporated as the gemstones formed. For the rest, scientists rely on physics, using earthquake waves to generate a tomographic view of the deep Earth, much as CAT scans illuminate our anatomy.

The book requires patience on the part of the reader – Kroonenberg loves digression and only slowly reveals his narrative arc. But the rewards are substantial. Kroonenberg interleaves science, history and autobiography with a light touch, blending lively accounts of classical scholarship with superb descriptions of Earth’s interior and how geologists have come to know it. Virgil may no longer be available to accompany us through Hell, but Salomon Kroonenberg proves a witty and erudite guide for the twenty-first century.

Andrew H. Knoll is the author of Life on a Young Planet: The first three billion years of evolution on Earth, which appeared in 2003. He teaches Biology and Earth Science at Harvard University.

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