The world in a grain of sand

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Sand: A Journey through Science and the Imagination

Oxford University Press: 2009. 352 pp. £18.99 9780199563180 | ISBN: 978-0-1995-6318-0
Green desert glass from Libya was carved into a scarab beetle for Tutankhamun's necklace — but how did the silica glass form? Credit: PHOTO SCALA, FLORENCE/EGYPTIAN MUS., CAIRO

On an island off the southwestern coast of Turkey, called Sedir Adasi, lies a stunning stretch of white sand known as Cleopatra's Beach. According to legend, Cleopatra's lover Mark Antony made the beach for her as a lavish gift by shipping bargeloads of sand from Egypt to the island some 2,000 years ago. There may be a grain of truth in this story, writes Michael Welland in Sand — the “exotic creamy white oolith” granules occur nowhere else on the island but match those on Egyptian coastal beaches west of Alexandria.

A modern mystery of sand is the origin of the silica used in making silicon for the electronics industry. After much research, Welland drew a blank. The handful of technology companies who dominate this crucial market would not disclose the source of their raw material; all the author could deduce was that silicon chips are made from “sand that has already been ultrapurified by nature: quartzite”.

A popular book by a long-time professional geologist could easily have been worthy but dry. Yet Sand is serious and entertaining; it is the work of someone who has been in love with the stuff since he built sandcastles as a child. Nothing like it has been published before, even by the larger-than-life pioneer of sand studies, Ralph Bagnold, who serves as Welland's inspiration.

Bagnold was a British army officer who saw the Sphinx excavated in the 1920s from tonnes of preservative sand laid down over millennia. He became a desert explorer in Egypt and a formidable adversary behind enemy lines in the Second World War. He was also a scientist, and built a wind tunnel at Imperial College London to investigate the behaviour of sand grains under controlled conditions. In 1941 he published The Physics of Blown Sand and Desert Dunes, a classic study (see Nature 457, 1084–1085; 2009) that was later used by NASA to plan how its rovers should deal with Martian sand.

But Welland stretches beyond Bagnold and his deserts. Sand begins on the small scale, with the counter-intuitive physics of granular behaviour. Strangely, dry sand behaves like a liquid, whereas damp sand is more like a solid, provided that it is not too wet. Welland explains the stability and collapse of sand piles, and the forensic study of sand to solve murders. This leads to a discussion of the weird and wonderful microscopic life forms — such as rotifers, tardigrades, gastrotrichs, turbellarians and others — that have evolved to flourish in the spaces between shifting, abrasive sand grains. Such an environment may become the last refuge for life in the event of catastrophic climate change. Welland then addresses sand on a progressively larger scale: along the course of meandering rivers, in the formation of beaches, in deserts and mid-ocean sandbanks, in the formation of Old Red Sandstone rocks found extensively from the Arctic to the Gulf of Mexico and, finally, in sand found beyond Earth.

Welland asks how sand grains have helped humans to conceive the Universe and the infinite. He begins with Archimedes who, in the third century BC, calculated that 1063 grains of sand would fill the Universe to the outermost sphere of the fixed stars. The author also discusses, and attractively illustrates, how sand has been used artistically in many cultures — from sand painting by Australian aboriginal communities and the North American Navajo, to Zen sand gardens in Japan and the sand sculptures created by digital methods at the Media Lab at the Massachusetts Institute of Technology in Cambridge. One fascinating photograph shows the 'Earthquake Rose', the pattern made by a desktop toy, a sand-tracing pendulum, during a strong earthquake in Washington state in 2001.

A personal epilogue provides the reader with a genuine mystery. In 1922, the discovery of Tutankhamun's tomb in Egypt yielded a famous necklace with a scarab beetle carved from a glowing, yellow-green, gem-like material, which its discoverer Howard Carter did not recognize. In the 1990s, the material was shown to be a unique silica glass, 28 million years old and 98% pure, from a particular part of the Libyan desert.

Welland travels to this desolate spot and cherishes the glassy samples he finds glittering on the dunes. But, he muses, what could have produced heat that was intense enough to fuse silica? A strike from a meteorite or lightning can be ruled out because of the lack of visible impact craters or hollow fulgurite tubes, respectively. He speculates that the cause might have been an air burst from the impact of an asteroid with the atmosphere, similar to that at Tunguska in Siberia, Russia, in 1908.

With irresistible ideas such as this, Welland provides an appealing blend of science and the imagination, worthy of the famous vision of the poet William Blake: “To see a world in a grain of sand”.

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Robinson, A. The world in a grain of sand. Nature 460, 798–799 (2009) doi:10.1038/460798a

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