VOA标准英语2010-Sand Tells a 'Never-Ending Story'

Grab a handful and you'll see "a world in a grain of sand"

Adam Philips | New York 15 April 2010

Close up, sand grain can appear jewel-like. Indeed, many gems 1, such as diamonds and sapphires 2, are made from ancient sands.

Related Links

"Sand: The Never-Ending Story"

Michael Wellands's Blog

American Museum of Natural History

John Burroughs Association

Whether at the desert, on the beach or piled up at a construction site, sand is one of the most  common, useful and wondrous 3 materials on earth.

But what is sand? Where does it come from? How is it formed and how does it behave?

Never-Ending Story

Those are questions that prompted British geologist 4 Michael Welland to write his book-length ode to the stuff, "Sand: the Never-Ending Story."

"Sand is an apparently 5 mundane 6 everyday material," says Welland, "and yet the journeys an individual sand grain can take you on, both physically 7 and imaginatively, I found extraordinary." 

Geologist Michael Welland collects sand samples in central California.

Geologist and physicists 8 long ago decided 9 that what makes sand sand is the size of the individual granular bits, not what they are made of. Welland notes that sand grains differ from other granular materials, both in the way they pile, and in how they behave. 

"When they're flowing in the air or flowing in water, for example, they behave very differently from everything that is smaller — that's silt 10 and mud — and everything that is bigger — that's gravel 11 and pebbles 12 and cobbles and boulders 13."

Welland's book about sand earned him the prestigious 14 John Burroughs Medal for natural history writing, which was presented earlier this month at New York's American Museum of Natural History. He was right at home in that august locale; sand is an important element in the beautiful old building's sparkling pink granite 15 fa?ade. 

'Sand: the Never-Ending Story' has garnered 16 geologist Michael Welland the 2010 John Burroughs Medal for natural history writing.

A Sand Grain Is Born

"Well, what's sparkling are quartz 17 grains. In a few million years, the granite of the Natural History Museum, exposed to the elements of New York, will begin to rot and disintegrate," says Welland. As the most frail 18 minerals dissolve, "the quartz, which is as tough as old boots, will eventually just drop out as a sand grain."  

Some of those quartz sand grains will be washed away by rainwater into nearby rivers where they will make their way down to the shoreline, and the sea or get blown to the desert. In the desert, sand grains are usually buffeted 19 and shaped by the wind, which tends to make them smooth and rounded.

"The sand grains bang into each other," says Welland, "and that force tends to knock the rough edges off a grain." Desert sands are often frosted like sand blasted glass.

The beauty and variety of sand is visible in this array from South Africa, arranged by the artist Loes Modderman.

"But," says Welland "if you go to the beach where the water buffers 20 the impact between grains, it takes millions and millions of years to knock their rough edges off."   

In yet another kind of transformation 21, grains of coastal 22 sand can get squeezed together by the weight of overlying sediments 23 and become rock themselves, which is how sandstone gets formed.

Welland explains that those sand stones can then be churned back up to the earth's surface by the movement of the earth's plates and then those sandstones themselves will rot.

"And so, the sand grain starts off on a second life journey. Many of the grains we see on the beach will have been through two, three, four, five of those cycles over hundreds of millions of years."   

 British geologist Michael Welland says sand has many uses in the modern world.

Sand families

Sand grains tend to group together in "families" according to mineral type, density 24, shape, weight and other factors. The relative proportion of these groupings in any one area of beach is unique.

Sand can even be used as forensic 25 evidence in criminal investigations 26. For example, if the specific array of minerals in the sand found in a suspect's shoe match the stretch of beach where a murder victim is found, the owner of that shoe might be wise to call a lawyer. 

Welland says sand has so many other uses that the modern world would be unrecognizable without it.

"We wouldn't have any glass or concrete, or the mobile phones or computers we have now — or they would have to work in completely different ways. Much of the world's jewelry 27 would disappear. Sapphires and diamonds, for example, come from ancient deposits of sand [where] rivers have winnowed 28 the minerals away."

"A World in a Grain of Sand…"

In his book "Sand: the Never-Ending Story," Michael Welland says that sand's beauty and diversity are every bit as compelling as its science.

He advises skeptics to bring a magnifying glass next time they go to the beach, grab a handful, and take a close look.

He confidently predicts that, like the mystic British poet William Blake, you'll see "a world in a grain of sand."