Sifting through
the sand of time
When
you're on the beach, you're stepping on ancient mountains, skeletons of marine
animals, even tiny diamonds. Sand provides a mineral treasure-trove, a record
of geology's earth-changing processes.
Sand:
as children we play on it and as adults we relax on it. It is something we
complain about when it gets our food and praise when it's moulded into castles.
But we don't often look at it. If we did, we would discover an account of a
geological past and a history of marine life that goes back thousands and in
some cases millions of years.
Sand
covers not just sea-shores, but also ocean beds, deserts and mountains. It is
one of the most common substances on earth. And it is a major element in
man-made items too – concrete is largely sand, while glass is made of little
else.
What
exactly is sand? Well, it is larger than fine dust and smaller than shingle. In
fact, according to the most generally accepted scheme of measurement, devised
by the Massachusetts Institute of Technology, grains qualify if their diameter
is greater than o.06 of a millimeter and less 0.6 of a millimeter.
Depending
on its age and origin, a particular sand can consists of tiny pebbles or porous
granules. Its grain may have the shape of stars or spirals, their edges jogged
or smooth. They have come from the erosion of rocks, or from the skeletons of
marine organisms which accumulate of the bottom of the oceans, or even from
volcanic eruptions.
Colour
is another clue to sand's origins. If it is dazzling white, its grains may be
derived from nearby coral outcrops, from crystalline quartz rock or from
gypsum, like the white sands of New Mexico. On Pacific island jet black sands
form from volcanic minerals. Other black beaches are magnetic. Some sand is
very recent indeed, as is the case on the island of Kamoama in Hawaii, where a
beach was created after a volcanic eruption in 1990. Molten lava spilled into
the sea and exploded in glassy droplets.
Usually,
the older the granules, the finer they are and the smoother the edges. The
fine, white beaches of northern Scotland, for instance, are recycled from
sandstone several hundred million years old. Perhaps they will be stone once
more, in another few hundred million.
Sand
is an irreplaceable industrial ingredient whose uses are legion: but it has one
vital function you might never even notice. Sand cushions our land from the
sea's impact, and geologist say it often does a better job of protecting our
shores than the most advanced coastal technology.
Answer
the questions below.
Choose NO MORE THAN THREE WORDS from the passage for each answer.
1.
What TWO materials made by
humans are mentioned in the passage?
2.
Which part of a grain of sand have scientists measured?
3.
What TWO factors determine the size and shape
of a piece of sand?
4.
Which event produced the beach on Kamoama Island?
5.
Where, according to the passage, can beaches made of very ancient sand be found?
6.
Who claims that sand can have a more efficient function than coastal
technology?
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