Reading UNIT 2
Sifting
through
the Sands
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 ft gets in our food,
and praise when ft'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 materials 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 0.06 of a millimetre and less than
0.6 of a millimetre.
Depending on its age and origin, a particular sand can
consist of tiny pebbles or porous granules. Its grains may
have the shape of stars or spirals, their edges lagged or
smooth. They have come from the erosion of rocks, or from
the skeletons of marine organisms, which accumulate on the
bottom of the oceans, or even from volcanic eruptions.
Colour is another clue to sand's origins. If it is a dazzling
white, its grains may be derived from nearby coral outcrops,
from crystalline quartz rocks or from gypsum, like the white
sands of New Mexico. On Pacific Islands 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, Motten lava spilled into the sea and
exploded in glassy droplets.
Usually, the older the granules, the finer they are and the
smoother their 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 ft has one vital function you might never even
notice. Sand cushions our land from the sea's impact, and
geologists say it often does a better job of protecting our
shores than the most advanced coastal technology.
Discuss your answers to the six questions as a class. What sort of answers would
lose marks?
What other factual information could be tested in this passage?