31 British Columbia

British Columbia is the third largest Canadian provinces, both in area
and population. It is nearly 1.5 times as large as Texas, and extends
800 miles(1,280km) north from the United States border. It includes
Canada’s entire west coast and the islands just off the coast.

Most of British Columbia is mountainous, with long rugged ranges running
north and south. Even the coastal islands are the remains of a mountain
range that existed thousands of years ago. During the last Ice Age, this
range was scoured by glaciers until most of it was beneath the sea. Its
peaks now show as islands scattered along the coast.

The southwestern coastal region has a humid mild marine climate. Sea
winds that blow inland from the west are warmed by a current of warm
water that flows through the Pacific Ocean. As a result, winter
temperatures average above freezing and summers are mild. These warm
western winds also carry moisture from the ocean.

Inland from the coast, the winds from the Pacific meet the mountain
barriers of the coastal ranges and the Rocky Mountains. As they rise to
cross the mountains, the winds are cooled, and their moisture begins to
fall as rain. On some of the western slopes almost 200 inches (500cm) of
rain fall each year.

More than half of British Columbia is heavily forested. On mountain
slopes that receive plentiful rainfall, huge Douglas firs rise in
towering columns. These forest giants often grow to be as much as 300
feet(90m) tall, with diameters up to 10 feet(3m). More lumber is
produced from these trees than from any other kind of tree in North
America. Hemlock, red cedar, and balsam fir are among the other trees
found in British Columbia.

32 Botany

Botany, the study of plants, occupies a peculiar position in the history
of human knowledge. For many thousands of years it was the one field of
awareness about which humans had anything more than the vaguest of
insights. It is impossible to know today just what our Stone Age
ancestors knew about plants, but form what we can observe of pre-
industrial societies that still exist a detailed learning of plants and
their properties must be extremely ancient. This is logical. Plants are
the basis of the food pyramid for all living things even for other
plants. They have always been enormously important to the welfare of
people not only for food, but also for clothing, weapons, tools, dyes,
medicines, shelter, and a great many other purposes. Tribes living today
in the jungles of the Amazon recognize literally hundreds of plants and
know many properties of each. To them, botany, as such, has no name and
is probably not even recognized as a special branch of “ knowledge” at
all.

Unfortunately, the more industrialized we become the farther away we
move from direct contact with plants, and the less distinct our
knowledge of botany grows. Yet everyone comes unconsciously on an
amazing amount of botanical knowledge, and few people will fail to
recognize a rose, an apple, or an orchid. When our Neolithic ancestors,
living in the Middle East about 10,000 years ago, discovered that
certain grasses could be harvested and their seeds planted for richer
yields the next season the first great step in a new association of
plants and humans was taken. Grains were discovered and from them flowed
the marvel of agriculture: cultivated crops. From then on, humans would
increasingly take their living from the controlled production of a few
plants, rather than getting a little here and a little there from many
varieties that grew wild- and the accumulated knowledge of tens of
thousands of years of experience and intimacy with plants in the wild
would begin to fade away.

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33 Plankton浮游生物. / 'plжηktэn; `plжηktэn/

Scattered through the seas of the world are billions of tons of small
plants and animals called plankton. Most of these plants and animals are
too small for the human eye to see. They drift about lazily with the
currents, providing a basic food for many larger animals.

Plankton has been described as the equivalent of the grasses that grow
on the dry land continents, and the comparison is an appropriate one. In
potential food value, however, plankton far outweighs that of the land
grasses. One scientist has estimated that while grasses of the world
produce about 49 billion tons of valuable carbohydrates each year, the
sea’s plankton generates more than twice as much.

Despite its enormous food potential, little effect was made until
recently to farm plankton as we farm grasses on land. Now marine
scientists have at last begun to study this possibility, especially as
the sea’s resources loom even more important as a means of feeding an
expanding world population.

No one yet has seriously suggested that “ plankton-burgers” may soon
become popular around the world. As a possible farmed supplementary food
source, however, plankton is gaining considerable interest among marine
scientists.

One type of plankton that seems to have great harvest possibilities is a
tiny shrimp-like creature called krill. Growing to two or three inches
long, krill provides the major food for the great blue whale, the
largest animal to ever inhabit the Earth. Realizing that this whale may
grow to 100 feet and weigh 150 tons at maturity, it is not surprising
that each one devours more than one ton of krill daily.

34 Raising Oysters

In the oysters were raised in much the same way as dirt farmers raised
tomatoes- by transplanting them. First, farmers selected the oyster bed,
cleared the bottom of old shells and other debris, then scattered clean
shells about. Next, they ”planted” fertilized oyster eggs, which
within two or three weeks hatched into larvae. The larvae drifted until
they attached themselves to the clean shells on the bottom. There they
remained and in time grew into baby oysters called seed or spat. The
spat grew larger by drawing in seawater from which they derived
microscopic particles of food. Before long, farmers gathered the baby
oysters, transplanted them once more into another body of water to
fatten them up.

Until recently the supply of wild oysters and those crudely farmed were
more than enough to satisfy people’s needs. But today the delectable
seafood is no longer available in abundance. The problem has become so
serious that some oyster beds have vanished entirely.

Fortunately, as far back as the early 1900’s marine biologists realized
that if new measures were not taken, oysters would become extinct or at
best a luxury food. So they set up well-equipped hatcheries and went to
work. But they did not have the proper equipment or the skill to handle
the eggs. They did not know when, what, and how to feed the larvae. And
they knew little about the predators that attack and eat baby oysters by
the millions. They failed, but they doggedly kept at it. Finally, in the
1940’s a significant breakthrough was made.

The marine biologists discovered that by raising the temperature of the
water, they could induce oysters to spawn not only in the summer but
also in the fall, winter, and spring. Later they developed a technique
for feeding the larvae and rearing them to spat. Going still further,
they succeeded in breeding new strains that were resistant to diseases,
grew faster and larger, and flourished in water of different salinities
and temperatures. In addition, the cultivated oysters tasted better!

35.Oil Refining

An important new industry, oil refining, grew after the Civil war. Crude
oil, or petroleum - a dark, thick ooze from the earth - had been known
for hundreds of years, but little use had ever been made of it. In the
1850’s Samuel M. Kier, a manufacturer in western Pennsylvania, began
collecting the oil from local seepages and refining it into kerosene.
Refining, like smelting, is a process of removing impurities from a raw
material.

Kerosene was used to light lamps. It was a cheap substitute for whale
oil, which was becoming harder to get. Soon there was a large demand
for kerosene. People began to search for new supplies of petroleum.

The first oil well was drilled by E.L. Drake, a retired railroad
conductor. In 1859 he began drilling in Titusville, Pennsylvania. The
whole venture seemed so impractical and foolish that onlookers called it
“ Drake’s Folly”. But when he had drilled down about 70 feet(21
meters), Drake struck oil. His well began to yield 20 barrels of crude
oil a day.

News of Drake’s success brought oil prospectors to the scene. By the
early 1860’s these wildcatters were drilling for “ black gold” all
over western Pennsylvania. The boom rivaled the California gold rush of
1848 in its excitement and Wild West atmosphere. And it brought far more
wealth to the prospectors than any gold rush.

Crude oil could be refined into many products. For some years kerosene
continued to be the principal one. It was sold in grocery stores and
door-to-door. In the 1880’s refiners learned how to make other
petroleum products such as waxes and lubricating oils. Petroleum was not
then used to make gasoline or heating oil.

36.Plate Tectonics and Sea-floor Spreading

The theory of plate tectonics describes the motions of the lithosphere,
the comparatively rigid outer layer of the Earth that includes all the
crust and part of the underlying mantle. The lithosphere(n.[地]岩石圈)is
divided into a few dozen plates of various sizes and shapes, in general
the plates are in motion with respect to one another. A mid-ocean ridge
is a boundary between plates where new lithospheric material is injected
from below. As the plates diverge from a mid-ocean ridge they slide on a
more yielding layer at the base of the lithosphere.

Since the size of the Earth is essentially constant, new lithosphere can
be created at the mid-ocean ridges only if an equal amount of
lithospheric material is consumed elsewhere. The site of this
destruction is another kind of plate boundary: a subduction zone. There
one plate dives under the edge of another and is reincorporated into the
mantle. Both kinds of plate boundary are associated with fault systems,
earthquakes and volcanism, but the kinds of geologic activity observed
at the two boundaries are quite different.

The idea of sea-floor spreading actually preceded the theory of plate
tectonics. In its original version, in the early 1960’s, it described
the creation and destruction of the ocean floor, but it did not specify
rigid lithospheric plates. The hypothesis was substantiated soon
afterward by the discovery that periodic reversals of the Earth’s
magnetic field are recorded in the oceanic crust. As magma rises under
the mid-ocean ridge, ferromagnetic minerals in the magma become
magnetized in the direction of the magma become magnetized in the
direction of the geomagnetic field. When the magma cools and solidifies,
the direction and the polarity of the field are preserved in the
magnetized volcanic rock. Reversals of the field give rise to a series
of magnetic stripes running parallel to the axis of the rift. The
oceanic crust thus serves as a magnetic tape recording of the history of
the geomagnetic field that can be dated independently; the width of the
stripes indicates the rate of the sea-floor spreading.

37 Icebergs

Icebergs are among nature’s most spectacular creations, and yet most
people have never seen one. A vague air of mystery envelops them. They
come into being ----- somewhere ------in faraway, frigid waters, amid
thunderous noise and splashing turbulence, which in most cases no one
hears or sees. They exist only a short time and then slowly waste away
just as unnoticed.

Objects of sheerest beauty they have been called. Appearing in an
endless variety of shapes, they may be dazzlingly white, or they may be
glassy blue, green or purple, tinted faintly of in darker hues. They are
graceful, stately, inspiring ----- in calm, sunlight seas.

But they are also called frightening and dangerous, and that they are ---
- in the night, in the fog, and in storms. Even in clear weather one is
wise to stay a safe distance away from them. Most of their bulk is
hidden below the water, so their underwater parts may extend out far
beyond the visible top. Also, they may roll over unexpectedly, churning
the waters around them.

Icebergs are parts of glaciers that break off, drift into the water,
float about awhile, and finally melt. Icebergs afloat today are made of
snowflakes that have fallen over long ages of time. They embody snows
that drifted down hundreds, or many thousands, or in some cases maybe a
million years ago. The snows fell in polar regions and on cold
mountains, where they melted only a little or not at all, and so
collected to great depths over the years and centuries.

As each year’s snow accumulation lay on the surface, evaporation and
melting caused the snowflakes slowly to lose their feathery points and
become tiny grains of ice. When new snow fell on top of the old, it too
turned to icy grains. So blankets of snow and ice grains mounted layer
upon layer and were of such great thickness that the weight of the upper
layers compressed the lower ones. With time and pressure from above, the
many small ice grains joined and changed to larger crystals, and
eventually the deeper crystals merged into a solid mass of ice.

38 Topaz

Topaz is a hard, transparent mineral. It is a compound of aluminum,
silica, and fluorine. Gem topaz is valuable. Jewelers call this variety
of the stone “precious topaz”. The best-known precious topaz gems
range in color from rich yellow to light brown or pinkish red. Topaz is
one of the hardest gem minerals. In the mineral table of hardness, it
has a rating of 8, which means that a knife cannot cut it, and that
topaz will scratch quartz.

The golden variety of precious topaz is quite uncommon. Most of the
world’s topaz is white or blue. The white and blue crystals of topaz
are large, often weighing thousands of carats. For this reason, the
value of topaz does not depend so much on its size as it does with
diamonds and many other precious stones, where the value increases about
four times with each doubling of weight. The value of a topaz is largely
determined by its quality. But color is also important: blue topaz, for
instance, is often irradiated to deepen and improve its color.

Blue topaz is often sold as aquamarine and a variety of brown quartz is
widely sold as topaz. The quartz is much less brilliant and more
plentiful than true topaz. Most of it is variety of amethyst: that heat
has turned brown.

NOTE:
topaz / 'tэupжz; `topжz/ n (a) [U] transparent yellow mineral 黄玉（矿
物）.
(b) [C] semi-precious gem cut from this 黄玉; 黄宝石.

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39 The Salinity of Ocean Waters

If the salinity of ocean waters is analyzed, it is found to vary only
slightly from place to place. Nevertheless, some of these small changes
are important. There are three basic processes that cause a change in
oceanic salinity. One of these is the subtraction of water from the
ocean by means of evaporation--- conversion of liquid water to water
vapor. In this manner the salinity is increased, since the salts stay
behind. If this is carried to the extreme, of course, white crystals of
salt would be left behind.

The opposite of evaporation is precipitation, such as rain, by which
water is added to the ocean. Here the ocean is being diluted so that the
salinity is decreased. This may occur in areas of high rainfall or in
coastal regions where rivers flow into the ocean. Thus salinity may be
increased by the subtraction of water by evaporation, or decreased by
the addition of fresh water by precipitation or runoff.

Normally, in tropical regions where the sun is very strong, the ocean
salinity is somewhat higher than it is in other parts of the world where
there is not as much evaporation. Similarly, in coastal regions where
rivers dilute the sea, salinity is somewhat lower than in other oceanic
areas.

A third process by which salinity may be altered is associated with the
formation and melting of sea ice. When sea water is frozen, the
dissolved materials are left behind. In this manner, sea water directly
materials are left behind. In this manner, sea water directly beneath
freshly formed sea ice has a higher salinity than it did before the ice
appeared. Of course, when this ice melts, it will tend to decrease the
salinity of the surrounding water.

In the Weddell Sea Antarctica, the densest water in the oceans is formed
as a result of this freezing process, which increases the salinity of
cold water. This heavy water sinks and is found in the deeper portions
of the oceans of the world.

NOTE：
salinity / sэ'linэti; sэ`linэti/
n [U] the high salinity of sea water 海水的高含盐量.
-à>>saline / 'seilain; US -li:n; `selin/
1.adj [attrib 作定语] (fml 文) containing salt; salty 含盐的; 咸的:
* a saline lake 盐湖 * saline springs 盐泉
* saline solution, eg as used for gargling, storing contact lenses, etc
盐溶液（如用于漱喉、存放隐形眼镜等）.
2. n [U] (medical 医) solution of salt and water 盐水.

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40 Cohesion-tension Theory

Atmospheric pressure can support a column of water up to 10 meters high.
But plants can move water much higher; the sequoia tree can pump water
to its very top more than 100 meters above the ground. Until the end of
the nineteenth century, the movement of water in trees and other tall
plants was a mystery. Some botanists hypothesized that the living cells
of plants acted as pumps. But many experiments demonstrated that the
stems of plants in which all the cells are killed can still move water
to appreciable heights. Other explanations for the movement of water in
plants have been based on root pressure, a push on the water from the
roots at the bottom of the plant. But root pressure is not nearly great
enough to push water to the tops of tall trees. Furthermore, the
conifers, which are among the tallest trees, have unusually low root
pressures.

If water is not pumped to the top of a tall tree, and if it is not
pushed to the top of a tall tree, then we may ask: how does it get
there? According to the currently accepted cohesion-tension theory,
water is pulled there. The pull on a rising column of water in a plant
results from the evaporation of water at the top of the plant. As water
is lost from the surface of the leaves, a negative pressure, or tension,
is created. The evaporated water is replaced by water moving from inside
the plant in unbroken columns that extend from the top of a plant to its
roots. The same forces that create surface tension in any sample of
water are responsible for the maintenance of these unbroken columns of
water. When water is confined in tubes of very small bore, the forces of
cohesion (the attraction between water molecules) are so great that the
strength of a column of water compares with the strength of a steel wire
of the same diameter. This cohesive strength permits columns of water to
be pulled to great heights without being broken.