-
The Earth's Atmosphere
Unless
it's raining or the wind is blowing,
we
don't usually pay much attention to the
atmosphere,
the
blanket
of
air
that
surrounds
the
Earth.
Yet,
without
the
atmosphere, the Earth would be a
desolate
(
荒芜的
)
planet withno signs of life!
The
atmosphere
plays
several
roles
in
helping
to
make
life
possible.
First,
the
atmosphere
provides
the
three
gases
necessary
for
life:
oxygen,
nitrogen,
and
carbon
dioxide.
All
animals,
including
ourselves,
breathe
oxygen.
Nitrogen
and
carbon
dioxide
are
both
needed
for
plant
growth.
Less important atmospheric gases
include argon, neon, helium, and
hydrogen.
Second, the atmosphere also
protects us
from
most
of
the
sun's
high-energy
ultraviolet
light rays, which are harmful to
life.
Although these rays are only a small
part of the sunlight striking the
Earth, they
are known to be very
dangerous. However,
99
percent
of
all
ultraviolet
rays
are
absorbed
before
they
reach
the
Earth's
surface.
They
are
absorbed
by
an
atmospheric
gas,
called
ozone,
a
type
of
oxygen
gas. The ozone layer surrounds the
Earth but is much thinner over the
North
and South Poles than over other
regions of
the Earth.
The
one percent of the ultraviolet light
in
the
atmosphere
that
does
reach
the
Earth's surface is known
to cause sunburn
and
is
now
believed
to
also
cause
skin
cancer
in
many
people.
Because
of
this
,
doctors
recommend
that
people
limit
the
amount
of
time
they
spend
in
direct
sunlight and wear a suntan lotion (
防晒油
)
that blocks
the ultraviolet rays when they
do
sunbathe.
Finally,
the
atmosphere
generates
all
types
of
weather
such
as
clear
blue
skies
and
storms.
It
acts
as
a
huge
energy
machine,
changing
sunlight
into
other
forms of energy such
as heat and wind. As
part
of
this
role,
the
atmosphere
regulates
the temperature on the Earth's surface.
First
it
allows
only
46
percent
of
the
sunlight
striking it to pass through and
actually reach
the Earth's surface.
Second, carbon dioxide
gas in the
atmosphere controls the amount
of
warmth
on
the
Earth's
surface
that
is
allowed
to radiate (
发散
)
back into space.
By
these
two
controlling
devices,
the
atmosphere
regulates
the
Earth's
surface
temperature.
Choose
the
best
answers
to
the
following
questions.
1.
Which of the following is true
according to
the passage?
A.
The ozone
layer is much thicker over
North
America than over the North
Pole.
B.
Ozone is a
type of a nitrogen gas.
Ozone can
absorb some ultraviolet
rays before
they reach the Earth's
surface.
C.
D.
Ozone can protect us from anything
harmful to our life.
2.
The main idea
of the third paragraph is
that __
.
A.
the Earth is surrounded by a layer of
ozone
B.
99 percent of all ultraviolet light
rays
that reach the Earth's surface are
absorbed by the ozone layer
C.
the
o
zone layer protects people
from the
sun's high-energy ultraviolet
light rays
D.
ozone
is an atmospheric gas
which surrounds the Earth
3.
According to
the article, carbon
dioxide
________________________
A.
is a less important atmospheric gas
controls the amount of warmth on
the Earth's surface
B.
C.
allows only 46 percent of sunlight to
reach the Earth's surface
D.
acts
l
ike a huge energy machine
Doctors suggest that ______ .
people should stay away from the
sunlight to protect themselves from
the sunburn
4.
A.