Suggested Teacher's Guide for Discussion

1. Suggested Teacher’s Guide for Discussion
Grade 7 Science
MA. RACHEL B. ESPINO
Buhatan National High School
Purok Marcos, Buhatan, Sorsogon City

2. The Earth is enveloped in air
 The Earth is
enveloped in air
called atmosphere.
The pull of the
Earth keeps this
ocean of air close to
it.

3.  Without the
atmosphere, life
cannot exist on Earth,
for the atmosphere
contains oxygen – the
life-sustaining gas.
From the air, plants get
carbon dioxide needed
to manufacture food
that are in turn needed
by animals in order to
live.

4. The layers of air
also protects us
from intense
radiation by day
and too much
loss of heat by
night.

5.  Weather, the natural phenomenon that greatly
influences life on Earth, occurs in the atmosphere.

6.  The gases
comprising the
atmosphere filter
the sun’s
ultraviolent light
which may prove
dangerous when
received at its full
strength.

7. COMPOSITION OF THE EARTH’S
ATMOSPHERE
 The Earth’s atmosphere is
composed of the following
molecules: nitrogen (78%),
oxygen (21%), argon (1%),
and then trace amounts of
carbon dioxide, neon,
helium, methane, krypton,
hydrogen, nitrous oxide,
xenon, ozone, iodine,
carbon monoxide, and
ammonia. Lower altitudes
also have quantities of
water vapor.
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8. COMPOSITION OF THE EARTH’S
ATMOSPHERE
 The Earth’s atmosphere is composed of the following
molecules: nitrogen (78%), oxygen (21%), argon (1%), and
then trace amounts of carbon dioxide, neon, helium,
methane, krypton, hydrogen, nitrous oxide, xenon, ozone,
iodine, carbon monoxide, and ammonia. Lower altitudes
also have quantities of water vapor.
 The atmosphere we have today is very different from the
Earth’s early atmosphere. When the planet first cooled
down 4.4 billion years ago, volcanos spewed out steam,
carbon dioxide and ammonia, and it was 100 times as dense
as today’s atmosphere.
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9. THE LAYERS OF THE ATMOSPHERE
 Temperature changes so much with altitude that one
can identify major divisions or layers of the
atmosphere based on temperature variations.
However, scientists use the average atmosphere as the
basis of dividing the atmosphere into 5 layers. This
temperature profile is an average of temperature
profiles obtained from all over the globe over a long
period of time.

11. Troposphere
 The bottom layer closest to the Earth is the
troposphere. It extends up to an altitude of 16 to 18 km
above sea level at the equator and around 8 km at the
poles. The air becomes colder as the distance from the
ground increases, therefore the upper part of the
troposphere is not warmed by sunlight. Most of the
visible light incident on Earth pass through the
atmosphere and reach Earth’s surface, causing it to
become warm and emit infrared radiation.

13.  Gases in the air such as carbon dioxide and water vapor
absorb infrared radiation. Absorption of infrared
radiation from the surface warms the lower
atmosphere. Thus, the troposphere is not warmed from
above but from below. Earth’s surface serves as the heat
source for the decreasing temperature since this means
moving away from the heat source. This results in a
decreasing temperature profile as altitude in the
troposphere increases.

15.  Note that at the top of
each layer, there is a
“pause” where the
temperature changes
abruptly. At the top of the
troposphere is the
tropopause, a region
where the temperature
stops decreasing. The
tropopause is the highest
in the tropical areas and
lowest near the poles.

16. Stratosphere
 The next layer above the troposphere is the stratosphere.
It extends from the top of the troposphere to a height of
about 40 km.
 In contrast to the troposphere, the temperature in the
stratosphere rise with increasing altitude. This is because
the ozone layer found at the stratosphere highly absorbs
UV radiation from the sun.

18.  Absorption of UV warms the surrounding air, leading
to an increase of temperature. UV absorption is
greatest at the uppermost level of the stratosphere,
hence air temperature is also highest in this region.
Absorption of UV at higher levels is lower, the amount
that is available at lower levels of the atmosphere

20.  The air is much thinner in the stratosphere and it is
clear and cloudless. This is the layer where jet planes
and manned balloons fly. The “pause” at the top of the
stratosphere is the stratopause.

21. Mesosphere
 Directly above the stratosphere extending from 50 to
10 km above the Earth’s surface is the mesosphere. It is
a cold layer where the temperature generally decreases
with increasing altitude. Here in the mesosphere, the
atmosphere is very rarefied, meaning it has less
oxygen. Nevertheless, it is thick enough to slow down
meteors hurtling into the atmosphere where they burn
up, leaving fiery trails in the night sky. With no gas
that absorbs sunlight in this layer, the temperature
decreases with height.

24. Thermosphere
 The thermosphere extends to about 87 to 100 km. In
the thermosphere, the temperature change is small. It
increases gradually from about 100 to 110 km. From 100
km to the end of the layer, the temperature steadily
increases with height.
 In the thermosphere, temperature increases with
altitude due to the absorption of high-energy radiation
from the sun.

26. Exosphere
 The upper limit of our
atmosphere is the
exosphere. This layer of
the atmosphere merges
into space. Satellites are
stationed in this area,
500 km to 1,000 km from
Earth.

27. Suggested Videos:
 The Earth’s Atmosphere
https://youtu.be/WVAZcphSz7k?list=PLXZAD5CEPE-
vkd8GpvOpVakZJK2F-v8nN
 Reveal the Earth’s Atmosphere
https://youtu.be/1YAOT92wuD8?list=PLXZAD5CEPE-
vkd8GpvOpVakZJK2F-v8nN