The Earth
The earth is the third planet from the sun in the solar
system. It takes 365.25 days to go round the sun and 24 hours to make a
complete rotation on its axis. It is the only planet known to support
life. The earth is spherical with near
flat ends at the poles and surrounded by spheres which form systems. The shape of the earth is described as GEOID.
The Earth’s Sub systems (spheres)
The earth as part of the solar system is made up of other
sub systems which interact among themselves. These systems or spheres include;
the atmosphere, biosphere, the geosphere and the hydrosphere.
i.
The Atmosphere:
The atmosphere is a thick envelop of
gases that covers the earth.
It measures
up to about 2000 km in thickness and is made up of mainly Nitrogen, oxygen, carbondioxide,
water vapour and Argon, and also other solid substances such as dust particles,
bacteria and salts blown from the sea.
(Find out
the percentage by volume of gases that make up the atmosphere)
The Earth’s atmosphere can be divided into several layers depending upon
what properties are considered. Although each layer has a unique set of
properties, they cannot be finely distinguished.
Temperature and pressure are some important properties that vary in our
atmosphere. Based on temperature changes, the atmosphere can be broken into
four major layers, and three small intermediate layers that serve as transition
regions from one layer to the next. These
layers are the troposphere, tropopause, the stratosphere and stratopause, the
mesosphere and mesopause, and the thermosphere.
We will base our studies on the major layers which are the troposphere,
the mesosphere and the atmosphere.
a)
The troposphere:
-
It is the layer of the atmosphere that is closest to the ground.
This is the layer that we live in.
-
It is about 11 km thick
-
In the troposphere, the higher you go from the ground, the colder
it becomes. This is because as light
from the Sun reaches the ground, some of it is absorbed and converted into thermal
energy (the energy associated with heat). This thermal energy spreads
through the atmosphere by conduction and convection. The result is that, it gets cooler as we go to higher altitudes.
-
Weather changes, and cloud formation take place in the
troposphere.
-
Flight paths for planes are found in the troposphere.
-
The transition zone between the troposphere and the stratosphere
is the tropopause.
b)
The
stratosphere;
-
This is the layer above the troposphere.
-
It extends from about 11 km to 50km above sea level (what is the
thickness of the stratosphere?)
-
The ozone layer which absorbs UV (ultraviolet radiations) is found
in the stratosphere. The stratosphere
therefore acts as a protective layer, preventing UV radiations from reaching
the earth’s surface. (What are some of the effects of UV radiations
especially on man?).
-
The presence of the ozone layer in the stratosphere causes temperatures
to rise as you go higher in the stratosphere.
-
The stratopause is the transition region between the stratosphere
and the mesosphere.
c)
The
mesosphere;
-
This is the layer above the stratosphere.
-
It extends from about 50km to 85 km.
-
It is the coldest layer (about -1300 C) and
temperatures drop as you go higher from the stratosphere.
-
The mesopause separates the mesosphere from the thermosphere.
d)
The
thermosphere;
-
It is the outermost layer of the atmosphere and extends from about
90 km to about 750 km. It is therefore
the thickest layer of the atmosphere.
-
Temperatures increase from the mesopause into the thermosphere to
about 1650oC.
-
The high temperatures cause atmospheric gases in the thermosphere to
be ionised (stripped of their electrons) thereby forming an ionosphere.
-
The high temperatures in the thermosphere is due to direct heat
from the sun.
Scientists consider the atmosphere to be about 2000km thick. Geologically, the atmosphere is important
because it facilitates the alteration of rocks by especially surface
processes.
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