The Earth
The earth is the third planet in the solar system
orbiting the sun. It takes 365.25 days to go round the sun and 24 hours to make
a complete rotation about its axis. The earth is spherically shaped and
surrounded by spheres which form systems.
The Earths Sub Systems (Spheres)
The earth as part of the solar system is made up of other
sub systems which interact among themselves. These system or spheres are; the
atmosphere, biosphere, the geosphere and 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.
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. There is usually an orverlap or transition
between the layers.
Temperature and pressure are some important properties that vary in our
atmosphere. The atmosphere can be seperated 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. Their
properties can be summarized as follows:
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.
-
Weather changes, and cloud formation take place in the
troposphere.
-
Flight paths for planes are found in the troposphere.
-
Atmospheric pressure is highest in this zone
-
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
-
The ozone layer which absorbs UV (ultraviolet radiations) is found
in the stratosphere.
-
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 thereby forming an ionosphere.
-
The high temperatures in the thermosphere is due to direct heat
from the sun.
Generally, atmospheric pressure and level of water vapour decrease
with increase in altitude.
ii.
The Hydrosphere:
The hydrosphere refers to the water found on or near the
earth’s surface. It includes the oceans,
rivers, lakes and all the glaciers of the world. When the hydrosphere is heated, it brings
about evaporation of water bodies and precipitation when it is cooled. Precipitation causes weathering and erosion of
the rocks (geosphere). The earth is the
only planet whose surface is covered by water making up 71% of total surface
area.
iii.
The Biosphere:
The biosphere is all of the living or once-living matter
on earth. It occupies the atmosphere, the hydrosphere and the geosphere.
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