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Geophysics is a branch of science that deals with the physical, chemical, geological, astronomical and other characteristic properties of the earth.It deals with geological phenomena such as the temperature distribution of the earth’s interior, the source, configuration and the geomagnetic field.
Structure and Composition of the Earth
The Structure of the Earth
Describe the structure of the earth
The structure of the earth is composed of three major zones arranged in concentric manner. These are crust, mantle and core.
The crust
Is the outer solid layer o the earth.It is extremely thin(5 to 15km)
compared to the radius of the earth (6,371km).There are two types of crust, namely:
compared to the radius of the earth (6,371km).There are two types of crust, namely:
- Continental crust:
This is heterogeneous and of relatively low density(2 to 2.8 tonnes per
cubic meter).-It is composed mainly of granites and sedimentary rocks. - Oceanic crust: This
is basaltic and more denser (3.0 to 3.1 tonnes per cubic meter). Both
the continental and the oceanic crusts floats on the denser mantle.
Because of its low density,the continental crust floats on the mantle at
a higher elevation, forming the land masses and mountains. The
continental crust is 30 to 70 km thick. The denser oceanic crust floats
at a lower elevation forming oceanic basins.It is about 8km thick. The
boundary between the crust and the mantle is called Mohorocivic discontinuity or simply Moho. It is a zone between one and several kilometers thick.
The mantle
It
begins from the Moho and extends to a depth of 2,900km below the
earth’s surface,up to its boundary with the earth’s core.This boundary
is called the Gutenberg discontinuity.
begins from the Moho and extends to a depth of 2,900km below the
earth’s surface,up to its boundary with the earth’s core.This boundary
is called the Gutenberg discontinuity.
The
mantle contains about 70% of the earth’s mass.It is composed of
rocks,both in solid and mountain states.The upper surface of the mantle
has the temperature of about 870°C,and this temperature increases
downwards through the mantle to about 2,200°C near the core.
mantle contains about 70% of the earth’s mass.It is composed of
rocks,both in solid and mountain states.The upper surface of the mantle
has the temperature of about 870°C,and this temperature increases
downwards through the mantle to about 2,200°C near the core.
The core
Is
the innermost part of the earth.It extends from the Gutenberg
discontinuity to the earth’s geometric centre. The core consists of two
distinct regions namely:
the innermost part of the earth.It extends from the Gutenberg
discontinuity to the earth’s geometric centre. The core consists of two
distinct regions namely:
- The inner core: It is composed of solid material because the high pressure at this depth.-It is composed of iron-nickel alloys.
- The
outer core: Is composed of liquid of molten nickel and iron known as
magma. It extends from the mantle to a depth of about 5,000km below the
earth’s surface.
Activity 1
In groups of five, discuss why the outer core is liquid while the inner core is solid.
The Composition of the Layers of the Earth
Describe the composition of the layers of the earth
Continental
crust is made of granite and sedimentary rocks forming the lands and
the mountains while the oceanic crust forms oceanic basins. Mantle is
made of solids and molten rocks. The outer core is made of molten nickel
and iron called magma while the inner core is solid because of the high
pressure. The crust and the mantle are separated by the mohorovicic
discontinuity.
crust is made of granite and sedimentary rocks forming the lands and
the mountains while the oceanic crust forms oceanic basins. Mantle is
made of solids and molten rocks. The outer core is made of molten nickel
and iron called magma while the inner core is solid because of the high
pressure. The crust and the mantle are separated by the mohorovicic
discontinuity.
The Importance of the Layers of the Earth
Explain the importance of the layers of the earth
Continental
crust forms the land and mountains of the earth on which all human
activities are carried out e.g farming, housing etc. Oceanic crust forms
the base of the oceans and seas on which oceanic water rests and all
aquatic organisms like fishes live. The mantle provides the heat
transfer from the core to the outer layers a process which causes the
volcanic actions and earthquakes.
crust forms the land and mountains of the earth on which all human
activities are carried out e.g farming, housing etc. Oceanic crust forms
the base of the oceans and seas on which oceanic water rests and all
aquatic organisms like fishes live. The mantle provides the heat
transfer from the core to the outer layers a process which causes the
volcanic actions and earthquakes.
Earthquake and Volcanoes
Both
of them, volcano and earthquake are caused by the movement of molten
rock and heat deep inside the earth. These movements are referred to as subterranean movements. Most earthquakes and volcanic activity happen near tectonic boundaries.
of them, volcano and earthquake are caused by the movement of molten
rock and heat deep inside the earth. These movements are referred to as subterranean movements. Most earthquakes and volcanic activity happen near tectonic boundaries.
The Origin of Volcanoes
Explain the origin of volcanoes
Volcanoes
are places where molten rock called magma leaks out through a hole or a
crack in the earth’s crust.Magma originates from the mantle,where high
temperature and pressure cause the rock to melt.When a large pool of
magma if formed,it rises through the denser rock layer towards the
earth’s surface.
are places where molten rock called magma leaks out through a hole or a
crack in the earth’s crust.Magma originates from the mantle,where high
temperature and pressure cause the rock to melt.When a large pool of
magma if formed,it rises through the denser rock layer towards the
earth’s surface.
Magma that has reached the earth’s surface is called lava. Most volcanoes form along constructive and destructive boundaries between tectonic plates.However a few form plate boundaries.
Types of volcanoes
There are two main types of volcanoes, namely:
- Fissure volcanoes:
These occur along the cracks in and between tectonic plates. They can
be many kilometers long. Lava is usually ejected quietly and
continuously,forming enormous plains or plateaus of basaltic volcanic
rock. - Central volcanoes: These have a single
vertical main vent through which mzgm reaches the earth’s surface. They
usually develop a cone shape that builds up from successive layers of
lava and ash.
Classification of volcanoes
Volcanoes are classified into three categories based on their frequency of eruption, namely:
- Active volcanoes: Are those that either erupt constantly or have erupted in recent times. Eg; Oldonyo Lengai.
- Dormant volcanoes: Are those that have been inactive for some time(a few thousand years) but can erupt again. Eg; Mt Kilimanjaroc.
- Extinct volcanoes: They have not erupted in recorded history. They will probably never erupt again.
Effects of Volcanoes
Describe effects of volcanoes
Effects of volcanoes include:
- Landscape:
Most of the earth’s surface is covered with volcanic rocks.Volcanoes
are also responsible for the formation of many mountains and islands. - Vegetation and wildlife:
Volcanic eruption sometimes set the surrounding vegetation into
fire.Wild animals are also killed by being buried into the lava or being
burnt by the forest fires. - Environment:
Volcanic eruptions emit harmful gases into the environment. Such gases
include sulphur dioxide. Some of the gases contribute to global warming
and climate change. - Human life and property: Volcanic eruptions sometimes kill people and destroy property.
- Soil: Volcanoes help in soil formation by bringing important minerals from from deep underground onto the earth’s surface.
- Minerals: Volcanoes also bring valuable minerals to the earth’s surface.The minerals are important economic resources.
The Origin of Earthquake
Explain the origin of earthquake
An
earthquake is a sudden motion or shaking of the earth caused by a
sudden relese of energy that has accumulated within or along the edges
of the earth’s tectonic plates.
earthquake is a sudden motion or shaking of the earth caused by a
sudden relese of energy that has accumulated within or along the edges
of the earth’s tectonic plates.
Earthquakes
happen when rocks in the earth’s crust move suddenly, shaking the
earth.Earthquake also occur as a result of movement of magma at
constructive boundaries under volcanoes and where continental plates
collide and push mountain ranges.
happen when rocks in the earth’s crust move suddenly, shaking the
earth.Earthquake also occur as a result of movement of magma at
constructive boundaries under volcanoes and where continental plates
collide and push mountain ranges.
How earthquake occur
Earthquakes
mostly occur on or near the boundaries between tectonic plates.However
,earthquakes can also occur far from plate boundaries. Such earthquakes
probably occur as a result of faults formed millions of years ago.
mostly occur on or near the boundaries between tectonic plates.However
,earthquakes can also occur far from plate boundaries. Such earthquakes
probably occur as a result of faults formed millions of years ago.
Pressure
liquid builds between them until the friction force holding the plates
together gives way.The plates move suddenly,releasing the pressure or
energy and then holds together again. This sudden jerk is what is felt
as an earthquake.
liquid builds between them until the friction force holding the plates
together gives way.The plates move suddenly,releasing the pressure or
energy and then holds together again. This sudden jerk is what is felt
as an earthquake.
The point within the earth where an earthquake begins is called the hypocenter or the focus of the earthquake. Earthquake rarely occur along constructive plate boundaries.
Seismic waves
This refers to the energy released by an earthquake. They are grouped into three categories:
- Primary waves or p-waves: Are the first waves released from the hypocenter. They are felt as a sudden jolt.
- Secondary waves or s-waves: These arrive a few soconds later after p-waves.They are felt as a series of side-to-side tremors.
- Surface
waves.-They radiate outward from the point on the earth’s surface
directly above the hypocentre. This point is called the epicentre of the earthquake.
There are two types of surface waves:
- Reyleigh waves- create a rolling movement that makes the land surface move up and down.
- Love
waves- make the ground shift from side to side. It is the surface waves
that demage to surface structure such as buildings and hydroelectric
power plants.
The Principle of Measurement
Describe the principle of measurement of earthquake
The nature of an earthquake is usually described by measuring two properties, namely the magnitude and intensity.
The magnitude of an earthquake is a measure of the energy it releases. It is usually measured on the Richter scale.
The
Richter scale magnitudes are based on a logarithmic scale(base 10).The
intensity of an earthquake is a measure of its strength based on the
changes it causes to the landscape.The intensity is usually measured on
the Modified Mercalli scale.The scale is calibrated 1 to 12.
Richter scale magnitudes are based on a logarithmic scale(base 10).The
intensity of an earthquake is a measure of its strength based on the
changes it causes to the landscape.The intensity is usually measured on
the Modified Mercalli scale.The scale is calibrated 1 to 12.
Note:An
earthquake can have only one magnitude. However its intensity reduces
as the seismic waves spread out from the hypocentre,just the same way
the loudness of a sound changes as you move away from the source.
earthquake can have only one magnitude. However its intensity reduces
as the seismic waves spread out from the hypocentre,just the same way
the loudness of a sound changes as you move away from the source.
The Seismograph:Is
an instrument used to record ground movements caused by earthquakes. It
measures ground oscillations by recording the relative motion between a
pendulum and the ground. It is also possible to use the ratio between
the deflection and the of the pendulum and the acceleration of the of
the ground to record an earthquake.
an instrument used to record ground movements caused by earthquakes. It
measures ground oscillations by recording the relative motion between a
pendulum and the ground. It is also possible to use the ratio between
the deflection and the of the pendulum and the acceleration of the of
the ground to record an earthquake.
Precaution against Earthquake Hazards
Identify precaution against earthquake hazards
Earthquakes hazards
The following are some of the hazards associated with earthquakes:
- Landslides
- Tsunamis
- Collapsing buildings
- Fire outbreak
- Backward rivers
Earthquake warning signs
The following are important signs that are observed before an earthquake occurs:
- Thermal indicator
- Water indicator
- Seismo electromagnetic indicator
- Animal indicator
- Human indicator
Precautions to be taken during an earthquake
The
following are some precautions that can be taken to minimise injuries
or death of human beings in the event of an earthquake:
following are some precautions that can be taken to minimise injuries
or death of human beings in the event of an earthquake:
- If
you are indoors during an earthquake ,drop,cover and hold on.Get under a
desk,table or a bench.Hold on to one of the legs and cover your eyes.If
there is no desk or table nearby, sit down against an interior wall. - Pick a safe place where things will not fall on you-away from windows or tall heavy furniture.
- Do
not run outside when the earthquake happens because bricks, roofing and
other materials may fall from buildings during and immediately after an
earthquake, injuring persons near the building. - Wait in your
safe place until the shaking stops, then check to see if you are hurt.
You will be better able to help others if you take care of yourself
first,then check on the people around you. - Move carefully and
watch out for things that have fallen or broken creating hazards. Be
ready for additional earthquakes called after shocks. - Be on the lookout for fires. Fire is the most common earthquake-related hazard due to damaged gas and electrical lines.
- If
you must leave a building after the shaking stops, use the stairs and
not elevator. Earthquakes can cause fire alarms and fire sprinklers to
go off. You will not be certain whether there is a real threat of fire.
As a precaution,use the stairs. - If you are outside during an
earthquake,stay outside. Move away from buildings, trees, streetlights
and power lines. Crouch down and cover your head. Bricks,roofing and
other materials can fall from buildings, injuring persons nearby.Trees,
streetlights and poor lines may also fall, causing damage or injury.
Structure and Composition of the Atmosphere
The Vertical Structure of the Atmosphere
Describe the vertical structure of the atmosphere
The
atmosphere is a layer of gases containing numerous small suspended
solid and liquid particles surrounding the earth.It has no outer
boundary,it just fades into space.The dense part of the atmosphere lies
within 30km above the earth’s surface.
atmosphere is a layer of gases containing numerous small suspended
solid and liquid particles surrounding the earth.It has no outer
boundary,it just fades into space.The dense part of the atmosphere lies
within 30km above the earth’s surface.
The
atmosphere is divided into regions based on its thermal characterestics
(temperature changes),chemical composition, movement and density. It is
divided into five regions, which are:
atmosphere is divided into regions based on its thermal characterestics
(temperature changes),chemical composition, movement and density. It is
divided into five regions, which are:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
The Composition of the Atmosphere
Describe the composition of the atmosphere
Troposphere
This
is the region nearest to the earth’s surface which extends to an
altitude up to 10 km above the poles and 20km above the equator.It is
the most dense part of the atmosphere(80% by mass of the atmosphere)
which contains most of the atmosphere’s water vapour.
is the region nearest to the earth’s surface which extends to an
altitude up to 10 km above the poles and 20km above the equator.It is
the most dense part of the atmosphere(80% by mass of the atmosphere)
which contains most of the atmosphere’s water vapour.
The
temperature in this region decreases with altitude at an average rate
of 6°C/km.It encourages the change of weather(most of weather phenomenon
occur in the troposphere).Clouds and rain are formed within this
region.
temperature in this region decreases with altitude at an average rate
of 6°C/km.It encourages the change of weather(most of weather phenomenon
occur in the troposphere).Clouds and rain are formed within this
region.
The
boundary which separates the tropospher from the the stratosphere is
called the tropopause. At the tropopause,the temperature stop decreasing
with altitude and becomes constant. The tropopause has an average
height of about 10km.
boundary which separates the tropospher from the the stratosphere is
called the tropopause. At the tropopause,the temperature stop decreasing
with altitude and becomes constant. The tropopause has an average
height of about 10km.
Stratosphere
It starts from the tropopause and extends to 50km high.It is more stable,drier and less dense compared to troposphere.
The
temperature slowly increases with altitude due to the presence of ozone
layer which absorbs ultraviolet rays from the sun. The ozone layer lies
in the middle of the stratosphere between 20 and 30km. Ozone is
triatomic(three-molecules) form of oxygen.
temperature slowly increases with altitude due to the presence of ozone
layer which absorbs ultraviolet rays from the sun. The ozone layer lies
in the middle of the stratosphere between 20 and 30km. Ozone is
triatomic(three-molecules) form of oxygen.
The
stratosphere together with with troposphere are collectively known as
the lower atmosphere.The boundary which separates the stratosphere from
the outer layer is called the stratopause.
stratosphere together with with troposphere are collectively known as
the lower atmosphere.The boundary which separates the stratosphere from
the outer layer is called the stratopause.
Advantages of stratosphere
It
absorbs the ultraviolet radiations which would otherwise reach the
earth’s surface which is harmful to both plants and animals.
absorbs the ultraviolet radiations which would otherwise reach the
earth’s surface which is harmful to both plants and animals.
It
prevents large storms from extending much beyond the troposphere due to
its stability. Planes also fly within this layer because it has strong
steady horizontal winds which are above the stormy weather of the
troposphere.
prevents large storms from extending much beyond the troposphere due to
its stability. Planes also fly within this layer because it has strong
steady horizontal winds which are above the stormy weather of the
troposphere.
Mesosphere
It
starts just above the stratosphere and extends to 85km high.The
temperature at this layer decreases with altitude.The lowest temperature
of the atmosphere occurs within this region(-90°C).
starts just above the stratosphere and extends to 85km high.The
temperature at this layer decreases with altitude.The lowest temperature
of the atmosphere occurs within this region(-90°C).
Is
the layer where most meteors burn while entering the earth’s
atmosphere.The boundary which separates the mesosphere from the
thermosphere is called the mesopause.
the layer where most meteors burn while entering the earth’s
atmosphere.The boundary which separates the mesosphere from the
thermosphere is called the mesopause.
Thermosphere
It
is just above the mesopause and extends up to 690km high. The
temperature increases with altitude due to the sun’s heat.The
temperature in this region can go as high as1727°C and chemical
reactions occur faster in this region than on the earth’s surface.
is just above the mesopause and extends up to 690km high. The
temperature increases with altitude due to the sun’s heat.The
temperature in this region can go as high as1727°C and chemical
reactions occur faster in this region than on the earth’s surface.
This
layer is also known as the upper atmosphere. The lower part of the
thermosphere,from 80 to 550km above the earth’s surface, contains the
ionosphere. This is a region containing a high concentration of charged
particles called ions and free electrons.
layer is also known as the upper atmosphere. The lower part of the
thermosphere,from 80 to 550km above the earth’s surface, contains the
ionosphere. This is a region containing a high concentration of charged
particles called ions and free electrons.
Importance of ionosphere
The
large number of free electrons in the ionosphere allows the propagation
of electromagnetic waves. It absorbs the dangerous radiations like
X-rays and extreme ultraviolet(EUV) radiation. It plays an important
role in communition of radio waves.
large number of free electrons in the ionosphere allows the propagation
of electromagnetic waves. It absorbs the dangerous radiations like
X-rays and extreme ultraviolet(EUV) radiation. It plays an important
role in communition of radio waves.
Exosphere
Is
the outermost region of the atmosphere.In this region,the atmospheric
gas pressure is very low such that light atoms such as hydrogen and
helium may acquire sufficient energy to escape the earth’s gravitational
pull.
the outermost region of the atmosphere.In this region,the atmospheric
gas pressure is very low such that light atoms such as hydrogen and
helium may acquire sufficient energy to escape the earth’s gravitational
pull.
The
upper part of the exosphere is called magnetosphere.The motion of ions
in this region is strongly constrained by the presence of the earth’s
magnetic field.This is the region where satellites orbit the earth.
upper part of the exosphere is called magnetosphere.The motion of ions
in this region is strongly constrained by the presence of the earth’s
magnetic field.This is the region where satellites orbit the earth.
The Importance of Various Layers of the Atmosphere
Explain the importance of various layers of the atmosphere
The importance of the atmosphere include the following:
- The troposphere controls the climate and ultimately determines the quality of life on the earth.
- The
troposphere is important for life on earth. The layer contains gases
which include oxygen which is used for respiration by animals and carbon
dioxide which is used by plants in photosynthesis. The nitrogen found
in this laye also provides an inactive environment for many chemical
processes to take place. The gases also support many important chemical
processes such as combustion,weathering and oxidation. - The stratosphere prevents harmful ultraviolet radiation from reaching the earth.
- The mesosphere,thermosphere and exosphere also prevent harmful radiation such as cosmic rays from reaching the earth’s surface.
- Communication is also made possible by some layers of the atmosphere, specifically the ionosphere.
The Greenhouse Effect and Global Warming
The Greenhouse Effect
Explain the greenhouse effect
Global
warming is the increase of the average temeratures near or on the
surface of the earth as a result of what is known as the greenhouse
effect. The effect is caused by greenhouse effect. These gases are
produced from natural and industrial processes.
warming is the increase of the average temeratures near or on the
surface of the earth as a result of what is known as the greenhouse
effect. The effect is caused by greenhouse effect. These gases are
produced from natural and industrial processes.
The greenhouse effect is the process in which the emission of radiation by the atmosphere warms the earth’s surface.
When
heat from the sun reaches the earth’s surface in form of sunlight,some
of it is absorbed by the earth.The rest is radiated back to the
atmosphere at a longer wavelength than the incoming sunlight.Some of
these longer wavelengths are absorbed by greenhouse gases in the
atmosphere before they are lost to space.The absorption of this
long-wave radiant energy warms the atmosphere.
heat from the sun reaches the earth’s surface in form of sunlight,some
of it is absorbed by the earth.The rest is radiated back to the
atmosphere at a longer wavelength than the incoming sunlight.Some of
these longer wavelengths are absorbed by greenhouse gases in the
atmosphere before they are lost to space.The absorption of this
long-wave radiant energy warms the atmosphere.
The
greenhouse gases act like a mirror, reflecting back to the earth some
of the heat energy which would otherwise be lost to space.
greenhouse gases act like a mirror, reflecting back to the earth some
of the heat energy which would otherwise be lost to space.
Sources of Greenhouse Effect
Identify sources of greenhouse
Sources of greenhouse effect include:
- Carbondioxide
- Clearing and burning of vegetation
- Burning of fossil fuel
- Methane
- Dinitrogen oxide
- Chlorofluorocarbons(CFCs)
The Occurence of Global Warming
Explain the occurrence of global warming
Global
warming is primarily a problem of too much carbon dioxide (CO2) in the
atmosphere—which acts as a blanket, trapping heat and warming the
planet. As we burn fossil fuels like coal, oil and natural gas for
energy or cut down and burn forests to create pastures and plantations,
carbon accumulates and overloads our atmosphere. Certain waste
management and agricultural practices aggravate the problem by releasing
other potent global warming gases, such as methane and nitrous oxide.
warming is primarily a problem of too much carbon dioxide (CO2) in the
atmosphere—which acts as a blanket, trapping heat and warming the
planet. As we burn fossil fuels like coal, oil and natural gas for
energy or cut down and burn forests to create pastures and plantations,
carbon accumulates and overloads our atmosphere. Certain waste
management and agricultural practices aggravate the problem by releasing
other potent global warming gases, such as methane and nitrous oxide.
The Consequences of Global Warming
State the consequences of global warming
Effects of Global Warming
- Increase in the temperature of the oceans.
- Rise in sea levels.
- Change in world’s climatic pattern.
- Acidification of the oceans.
- Extreme weather events.
- Higher or lower agricultural yields.
- Melting of Arctic ice and snowcaps. This cause landslides, flash floods and glacial lake overflow.
- Extinction of some animal and plant species.
- Increase in the range of disease vectors, that is,organisms that transmit diseases.
