GEOPHYSICS

GEOPHYSICS

GEOPHYSICS
Geophysics:  Is the branch of science that is concerned with the physical, chemical, geological, astronomical and other characteristic properties of the earth.
OR
Is the study of the physical properties of the earth.

INTERIOR STRUCTURE OF THE EARTH

The structure of the earth is composed of three major zones arranged in a concentric manner.
  • The crust
  • The manner
  • The core
THE CRUST

Is the outer solid layer of the earth. It is the thinnest layer compared to other two components. Its thickness is as out 6 to 40km (5 to 30 miles) compared to the radius of the Earth 6400km.

TYPES OF CRUST
  • Continental crust (SIAL)
  • Oceanic crust (SIMA)
CONTINENTAL CRUST (THE SIAL)

Is the outer most layer of the earth which forms the continents. The SIAL composed of silica and Aluminium compound.

Seas, oceans, rivers and lakes are interrupts SIAL.

OCEANIC CRUST (THE SIMA)
  • Is the inner part of the crust it is composed by silica and magnesium. It is denser than SIAL.
  • The SIMA forms the oceanic floor.
  • The SIAL and SIMA is separated by layer called(Conrad discontinuity”
THE MANTLE
  • Is the layer found between the earth’s crust and the core. It extends to a depth of 2900km below the earth’s surface from the Mohorovic discontinuity. It is denser than earth’s crust.
  • The layer which separates the crust and mantle is called Mohorovic Discontinuity”
  • The Mantle contains about 70% of the Earth’s mass.
PARTS OF MANTLE
  • The upper Mantle
  • The lower Mantle
The temperature of the upper Mantle is about 870°C and increases to 2,200°C of the inner (lower) mantle.
The Mantle is composed by rocks that are said to be in a plastic state.

THE CORE
Is the inner most part of the Earth’s interior.
Have two layers
Liquid outer core
Solid inner core
 LIQUID OUTER CORE
The layer composed of a liquid of molten nickel and iron called MAGMA. It extends to a depth about 5000km below the earth from the Mantle.

SOLID INNER CORE
The layer composed of a solid of iron – nickel alloys. It is solid because of the high pressure, the inner core is very hot, and its temperature is about 6000°C.
The layer which separates the Mantle and the core is called. “Gutenberg discontinuity” 

TECTONIC PLATES
Are huge pieces creates by cracks of the earth’s crust and part of the Mantle.
They float on top of the semi- Molten rocks underneath. They move about at a very slow speed.
These Tectonic plate movements have split the continents.

BOUNDARY
Are lines where two tectonic plates meet.

TYPES OF BOUNDARIES
  • Destruction boundaries.
  • Constructive boundaries.
  • Conservative boundaries.

DESTRUCTIVE BOUNDARY
Is the boundary found at edges of two plates moving towards each other.


CONSTRUCTIVE BOUNDARIES
Are boundaries formed at the edges of two plates moving away from each other.


CONSERVATIVE BOUNDARIES
Are boundaries formed when two plates slides past each other without moving a part or towards each other.

CLASS ACTIVITY
  1. Differentiate Mohorovic, Conrad and Gutenberg discontinuities.
  2. Describe the interior structure of the earth.
  3. Explain why the inner core of the earth is solid while the outer core is liquid even through the temperature is high.
VOLCANOES

VOLCANOES are places where molten rock called Magma leaks out through a hole or crack in the
                        earth’s crust.

Magma: Is the Molten rock containing liquids, crystals and dissolved gases that forms within the upper part of the earth’s Mantle and crust.

Note:
Volcanoes are caused by movement of molten rock and heat deep inside the earth.

Lava: Is a magna (Molten rock) that reaches the earth’s surface during a volcanic eruption.

Most of volcanoes form along constructive and destruction boundaries between tectonic plate.


VOLCANOES AT DESTRUCTIVE BOUNDARIES
When an ocean plate plunges under another plate, the ocean plate rubs the plate above it and get hot, hence rocks melts resulting in magma under the upper plate.

The Magma forces its way through weak points in the crust, hence creates lines of volcanoes called (the ring of Fire(. Eg. Ring of fire along the west coast of South America, and North America through Japan, the Philippines and New sea land.


VOLCANOES AT CONSTRUCTIVE BOUNDARIES
These are formed where two plates move a part at the boundary. Magma moves up from underneath to fill the gap left by the separating plates. The Mid – Atlantic Ocean is a continuous volcano that is thousands of kilometers long.

HOT-SPOT VOLCANOES
Are volcanoes erupted thousands of kilometers away from tectonic plate boundaries. These eruptions occur over places in the Mantle that are hotter than normal.
e.g. : Nyamulagira volcano in Congo is a hot- spot volcano.

TYPES OF VOLCANOES
  • Fissure volcanoes
  • Central volcanoes
FISSURE VOLCANOES
These occur along cracks in and between tectonic plates.


Lava is usually affected quietly and continuously, forming enormous plain or plateaus of basaltic volcanic rock.

CENTRAL VOLCANOES
These volcanoes have a single vertical main vent through which Magma 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.

  • ACTIVE VOLCANOES: Are volcanoes that either erupt constantly or have erupted in recent times an example is Oldonyo lengai volcano.
  • DOMANT VOLCANOES: Are those that either erupt constantly or have erupted in recent times (a few thousand years) but erupted again. An example is Mt Kilimanjaro.
  • EXTINCT VOLCANOES: Are volcanoes that have not erupted in recorded history. They will probably never erupt again.
EFFECTS OF VOLCANOES
  • Volcanoes are responsible for the formation of many mountains and Islands.
  • Volcanic eruptions destroy vegetation such as forests, woodlands and grass lands.
  • Volcanic eruptions cause death of wild animals
  • Volcanic eruptions cause environmental pollution. Some of the harmful gases such as sulphurdioxide pollute environment.
  • Volcanic eruption cause killing of people and destroy property.
  • Volcanic eruption help in soil formation by bringing important soil minerals from deep underground on to the earth’s surface.
  • Volcanic eruption brings valuable mineral to the earth’s surface.
  • Volcanic eruption helps to generate geothermal power.
EARTH QUAKES
Are saddened earth movements or vibration in the crust.

Seismology: Is the scientific study and interpretation of the earth quakes.

CAUSES OF EARTH QUAKES
  • Earth quakes are caused by movement or sliding of tectonic plates. When tectonic plate met they cause stress and fracture of the crustal rocks, hence causes release of energy which generates shock waves which shake the earth.
  • Are also caused by volcanic eruption, where high pressure in the crust pushes out Magma strongly and causes vibrations.
  • Also locally earth quakes may be caused by mass wasting, falling of meteors from the space, human activities.
NOTE:-
When earth quakes occur in oceans they creates oceanic waves called(Tsunami(

IMPORTANT TERMS
  • FOCUS
                Is the point where the earth quake originates. Sometimes called “Hypocenter”
  • EPICENTER
Is the point where the shock waves (Earth quakes) hit first and give rise to an earth quake.
             
SEISMIC WAVES
Are waves generated by the earth quakes.

TYPES OF SEISMIC WAVES
  • Body waves
  • Surface waves
BODY WAVES
Are seismic waves that travel within the earth is crust.

TYPES OF BODY WAVES
  • PRIMARY WAVES(P-WAVES)
Are longitudinal waves that are very fast and they can travel far from interior.

PROPERTIES OF PRIMARY WAVES
  • Are the first waves released from the focus.
  • They are very fast and very strong.
  • They cause the crust to move back and forth in the direction of wave movement.
  • They can travel through both liquid and solid matter.
  • They are longitudinal waves. They are like sound waves.

  • SECONDARY WAVE(S-WAVES)
Are transverse waves that cause the crustal rock to move from side to side.
They are transverse waves. They like light waves.

PROPERTIES OF SECONDARY WAVES
  • They are medium speed waves.
  • They affect one side of epicenter.
  • They cause the crustal rocks to move from side to side at a right angle to the direction of wave movement.
  • They are transverse waves. They like light waves.

They cannot travel through liquid matter.

SURFACE WAVES
Are seismic waves that travel through the surface rocks.

TYPES OF SURFACE WAVES
  • Rayleigh(R) waves
  • Love (L) waves
RAYLEIGH WAVES
Are surface waves that cause the surface rock to have vertical circular movements.

PROPERTIES OF RAYLEIGH WAVES
  • They are very destructive as they occur on the surface.
  • Create rolling movements that makes the land surface move up and down like water waves.
LOVE WAVES (L-WAVES)
Are surface waves that cause the surface to move from side to side at a right angle to the direction of
wave movement.
PROPERTIES OF LOVE WAVES (L-WAVES)
  • They make the ground shift side to side
  • They produce entirely horizontal motion
  • It is surface waves that do damage to surface structure such as buildings and hydroelectric power plants
SEISMOGRAPH
Is an instrument used to record ground movements caused by earth quakes.


STRUCTURE AND COMPOSITION OF THE ATMOSPHERE

ATMOSPHERE: Is a layer of gases containing numerous small suspended solid and liquid particles.

STRUCTURE OF ATMOSPHERE
The atmosphere is divided into regions based on its thermal (temperature changes) characteristics, chemical, composition, movement and density.

LAYERS OF ATMOSPHERE
  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
  • Exosphere
TROPOSPHERE
Is the layer (region) nearest to the Earth, it extends to an altitude of up to 10km above the poles and
20km, above the equator


PROPERTIES OF TROPOSPHERE

  • Has the most density. Is the region of the most density part of the atmosphere.
  • It contains most of the atmosphere’s water – vapour.
  • The temperature decreases with the increase of altitude at an average rate of 6°C/km.
  • Most weather phenomenon occurs in the troposphere.
  • Clouds and rain are formed within this region.
NOTE:
The boundary which separates the troposphere and the stratosphere is called “Tropopause”.
Temperature at the Tropopause remains constant.

STRATOSPHERE
The stratosphere starts from the tropopause and extends to 50km high.

PROPERTIES OF STRATOSPHERE
  • It is drier and less dense than the troposphere.
  • Temperature increase as altitude increase due to presence of the ozone layer which absorbs ultraviolet rays from the sun.
  • It plays the important role of absorbing ultraviolet radiations which otherwise reach the Earth’s surface.
  • The stable air of the stratosphere prevents large storms from extending much beyond the tropopause.
  • Planes fly in the stratosphere because it has strong steady horizontal winds, which are above the stormy weather of the troposphere.
NOTE:
The boundary which separates the stratosphere and the Mesosphere is called “stratosphere”

MESOSPHERE
The mesosphere starts just above the stratosphere and extends to 85km high.

PROPERTIES MESOSPHERE
  • The temperature decrease with the increase of altitude. The lowest temperature of atmosphere (-90°c) occur in this region.
  • It plays a great role in most meteors burn while entering the earth’s atmosphere.
NOTE:
The layer (boundary) which separates the Mesosphere and the thermosphere is called “Mesopause”

THERMOSPHERE
Is the layer starts just above the Mesosphere and extends up to 690km high.

PROPERTIES OF MESOSPHERE
  • The temperature increase as the increase of altitude due to the suns heat
  • The temperature can rise as high as 1720°C.
  • Chemical reactions occur much faster than on the Earth surface. It is sometimes called “upper atmosphere.
IONOSPHERE
Is the region (layer) containing a high concentration of charged particles called Ions and free- electrons.
The large number of free electrons allows the propagation of electromagnetic waves.

PROPERTIES OF IONOSSPHERE
  • It exists at the lower part of the thermosphere and upper part of Mesosphere. It extends from 80km to 530km above the Earth’s surface.
  • It plays an important role in absorption of dangerous radiations. The dangerous radiations include hard and support X – rays, and extreme ultraviolet (EUV).
  • Also plays important role in communications. Radio waves can be reflected off the ionosphere allowing radio communications over long distances.
EXOSPHERE
Is the outer most region of the atmosphere.

PROPERTIES OF EXOSPHERE
  • The atmospheric gas pressure is very low.
  • Light atoms such as hydrogen and Helium may acquire sufficient energy to escape the earth’s gravitation pull.
NOTE:
  • The upper part of the Exosphere is called (Magnetosphere(
  • This is the layer (region) where satellites orbit the Earth.
IMPORTANCE OF ATMOSPHERE
  • The troposphere controls the climate and ultimately determines the quality of life on the Earth.
  • The troposphere is important for life on the Earth. Contain gases such as oxygen and carbon dioxide for animal respiration and plant photosynthesis respectively. Also nitrogen which provide inactive environment for many chemical process to occur (Take place),
  • The stratosphere prevents harmful ultraviolet radiation from reaching the earth.
  • The mesosphere, thermosphere and exosphere prevent harmful radiation such cosmic rays from reaching the earth’s surface.
Ionosphere help in radio Communication


GLOBAL WARMING
Is the increase of the average temperatures near or on the surface of the earth as a result greenhouse effect.
GREENHOUSE EFFECT
Is the process in which the emission of radiation by the atmosphere warms the Earth’s surface.
The greenhouse gases are; carbon dioxide, Methane, Dinitrogen oxide, Chlorofloro carbons (CFC3)

GASES                                                                               
carbon dioxide

SOURCES                                     

  • Clearing and burning of vegetation
  • Burning of fossil fuels
GASES  
Methane

SOURCES                                             

  • Mining of coal and oil
  • Burning of vegetation
GASES  
Dinitrogen oxide 

SOURCES                                 

  • Combustion of fossil fuels in vehicles and power stations
  • Use of nitrogenous fertilizers
  • Burning of vegetation

GASES  
Chlorofloro carbons (CFC3)

SOURCES                     

  • Use of fridges and air conditioners

SOURCES OF GREENHOUSE EFFECT
  • Clearing and burning of vegetation.
  • Burning of fossil fuels.
  • Mining of coal and oil produce Methane.
  • The use of refrigerators and air conditioners.
EFFECTS OF GLOBAL WARMING
  • Increase of the temperature of the oceans.
  • Rise in sea levels.
  • Change in world’s climatic patterns.
  • Acidification of the oceans.
  • Extreme weather effects such as floods, droughts, heat waves and hurricanes.
  • Extinction of some animal and plant species.
SOLUTIONS TO GLOBAL WARMING
  • Put in place energy – conservation measure to reduce the use of fossil fuel such as the use of public transport, to minimize the number of vehicles.
  • The use of clean alternative sources of energy such as solar and wind.
  • To avoid deforestation and encourage reforestation that forest will absorb carbon dioxide.
CLASS ACTIVITY
(1)   (a) List down the various layers of the atmosphere starting from the earth’s surface.
       (b)Give one (1) importance of earth of the layers of the atmosphere.
      (c) What is the Ionosphere?
(2)   (a) What is global warming?
       (b)Name four gases that contribute to global warming and give one source of each.
       (c) Give four effects of global warming.
       (d) Explain three (3) measures that can be taken to control global warming.