Grade 8 Social Studies Complete Study Notes

Forces Shaping the Earth’s Surface

• Internal (Tectonic) Forces: These forces originate from inside the Earth and create the primary undulations of the crust. Major processes include:

  • Folding: The bending of rock layers due to pressure from one or two sides, most visible in sedimentary rocks.

  • Monocline: All rock layers bend in the same direction.

  • Anticline: Upward-bending rock layers.

  • Syncline: Downward-bending rock layers.

  • Fold Mountains: Formed by uplifted and folded crust due to compressional forces, typically at continent edges. Notable examples include:

    1. Andes (South America)

    2. Rockies (North America)

    3. Alps (Europe)

    4. Himalayas (Asia)

    5. Atlas (North Africa)

    6. Cape Ranges (South Africa)

    7. Australian Alps (Australia)

  • Faulting: Cracks formed in the Earth's crust due to tensional or compressional forces.

    • Normal Fault: Caused by tensional forces.

    • Reverse Fault: Caused by compressional forces.

    • Rift Valleys: Formed when land between parallel faults sinks. The East African Rift Valley is the largest, extending $7200\,km$ from Syria to Mozambique ($5600\,km$ within Africa).

    • Block (Horst) Mountains: Formed by the uplift of land between parallel faults.

  • Volcanism: The process where molten rock (magma) is forced to the surface, becoming lava.

    • Extrusive Landforms: Volcanoes, craters (top holes), calderas (wide craters), and Crater Lakes (e.g., Mount Zequala).

    • Intrusive Landforms: Solidified magma within the crust, including Batholiths (large masses), Laccoliths (mushroom-shaped), Dykes (vertical), and Sills (horizontal).

    • Types of Volcanoes:

      • Active: Recent eruptions (e.g., Erta'li, Fentale, Dubbi).

      • Dormant: Long inactivity but may erupt (e.g., Tatali, Dabbahu).

      • Extinct: Not expected to erupt (e.g., Mt. Ras Dejen, Mt. Batu).

  • Earthquakes: Sudden crust movements associated with faults.

    • Focus: Origin point deep inside Earth.

    • Epicenter: Point on the surface directly above the focus.

    • Measurement: Seismometer (instrument), Seismograph (record), and Richter scale ($0$ to $9$ magnitude).

    • Ring of Fire: Circum-Pacific Belt containing $75\%$ of volcanoes and $90\%$ of earthquakes.

• External (Gradational) Forces: Forces acting from outside to level the Earth’s surface.

  • Denudation: Lowering the land via Weathering (breaking rocks) and Erosion (moving particles).

    • Physical Weathering: Exfoliation (caused by temperature change), Frost action (freezing water in cracks), and Biological action.

    • Chemical Weathering: Rain action (forming carbonic acid to dissolve limestone into caves), creating Stalactites (roof), Stalagmites (floor), and Pillars.

  • Erosion Agents:

    • Running Water: Sheet (wide flow), Rill (small channels), and Gully (deep gorges) erosion.

    • Wind (Desert): Creates Sand dunes, Barchans (crescent-shaped), and Loess deposits.

Composition and Structures of the Earth’s Atmosphere

• Aerosols: Collective name for gases, dust, and moisture droplets in the atmosphere.

• Gas Composition:

  • Nitrogen: $78\%$ (most abundant).

  • Oxygen: $21\%$ (essential for life).

  • Trace/Minor Gases: Argon, Carbon Dioxide, etc.

• Atmospheric Layers (by temperature variation):

  1. Troposphere: $0\,km$ to $8/16\,km$. Contains $3/4$ of atmospheric mass; where weather occurs. Top boundary is the Tropopause.

  2. Stratosphere: Up to $50\,km$. Contains high Ozone concentration (absorbs UV radiation). Top is the Stratopause.

  3. Mesosphere: Up to $80/85\,km$. Coldest layer ($-100^{\circ}C$). Meteorites burn here. Top is the Mesopause.

  4. Thermosphere: Up to $1000\,km$. Separated into:

     • Ionosphere: Electrically charged particles for radio communication.

     • Exosphere: Outer fringe with hydrogen and helium.

Elements and Controls of Weather and Climate

• Weather vs. Climate: Weather is short-term (daily); Climate is the $30$-year average of weather conditions.

• Temperature Transfer: Conducted via Radiation (waves), Conduction (contact), and Convection (density differences).

• The Hydrological Cycle: Driven by solar energy. Key processes:

  • Evapotranspiration: Combined loss from water (evaporation) and plants (transpiration).

  • Condensation: Vapour to liquid.

  • Sublimation: Ice to vapour.

  • Deposition: Vapour to ice.

• Rainfall Types: Relief (Orographic), Convectional, and Frontal (Cyclonic).

• Atmospheric Pressure: Measured by barometers. Standard is $1013\,mb$ ($760\,mm$) at sea level. Decreases with altitude and temperature.

• Wind: Measured by anemometer (speed) and wind vane (direction).

• Climatic Controls:

  • Latitude: Distance from equator; affects solar intensity. Sun is overhead at tropics during Solstices (June 21, Dec 21) and the Equator during Equinoxes (March 21, Sept 23).

  • Altitude: Normal Lapse Rate is $6.4^{\circ}C$ per $1000\,m$.

  • Distance from Sea: Coastal areas are wetter and cooler.

  • Ocean Currents: Can be Warm or Cold.

• Ethiopia’s Agro-climatic Zones:

  1. Wurch (Alpine): >3300\,m, <10^{\circ}C.

  2. Dega (Temperate): $2300-3300\,m$, $10-15^{\circ}C$.

  3. Woina Dega (Sub-tropical): $1500-2300\,m$, $15-20^{\circ}C$.

  4. Qolla (Tropical): $500-1500\,m$, $20-30^{\circ}C$.

  5. Bereha (Desert): <500\,m, >30^{\circ}C.

People and Socioeconomic Activities

• Culture:

  • Material: Artifacts like tools, clothing, houses.

  • Non-material: Values, beliefs, symbols, language.

  • Ethiopian Language Families:

    1. Semitic: Amharic, Ge’ez, Tigrigna, Guragigna.

    2. Cushitic: Afan Oromo, Sidamigna, Somaligna, Afarigna.

    3. Omotic: Welaytta, Gamo-Gofa.

    4. Nilo-Saharan: Agnuak, Berta, Gumuz.

• Economic Activities:

  1. Primary: Extraction (Agriculture, Forestry, Fishing, Mining).

  2. Secondary: Value-added (Manufacturing, Construction, Power).

  3. Tertiary: Services (Transport, Communication, Tourism, Health).

• Market Forces:

  • Demand: Quantity buyers are willing to purchase.

  • Supply: Quantity sellers are willing to sell.

  • Market Equilibrium: Intersection of supply and demand curves.

  • Perfect Competition: Many buyers/sellers, uniform products, price-takers.

• Government Revenue and Tax: Mandated charges to fund public works.

  • Historical Tax in Ethiopia: First system under King Zerayacob ($1434-1468$); Tithe reforms under Menelik II.

  • Derg Regime Tax: Proclamations $77/1976$ and $152/1978$ (Agri-producers paid $5\text{ birr}$, individual peasants $10\text{ birr}$).

Natural Resources and Development

• Resource Types:

  • Renewable: Generates again (sun, soil, plants).

  • Non-renewable: Exhaustible (oil, coal, minerals).

• Conservation Methods:

  • Soil: Terracing (Konso Cultural Landscape is a UNESCO site), Afforestation, Strip cropping, Crop rotation, Contour ploughing.

  • Water: Pollution protection, rational groundwater use, industrial water reuse.

• Hydro-politics of Abay (Nile): Conflict between upper course (contributing water) and lower course (benefit recipients like Egypt and Sudan) countries.

World History

• Geographical Discoveries:

  • Motives: Trade, interest in Far East, scientific progress.

  • Discoverers:

    • Bartholomew Diaz: Reached "Cape of Storms" (Cape of Good Hope) in $1488$.

    • Vasco da Gama: Reached India in $1498$.

    • Christopher Columbus: Reached Bahamas in $1492$.

    • Ferdinand Magellan: First circumnavigation ($1519-1522$).

• Renaissance & Reformation:

  • Renaissance: Rebirth of Greco-Roman culture in Italy. Icons: Gutenberg (Printing press $1450$), Da Vinci (Mona Lisa), Michelangelo (Sistine Chapel), Copernicus (Heliocentric theory).

  • Reformation: Martin Luther launched Protestantism in $1517$ via Ninety-Five Theses.

  • Counter-Reformation: Jesuits (Ignatius Loyola) and Council of Trent ($1545-1563$).

• Industrial Revolution: Shift from human labor to machines.

  • 1st Stage ($1750-1870$): Steam power, iron, coal.

  • 2nd Stage ($1870\text{-present}$): Electricity, petroleum, atomic energy, computers.

• World Wars:

  • WWI ($1914-1918$): Triple Alliance (Germany, Austria-Hungary, Italy) vs. Triple Entente (Britain, France, Russia). Trigger: Assassination of Archduke Franz Ferdinand. Ended by Treaty of Versailles ($1919$).

  • WWII ($1939-1945$): Axis (Germany, Italy, Japan) vs. Allies (Britain, France, Russia, USA). Trigger: Invasion of Poland. Atomic bombs dropped on Hiroshima and Nagasaki.

• Cold War ($1945-1991$): Ideological struggle between Capitalist (USA) and Communist (USSR) blocs. Ended under Mikhail Gorbachev (Glasnost).

Africa and Ethiopia Since 1500s

• Slavery: The Trans-Atlantic Slave Trade used Africans for plantations in the New World. Triangular Trade linked Europe (goods), Africa (slaves), and Americas (raw materials). Abolished in British colonies ($1834$).

• Colonialism: Berlin Conference ($1884-1885$) partitioned Africa. Ethiopia and Liberia remained independent.

• Modern Ethiopia:

  • Emperors: Tewodros II (unity), Yohannes IV (diplomacy/battles with Egypt: Gundat, Gura), Menelik II (Adwa victory vs. Italy in $1896$), Haile Selassie I (league of nations, modern administration).

  • Fascist Italian Occupation ($1936-1941$): Triggered by Wal Wal incident ($1934$). Ended with British support in $1941$.

  • Somalia Aggression ($1977$): Siyad Barre's attempt to take Ogaden was defeated at the Battle of Kara Mara by Ethiopia with help from USSR and Cuba.

Contemporary Global Issues

• Climate Change: Long-term global shifts largely due to $CO_2$ from fossil fuels.

  • Greenhouse Effect: Trapping heat via gases like Methane ($CH_4$), $CFCs$, and Nitrous Oxide ($N_2O$).

  • Air Pollution: Responsible materials like Carbon Monoxide ($CO$) and Sulphur Dioxide ($SO_2$).

  • Ethiopia's Strategy: Climate-Resilience Green Economy (CRGE) aimed at middle-income status by $2025$.