Origin and Structure of the Earth

• Origin and Structure of the Earth includes the Big Bang Theory, Earth's internal structure, minerals, and rocks.

Big Bang Theory

• The Big Bang Theory explains the universe's origin as a massive explosion.
• The Big Bang happened approximately 13.8 billion years ago.
• Georges Lemaitre, a Belgian priest and astronomer, proposed the Big Bang Theory in the 1920s.

Evidence Supporting the Big Bang

• Redshift of galaxies, discovered indicating the universe's expansion.
• Cosmic Microwave Background Radiation (CMBR), discovered being a remnant of the Big Bang.
• Gravitational waves, detected, further confirm early cosmic inflation.

Earth's Internal Structure

• The Earth is composed of four main layers.
• The crust is the outermost solid layer.
  • Continental crust is granite-based, thicker, and less dense.
  • Oceanic crust is basalt-based, thinner, and denser.
• The mantle is the thickest layer.
  • The mantle is composed of semi-solid rock (peridotite).
  • Convection currents in the mantle drive plate movements.
• The outer core is composed of liquid iron and nickel.
  • The outer core is responsible for Earth's magnetic field.
• The inner core is solid due to immense pressure.
  • The inner core is composed of iron and nickel.

Minerals and Rocks

• Mineral: Naturally occurring, inorganic, crystalline solid with a specific chemical composition.
• Rock: An aggregate of one or more minerals.
• Ore: A rock containing valuable minerals or metals that can be mined for profit.

Properties of Minerals

• Luster describes how a mineral reflects light (e.g., metallic, vitreous, pearly, dull).
• Color can be unreliable due to impurities.
• Streak refers to the color of the powdered mineral when scratched on a streak plate.
• Transparency indicates if minerals can be transparent, translucent, or opaque.
• Hardness is a physical property measured using the Mohs Scale of Hardness (1 = Talc, 10 = Diamond).
• Cleavage is the tendency of minerals to break along flat surfaces.
• Fracture is the way minerals break when no cleavage is present (e.g., conchoidal, uneven).
• Specific Gravity represents the density of a mineral compared to water.
• Tenacity indicates how a mineral resists breaking or deforming (e.g., brittle, elastic, malleable).

Types of Rocks

• Igneous Rocks form from cooling magma/lava.
  • Intrusive (Plutonic) rocks cool slowly beneath the surface (e.g., Granite, Diorite, Gabbro).
  • Extrusive (Volcanic) rocks cool rapidly on the surface (e.g., Basalt, Rhyolite, Obsidian, Pumice).
• Sedimentary Rocks form from compacted sediments.
  • Clastic rocks are made of weathered rock fragments (e.g., Sandstone, Shale, Conglomerate, Breccia).
  • Chemical rocks precipitate from mineral-rich water (e.g., Limestone, Rock Salt, Chert).
  • Organic rocks derive from biological remains (e.g., Coal, Chalk, Fossiliferous Limestone).
• Metamorphic Rocks are altered by heat and pressure.
  • Foliated rocks show layered texture (e.g., Schist, Gneiss, Slate).
  • Non-foliated rocks have no distinct layers (e.g., Marble, Quartzite, Anthracite coal).

Geological Processes include Exogenic and Endogenic Processes

• Exogenic Processes (External Forces)
  • Weathering involves the breakdown of rocks into smaller particles.
    • Mechanical Weathering: Physical forces break rocks apart (e.g., frost wedging, root wedging, abrasion, exfoliation).
    • Chemical Weathering: Chemical reactions alter minerals (e.g., oxidation, dissolution, hydrolysis).
  • Erosion is the removal of sediments by wind, water, glaciers, or gravity.
  • Deposition is the accumulation of sediments in a new location.
  • Deposition forms landforms such as deltas, beaches, and sand dunes.
• Endogenic Processes (Internal Forces)
  • Volcanism: The movement of magma to the surface, forming volcanoes and igneous rock formations.
  • Plate Tectonics: The movement of Earth's lithospheric plates.
    • Divergent Boundaries: Plates move apart (e.g., Mid-Atlantic Ridge, East African Rift).
    • Convergent Boundaries: Plates collide, forming mountains, subduction zones, and volcanic arcs (e.g., Himalayas, Ring of Fire).
    • Transform Boundaries: Plates slide past each other, causing earthquakes (e.g., San Andreas Fault).

Geological Time Scale

• Precambrian Supereon (4.6 billion – 541 million years ago): Formation of Earth, first life forms.
• Phanerozoic Eon (541 million years ago - present): Visible life forms.
• Paleozoic Era: Explosion of marine life, first land plants and animals.
• Mesozoic Era: Age of dinosaurs, first birds and mammals.
• Cenozoic Era: Age of mammals, human evolution.

Natural Hazards

• Earthquakes are caused by the release of energy along faults due to tectonic movements.
  • Measurement:
    • Richter Scale: Measures magnitude (energy released).
    • Moment Magnitude Scale (Mw): Preferred by scientists for accuracy.
    • Mercalli Intensity Scale: Measures effects on structures and people.
  • Effects:
    • Ground Shaking: Causes buildings to collapse.
    • Liquefaction: Saturated soil behaves like liquid.
    • Tsunamis: Large sea waves caused by undersea quakes.
    • Landslides: Triggered by seismic activity on unstable slopes.

Volcanic Eruptions

• Types of Volcanoes:
  • Shield Volcanoes: Gentle slopes, basaltic lava (e.g., Hawaii).
  • Stratovolcanoes: Explosive eruptions, andesitic lava (e.g., Mt. Fuji, Mt. St. Helens).
  • Cinder Cones: Small, steep slopes, pyroclastic material (e.g., Paricutin in Mexico).

Dating Techniques

• Relative Dating
  • Superposition: Oldest layers at the bottom, youngest at the top.
  • Cross-cutting Relationships: Faults and intrusions are younger than the layers they cut.
  • Inclusions: Rock fragments within another rock are older than the surrounding material.
• Absolute Dating
  • Carbon-14 Dating: Used for dating organic remains (up to 50,000 years old).
  • Potassium-Argon Dating: Used for dating volcanic rocks (millions of years old).
  • Uranium-Lead Dating: Used for very old rocks (billions of years old).

Key Terms

• Subduction: One plate sinking beneath another.
• Fossilization: Preservation of organisms in sedimentary rock.