PANTOMATH

Physical Geology 1. Earth’s Internal Structure and Composition

The Earth is made up of three main layers:

• Crust: The outermost layer, divided into continental crust (thicker, less dense, mostly granite) and oceanic crust (thinner, denser, mostly basalt).
• Mantle: A thick layer beneath the crust, made of semi-solid rock that moves slowly due to convection currents. It is divided into the upper mantle (asthenosphere) and lower mantle (mesosphere).
• Core: The innermost layer, composed of iron and nickel. It has two parts:
  • Outer Core – Liquid and responsible for Earth's magnetic field.
  • Inner Core – Solid due to immense pressure, despite extremely high temperatures.

Key Points:

• The Mohorovičić discontinuity (Moho) separates the crust from the mantle.
• The Lehmann discontinuity separates the inner and outer core.

2. Plate Tectonics and Continental Drift Theory

Continental Drift Theory
Proposed by Alfred Wegener (1912), this theory suggests that continents were once part of a supercontinent called Pangaea and later drifted apart.Evidence for Continental Drift:

Fossil similarities across continents (e.g., Mesosaurus in Africa and South America).
Matching rock formations on different continents.
Paleoclimatic evidence (glacial deposits in warm regions).
Plate Tectonics Theory
Expands on Wegener’s idea, stating that the Earth's lithosphere is broken into tectonic plates that move due to convection currents in the mantle.

Types of Plate Boundaries:

• Divergent Boundary (Constructive) – Plates move apart (e.g., Mid-Atlantic Ridge).
• Convergent Boundary (Destructive) – Plates collide, forming mountains or subduction zones (e.g., Himalayas, Andes).
• Transform Boundary (Conservative) – Plates slide past each other, causing earthquakes (e.g., San Andreas Fault).

Key Points:

The Ring of Fire is a zone of frequent earthquakes and volcanic eruptions due to active plate boundaries.
Seafloor spreading at mid-ocean ridges supports plate tectonics.

3. Types of Rocks and the Rock Cycle

Rocks are classified into three main types:

• Igneous Rocks (Formed from Cooling of Magma/Lava)
  • Intrusive (Plutonic): Formed inside the Earth (e.g., Granite).
  • Extrusive (Volcanic): Formed on the surface (e.g., Basalt, Pumice).
• Sedimentary Rocks (Formed by Deposition and Compaction of Sediments)
  • Clastic: Made of rock fragments (e.g., Sandstone).
  • Chemical: Formed by precipitation (e.g., Limestone).
  • Organic: Contain fossils or organic material (e.g., Coal).
• Metamorphic Rocks (Formed by Heat and Pressure on Existing Rocks)
  • Foliated: Layered appearance (e.g., Slate, Schist).
  • Non-Foliated: No layers (e.g., Marble, Quartzite).

The Rock Cycle:

• Rocks undergo transformation due to geological processes:
• Igneous rocks → Weathering → Sediments → Lithification → Sedimentary rocks
• Sedimentary rocks → Heat & Pressure → Metamorphic rocks
• Metamorphic rocks → Melting → Magma → Cooling → Igneous rocks

Key Points:

• Magma cools to form igneous rocks.
• Erosion and deposition form sedimentary rocks.
• Heat & pressure cause metamorphism.

4. Geological Processes: Weathering, Erosion, and Deposition

Weathering (Breakdown of Rocks in Place)

• Physical (Mechanical) Weathering:
  • Frost action (freeze-thaw cycles).
  • Exfoliation (peeling of rock layers due to temperature changes).
  • Biological activity (roots breaking rocks).
• Chemical Weathering:
  • Oxidation (e.g., rust formation).
  • Carbonation (dissolution of limestone by acidic rainwater).
  • Hydrolysis (reaction with water, e.g., feldspar turning into clay).

Erosion (Movement of Weathered Materials)

• Agents of erosion: Wind, water, ice, and gravity.
• Examples: River erosion forms valleys; glaciers carve U-shaped valleys.

Deposition (Settling of Eroded Material)

• Rivers deposit sediment to form deltas (e.g., Ganges Delta).
• Wind deposits sand to form dunes.

Key Points:

• Weathering weakens rocks; erosion transports materials; deposition builds new landforms.
• Karst landscapes (caves, sinkholes) form due to chemical weathering.

5. Natural Disasters: Earthquakes, Volcanoes, Tsunamis, and Landslides

Earthquakes (Sudden Shaking of the Earth’s Surface)

• Caused by movement along faults (e.g., San Andreas Fault).
• Focus (Hypocenter): The underground origin of the quake.
• Epicenter: The point directly above the focus on the surface.
• Measured using the Richter Scale and Seismographs.

Effects: Ground shaking, building collapse, landslides, tsunamis.

Volcanoes (Eruptions of Magma, Gas, and Ash)

• Formed at subduction zones, mid-ocean ridges, or hotspots.
• Types of volcanoes:
• Shield Volcanoes – Gentle eruptions, runny lava (e.g., Mauna Loa, Hawaii).
• Composite Volcanoes – Explosive eruptions, thick lava (e.g., Mount St. Helens).
• Cinder Cone Volcanoes – Small, steep slopes, single vent (e.g., Paricutin, Mexico).

Effects: Lava flows, ash clouds, pyroclastic flows, climate impact.

Tsunamis (Large Ocean Waves Caused by Underwater Disturbances)

• Triggered by earthquakes, volcanic eruptions, or landslides.
• Travel at high speeds across oceans; waves grow taller near shores.
• Example: 2004 Indian Ocean Tsunami (caused by a 9.1 magnitude earthquake).

Effects: Flooding, destruction, loss of life, coastal erosion.

Landslides (Rapid Movement of Rock, Soil, and Debris Down a Slope)

• Caused by heavy rain, earthquakes, deforestation, or human activities.
• Types:
• Rockfalls: Sudden breaking of rock.
• Slumps: Rotational movement of land.
• Mudflows: Fast-moving wet debris (common in hilly areas).

Effects: Property damage, road blockages, loss of life.