SCIENCE

Continental Drift Theory

  • Definition: States that the continents were once joined together as a single supercontinent called Pangaea 300×106 years300×106years ago and have gradually moved to their present positions over millions of years.

  • Pangaea: Derived from the Greek words pan ("all") and gaia ("Earth"), meaning "all Earth."

  • Proposed By: Alfred Lothar Wegener, a German meteorologist, geophysicist, and polar researcher.

    • Published The Origin of Continents and Oceans in 1915, outlining his theory of Continental Drift.





Evidence of Continental Drift

  1. Continental Fit

    • Continents fit together like a giant jigsaw puzzle.

    • Examples:

      • Coastlines of South America and Africa

      • Alignment between India, Madagascar, and Africa

  2. Rocks and Mountain Correlation

    • Rocks in different continents share the same age, structure, and type.

    • Examples:

      • Appalachian Mountains (North America) and Scottish Highlands

      • Karoo system (South Africa) and Santa Catarina system (Brazil)

  3. Fossil Remains

    • Identical fossils of plants and animals found on continents separated by vast oceans.

    • Examples:

      • Mesosaurus: Freshwater reptile from the Permian Period (286−258 Ma286−258Ma), found in South Africa and South America.

      • Cynognathus: Land-dominant, mammal-like reptile from the Triassic Period (250−240 Ma250−240Ma), found in South Africa and South America.

      • Lystrosaurus: Mammal-like land reptile from the Late Permian Period (250 Ma250Ma), found in Africa, Antarctica, and India.

      • Glossopteris: Large seed-bearing plant/tree from the Permian Period (299 Ma299Ma), found in Australia, Antarctica, India, South Africa, and South America.

  4. Paleoclimatic Evidence

    • Evidence of past climates (palaios = ancient, klima = region) that no longer match current continental climates.

    • Examples:

      • Glacial Striations & Deposits: Glacial deposits and scratches found in modern tropical/temperate regions like India, South America, and Africa.

      • Coal Deposits: Remnants of tropical swamps found in Antarctica, indicating it was once located near the equator in a warmer climate.

Coal is classified into four main ranks (plus a precursor stage) based on the amount of carbon it contains and the amount of heat energy it can produce:

  1. Peat

    • Description: A precursor to coal formed from partially decayed organic matter and vegetation in wet environments (bogs/swamps).

    • Properties: High moisture content and low carbon content (<60%<60%). Produces low heat energy and high amounts of smoke when burned.

  2. Lignite (Brown Coal)

    • Description: The lowest rank of true coal, formed when peat is subjected to increased pressure and heat over millions of years.

    • Properties: Carbon content of 60%−70%60%−70%. High moisture content, crumbly texture, and relatively low heat output. Used mainly for electricity generation.

  3. Sub-Bituminous Coal

    • Description: An intermediate rank between lignite and bituminous coal.

    • Properties: Carbon content of 70%−80%70%−80%. Lower moisture content than lignite and higher heating value. Primarily burned for electric power generation.

  4. Bituminous Coal (Soft Coal)

    • Description: The most abundant and widely used type of coal worldwide.

    • Properties: Carbon content of 80%−86%80%−86%. High energy density and lower moisture content. Commonly used in electricity production and refined into coke for steel manufacturing.

  5. Anthracite (Hard Coal)

    • Continental Drift Theory Overview

      • Definition: States that the continents were once joined together as a single supercontinent called Pangaea 300×106 years300×106years ago and have gradually moved to their present positions over millions of years.

      • Pangaea: Derived from the Greek words pan ("all") and gaia ("Earth"), meaning "all Earth."

      • Proposed By: Alfred Lothar Wegener, a German meteorologist, geophysicist, and polar researcher.

        • Published The Origin of Continents and Oceans in 1915, outlining his theory of Continental Drift.





Unit 3: Earth and Its Processes


Familiarizing Earth's Interior & Layers

  • Main Layers:

    • Crust: Oceanic Crust, Continental Crust

    • Mantle: Upper Mantle (including Lithosphere & Asthenosphere), Lower Mantle

    • Core: Outer Core, Inner Core

Two Types of Lithospheric Crust

  • Continental Crust:

    • Relative Age: Older

    • Relative Thickness: Thicker

    • Relative Density: Less dense

    • Type of Rock: Granitic / Granite

  • Oceanic Crust:

    • Relative Age: Younger

    • Relative Thickness: Thinner

    • Relative Density: Denser

    • Type of Rock: Basaltic / Basalt

Plate Tectonics Theory

  • Definition: Suggests that Earth's lithosphere is divided into large, rigid plates that slowly move over the semi-fluid asthenosphere.

Earth's Primary Plates

  • Pacific Plate

  • North American Plate

  • Eurasian Plate

  • African Plate

  • Antarctic Plate

  • Australian Plate

  • South American Plate

Earth's Secondary Plates

  • Juan de Fuca Plate

  • Nazca Plate

  • Cocos Plate

  • Caribbean Plate

  • Philippine Plate

  • Arabian Plate

  • Indian Plate

  • Scotia Plate

Mechanisms of Tectonic Movement

  1. Mantle Convective/Convection Theory

    • Proposed By: Arthur Holmes (1928−19291928−1929)

    • Description: Suggests that heat from Earth's interior causes hot mantle material to rise and cooler material to sink, creating convection currents.

    • Role: Primary driving force of plate movement.

  2. Slab Pull Theory

    • Description: The idea that a cold, dense oceanic plate sinks into the mantle at a subduction zone, pulling the rest of the tectonic plate along with it.

    • Subduction: Process in which one tectonic plate is forced beneath another plate and sinks into the Earth's mantle.

    • Role: Dominant driving force of plate movement.

Evidence of Plate Tectonics Theory

  1. Seafloor Spreading

    • Proposed By: Harry Hess (1960−19621960−1962)

    • Description: Process by which new oceanic crust forms at mid-ocean ridges and moves away from the ridge.

    • Mid-Ocean Ridge: A long chain of underwater mountains where two tectonic plates move apart (hot magma rises, cools down, forming new oceanic floor).

  2. Magnetic Stripes on the Seafloor

    • Description: Magnetic stripes are patterns of normal and reversed polarity in the oceanic crust.

    • Geomagnetic Reversal: The periodic change in Earth's magnetic field, when magnetic north and south poles switch places.

  3. Age of Oceanic Crust

    • Description: Oceanic crust is younger near mid-ocean ridges and becomes progressively older farther away, providing evidence that new crust forms through seafloor spreading.

  4. Distribution of Earthquakes and Volcanoes

    • Description: The distribution of earthquakes and volcanoes shows where tectonic plates interact and move against, apart, or beneath one another.





Types of Plate Boundaries

  • Definition: Plate boundaries are the edges where two tectonic plates meet. Their interaction shapes Earth's surface and forms landforms like mountains, volcanoes, ocean trenches, and faults.

1. Convergent Plate Boundaries (Destructive Boundaries)

  • Definition: Boundaries where two tectonic plates move toward each other.

  • Why Destructive: Crust is destroyed when one plate is forced beneath another into the mantle via subduction.

  • Major Landforms: Mountains, volcanoes, and ocean trenches.

  • Subtypes & Examples:

    • Oceanic-Continental Convergence (O-C):

    • Andes Mountains (South America): Formed by Nazca Plate subducting under South American Plate.

    • Cascade Range (North America): Formed by Juan de Fuca Plate subducting under North American Plate.

    • Oceanic-Oceanic Convergence (O-O):

    • Mariana Trench (Western Pacific): Formed by Pacific Plate subducting under Philippine Plate.

    • Aleutian Islands (Alaska, USA): Formed by Pacific Plate subducting under North American Plate.

    • Continental-Continental Convergence (C-C):

    • Himalayan Range (South-Central Asia): Formed by Indian Plate colliding with Eurasian Plate.

    • The Alps (Europe): Formed by African Plate colliding with Eurasian Plate.

2. Divergent Plate Boundaries (Constructive Boundaries)

  • Definition: Boundaries where two tectonic plates move away from each other.

  • Why Constructive: New crust is created as magma rises from the mantle and solidifies between separating plates.

  • Major Landforms: Mid-ocean ridges and rift valleys.

  • Subtypes & Examples:

    • Oceanic-Oceanic Divergence (O-O):

    • Mid-Atlantic Ridge (Atlantic Ocean): Formed by separation of North/South American Plates from Eurasian/African Plates.

    • East Pacific Rise (Pacific Ocean): Fast-spreading ridge between Pacific Plate and Nazca/Cocos Plates.

    • Continental-Continental Divergence (C-C):

    • African Rift Valleys (Africa): Formed by splitting of African Plate into Nubian and Somali Plates.

    • Baikal Rift (Siberia): Formed by pulling apart of Eurasian Plate, forming Lake Baikal.

    • Transition to New Ocean (Mature Rifting):

    • Red Sea (Middle East): Narrow ocean formed by separation of African and Arabian Plates.

    • Gulf of California.

3. Transform Fault Boundaries (Conservative Boundaries)

  • Definition: Boundaries where two tectonic plates slide past each other horizontally.

  • Why Conservative: Crust is neither created nor destroyed; stress accumulates and releases as earthquakes.

  • Major Landforms: Fault lines.

  • Examples:

    • San Andreas Fault (California, USA)