Plate Tectonics and Continental Formation

Theory of Plate Tectonics and Formation of Continents

• Raisin Theory: Earth cooled after the Big Bang, causing it to contract like a grape turning into a raisin, leading to mountain formation and ocean basins.
• Theory of Isostasy: Earth's crust floats on the mantle, achieving equilibrium between buoyancy and gravity.
• Tectonic Processes: Result in the structure and properties of the Earth's crust; referred to as tectonic plates, which are massive slabs of rock.
• Abraham Ortelius (Theatrum Orbis Terrarum): Proposed that continents were once a single landmass, evidenced by fitting coastlines.
• Georges-Louis Leclerc (Count Buffon): Supported the idea that continents like Africa and South America were once connected.
• Francois Paget: Suggested an undivided continent existed before the Atlantic Ocean was formed due to sinking during Noah’s Flood.

Wegener’s Theory of Continental Drift

• Alfred Wegener (1915): Proposed that Pangaea existed during the Permian period, with earlier supercontinent Rodinia existing about 1.1 billion years ago.
• Continental Movements: Laurasia drifted southward, colliding with Gondwanaland around 514-425 million years ago, leading to the formation of Panthalassa.
• Pangaea Splitting: During the late Triassic period, Pangaea divided into Laurasia and Gondwanaland, moving to northern and southern poles, respectively.

Evidence of Plate Movement

• Fossil Similarities: Land reptiles' fossils, such as Lystrosaurus and Cynognathus, show striking resemblances across continents.
• Snider Pellegrini: Theorized a connected continent in the Pennsylvanian Period, disrupted by the "Great Flood."
• Eduard Suess: Argued that the fern Glossopteris's seed distribution supported the theory of continental drift.

Plate Boundaries

• Seafloor Spreading Theory (Harry Hess): Describes magma from volcanic activity creating new crust, resulting in ridges on the seafloor.
• Divergent Boundaries: Plates move apart, resulting in new seafloor formation as mantle material rises.
• Convergent Boundaries: Plates collide, leading to subduction where one plate moves beneath another, creating subduction zones and Wadati-Benioff zones.
  • Types of Convergent Boundaries:
    • Oceanic-Continental: Oceanic subducts under continental.
    • Oceanic-Oceanic: One oceanic plate subducts under another.
    • Continental-Continental: Plates collide to form mountains.
• Transform Boundaries: Plates slide past each other horizontally, e.g., San Andreas Fault.
• Rift Valleys: Formed at divergent boundaries through crustal extension.

Mantle Convection Theory

• Arthur Holmes (1929): Proposed that mantle movement pulls the lithosphere in a conveyor belt manner, driven by convection.
• Slab Pull Theory: Suggests that gravitational forces pull down older, denser slabs into the mantle.

Internal Structure of the Earth

• Crust: Outermost layer, about 1% of Earth, sits on the asthenosphere; Mohorovicic Discontinuity marks the boundary with the mantle.
• Mantle: Largest layer, made of molten rock, extends 2,900 km deep; divided into upper (660 km) and lower mantle.
• Outer Core: Liquid layer made of iron and nickel; responsible for Earth's magnetic field; temperature around 5,000°C.
• Inner Core: Solid, deepest layer at about 5,000°C to 6,000°C, thickness around 1,250 km.

Landforms

• Formation: Created by water, wind, ice, and tectonic forces; vary from rapid formation to millions of years.
• Types of Landforms: Mountain ranges, hills, plains, plateaus.

Aeolian Landforms

• Created by wind: Includes dunes, loess, and mushroom rocks.
  • Dunes: Sand mounds; shapes include crescent or parabolic.
  • Loess: Mineral-rich dust deposits.
  • Mushroom Rock: Eroded rock formations.

Erosional Landforms

• Created from erosion: Includes mesas, buttes, canyons, and gorges.
  • Mesas: Flat-topped mountains, surrounded by resistant rock.
  • Buttes: Smaller than mesas, formed by erosion.
  • Canyons/Gorges: Deep ravines carved by water or glaciers.

Mountainous and Glacial Landforms

• Volcanoes: Created through volcanic activity.
• Hills: Smaller than mountains, formed by faulting, typically under 300m tall.
• Valley/Dale: Low-lying areas formed by river or glacier actions.
• Glacial Landforms: Created by glaciers, include V-shaped (water) and U-shaped (glaciers) valleys.

Fluvial and Coastal Landforms

• Deltas: Formed where rivers meet oceans or estuaries; rich in alluvium, dating back around 7,000 years.