Continent

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Continental Drift Theory by Alfred Wegener

Alfred Wegener's Continental Drift Theory, proposed in 1912, suggested that the Earth's continents were not always in their current positions but had moved over geological time. He theorised that around 200 million years ago, all the continents were joined together in a single massive supercontinent he named Pangaea (meaning "all lands"). This supercontinent was surrounded by a vast ocean called Panthalassa.
According to Wegener, Pangaea began to break apart, first into two large landmasses: Laurasia or Angaraland in the north (which would become North America, Europe, and Asia) and Gondwanaland in the south (which would become South America, Africa, Antarctica, India, and Australia). These smaller landmasses then continued to drift apart, eventually forming the continents as we know them today.
Book: Origin of Continent and Ocean.

Wegener gathered several lines of evidence to support his revolutionary idea:

Jigsaw Fit
Fossil Evidence
Rock and Mountain Formations
Paleoclimatic Evidence

Wegener presented compelling evidence for his theory, but it was initially met with scepticism due to his inability to explain how continents moved. He suggested forces like Earth's rotation and tidal effects, which were later deemed insufficient. It wasn't until the mid-20th century, with the development of Plate Tectonics explaining mantle convection and seafloor spreading, that Wegener's ideas were widely accepted and integrated into our understanding of Earth's dynamic surface.

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Theory of seafloor spreading

In 1960, Harry Hess proposed the theory of seafloor spreading. This theory explained how new oceanic crust is formed at mid-ocean ridges and then moves away from the ridges, carrying the continents with it.

Mid-ocean ridges: Hess suggested that molten material (magma) rises from the Earth's mantle along these underwater mountain ranges.
New crust formation: As this magma cools, it solidifies, creating new oceanic crust.
Spreading: This new crust then spreads outward from the ridge in both directions, like a conveyor belt.
Oceanic trenches: At deep oceanic trenches, the older, cooler, and denser oceanic crust eventually sinks back into the mantle, where it is recycled.

Seafloor spreading provided a crucial mechanism for Alfred Wegener's earlier idea of continental drift, explaining how continents could move over geological time.

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Theory of plate tectonics

In 1968, W. Jason Morgan made a pivotal contribution to the theory of plate tectonics with his paper, "Rises, Trenches, Great Faults, and Crustal Blocks." Building on Harry Hess's seafloor spreading concept, Morgan added mathematical rigour and a comprehensive framework to understand how the Earth's surface moves.

Rigid Plates: Morgan suggested that the Earth's lithosphere is made up of large, rigid "plates" that move together. This was significant because it revealed that both continents and ocean floors are part of these moving plates.
Spherical Geometry: He used Euler's theorem of rotation on a sphere to explain the movement of tectonic plates. This accounts for geological features like mid-ocean ridges (where plates separate), oceanic trenches (where plates collide and one sinks beneath the other), and transform faults (where plates slide past each other).
Unified Mechanism: Morgan's research linked seafloor spreading, continental drift, earthquakes, volcanoes, and mountain formation into a cohesive theory, showing that these phenomena result from the movement of rigid tectonic plates.

His model was a major advancement, turning the idea of continental drift into a mathematically supported theory and establishing the foundation for modern plate tectonics.

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Feature	Alfred Wegener (Continental Drift, 1912)	Harry Hess (Seafloor Spreading, 1960)	W. Jason Morgan (Plate Tectonics, 1968)
Core Idea	Continents were once a supercontinent (Pangaea) and drifted apart.	New oceanic crust is formed at mid-ocean ridges and spreads outwards.	Earth's lithosphere is divided into rigid plates that move relative to each other on the asthenosphere.
Mechanism	Proposed insufficient forces like "pole-fleeing" and tidal forces.	Proposed convection currents in the mantle as the driving force.	Provided the mathematical and geometrical framework for plate motion on a spherical Earth, incorporating seafloor spreading and subduction.
Focus	Movement of continents.	Creation and destruction of ocean floor.	Unified theory explaining the movement of both continents and ocean floors as part of rigid plates.
Key Evidence	Jigsaw fit of continents, matching fossils, rock types, paleoclimates across oceans.	Mid-ocean ridges, trenches, young age of ocean floor, thin sediment layer.	Magnetic anomalies (stripes) on the seafloor, distribution of earthquakes and volcanoes, transform faults.
Significance	First comprehensive hypothesis of moving continents, laying the groundwork.	Provided the crucial mechanism for continental movement and explained ocean floor features.	Synthesized previous ideas into a cohesive, widely accepted theory that explains most large-scale geological phenomena.

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Type of Plate movement

There are three main types of plate movements, defined by how the plates interact at their boundaries:

Feature	Divergent	Convergent	Transform
Movement	Plates move away from each other.	Plates move towards each other and collide.	Plates slide past each other horizontally.
Effect on Crust	New crust is created as magma rises and solidifies.	The crust is destroyed (subduction) or deformed/uplifted (collision).	Crust is neither created nor destroyed; it is conserved.
Typical Features	Mid-ocean ridges, rift valleys, and volcanic activity.	Ocean trenches, volcanic arcs (oceanic-oceanic or oceanic-continental), and mountain ranges (continental-continental collision).	Fault lines, frequent earthquakes.
Associated Hazards	Mild volcanic eruptions, shallow earthquakes.	Strong earthquakes, explosive volcanic eruptions, and tsunamis (in subduction zones).	Strong, shallow earthquakes; no significant volcanic activity.
Examples	Mid-Atlantic Ridge, East African Rift Valley.	Andes Mountains, Himalayas, Mariana Trench, Japan.	San Andreas Fault (California).
Mountains	Block Mountain	Folding Mountain	___

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One Liner

Ring of Fire length: 40,000 kilometres