Plate Tectonics and Continental Drift Theory

Historical Development of Plate Tectonics

• Early Earth scientists believed in catastrophism, which stated that present landscapes were created by sudden cataclysms
• Uniformitarianism, a contrasting concept, proposes that internal and external Earth processes occur gradually, not suddenly
• This paradigm shift occurred after 1830, rejecting catastrophism

Continental Drift Theory

• Alfred Wegener, a German climatologist, proposed Continental Drift in 1912
• The theory suggests that continents and landmasses have shifted positions over millions of years
• Pangaea, a single supercontinent, existed around 255 million years ago
• Pangaea Ultima (Neopangaea) formed around 250 million years ago

Evidence Supporting Continental Drift

• Continental Fit: Opposing coastlines of continents fit together
• Similarity of Mountain Ranges: Mountain ranges of the same age in adjoining locations on opposite continents match
• Similarity of Rock Sequences
• Paleoclimate Evidence: Glacial deposits formed 300 million years ago in India, Australia, South America, and Southern Africa match those found in Antarctica today
• Fossil Evidence: Fossils of species like Cynognathus, Mesosaurus, Lystrosaurus, and Glossopteris were found in different continents, supporting continental drift

Seafloor Spreading Theory

• Proposed by Harry Hess in 1960
• Sea floor moves outward from Mid-Oceanic Ridges

Theory of Plate Tectonics

• Involves the interaction of two layers: Lithosphere (outer layer of the mantle) and Asthenosphere (inner layer of the mantle)
• Lithosphere is a 100km thick shell of hard, strong rock that floats on the hot, plastic asthenosphere
• Plate Boundaries separate one plate from another, characterized as:
  • Divergent Boundaries: Moving away from each other
  • Convergent Boundaries: Moving towards each other
  • Transform Boundaries: Plates slide past one another

Laws of Geology

• Law of Original Horizontality: Rock layers are originally laid down horizontally and can later be deformed
• Law of Superposition: Oldest layer is at the base
• Principle of Cross-Cutting Relationships: Cuts or disrupts
• Idea of Unconformities: Continuous until they encounter other solid bodies

Dating Methods

• Relative Dating: Tells how old something is, but does not provide a specific year or date
• Absolute Dating: Provides a specific calendar year
• Radioactive Decay: Unstable atomic nucleus loses energy by emitting radiation
• Half-Life: Time needed for half of the sample of radioactive substance to undergo radioactive decay
• Radiometric Dating: Estimates how long ago rocks are formed

Geologic Time Scale

• Eon: Phanerozoic, Proterozoic, Archean, Hadean (derived from the Greek word "hades")
• Era
• Period
• Epoch

Learn about the concepts of plate tectonics, catastrophism, uniformitarianism, and the continental drift theory. Explore how Earth's surface has been shaped over millions of years through gradual processes and the movement of its segments.