Theory of Plate Tectonics Honors

Theory of Plate Tectonics

Overview of Continental Drift Theory

• Alfred Wegener: A meteorologist who proposed the Continental Drift Theory in 1912.

  • Suggested that continents are drifting on the ocean.

  • Theory was dismissed due to lack of explanation for how movement occurred.

  • His theory paved the way for the later development of the Theory of Plate Tectonics, about 50 years later.

Evidence Supporting Continental Drift Theory

1. Puzzle-like Fit of Continents

• Continents appear to fit together like pieces of a puzzle.

  • Wegener's reasoning: All continents were once joined as a single supercontinent called Pangea (meaning "all the earth").

2. Ancient Climate Similarities

• Similar climates on different continents do not match current climates.

  • Evidence includes:

    • Glacial grooves and rock deposits found near the equator.

    • Coral reefs and coal deposits (from ancient swamps) found in colder regions.

  • Wegener's reasoning: These regions must have shifted location over time.

3. Fossil Distribution

• Fossils of the same species are found in rocks of the same age across continents separated by oceans.

  • Evidence that:

    • Seeds of these plants were too heavy to be dispersed by wind.

    • Reptiles could not swim across vast oceans.

  • Wegener's reasoning: Organisms existed when continents were joined and became dispersed after they drifted apart.

4. Geological Structures

• Same geological features (rocks and mountains) found on different continents.

  • Example: Appalachian Mountains are similar to mountain ranges in Eastern Greenland, Ireland, Great Britain, and Norway.

  • Wegener's reasoning: A single mountain range once formed and separated as continents drifted apart.

The Development of the Theory of Plate Tectonics

• Derived from Continental Drift Theory in the 1960s.

  • Dr. Harry Hess discovered seafloor spreading, providing a model for how continents move.

• Key Components of the Theory:

  • The Earth's outer shell (lithosphere) is broken into tectonic plates.

  • These plates are in constant slow motion.

  • Movement is driven by processes such as ridge push and slab pull.

Mechanisms of Plate Motion

• Convection in the Mantle: Causes the movement of tectonic plates.

  • Ridge Push: Hotter magma rises from the lower mantle, pushing plates apart as it approaches the surface.

  • Slab Pull: Cooler magma sinks back toward the mantle, pulling the plates with it.

Evidence Supporting the Theory of Plate Tectonics

Magnetic Evidence

• Minerals in newly formed rocks point towards magnetic north.

  • The magnetic field reverses every 200,000-300,000 years, altering mineral polarity in the rocks as well.

Seafloor Mapping

• Hess used radar technology during WWII to analyze the ocean floor, discovering mid-ocean ridges.

  • He found that the youngest rocks are situated at mid-ocean ridges and the oldest rocks are further away.

  • Seafloor spreading creates new oceanic crust, contributing to the movement of continents due to ridge push.

Geological Timeline (Image Reference)

• Timeline includes geological eras from Quaternary to Permian, indicating the age of oceanic lithosphere.

  • Provides context for understanding plate tectonics over geological timescales.