TJ

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.