The_theory_of_plate_tectonics_without_qs

Introduction to Plate Tectonics

• The Theory of Plate Tectonics developed in the 1960s and 70s

  • Describes internal forces deforming the Earth’s crust.

Historical Background

• Alfred Wegener (1912) proposed the concept of a supercontinent.

  • All continents were once joined as Pangea, surrounded by a massive ocean.

  • Continental drift occurred leading to current landmasses:

    • Laurasia: North America, Europe, and most of Asia.

    • Gondwanaland: South America, Africa, India, Australia, and Antarctica.

Evidence Supporting Continental Drift

• Wegener's theory was based on several key observations:

  • Fossil Distribution: Same fossil species found on different continents.

  • Geological Similarities: Matching mountain trends and rock types found on separated continents (e.g., Scandinavia and Appalachian mountains).

  • Coastline Shapes: Shapes of Africa and South America fit together.

Sea-Floor Spreading

• Harry Hess (1960s) introduced the concept of sea-floor spreading.

  • Observations:

    • While mapping the sea floor during naval patrol, Hess noticed volcanic activities creating submarine mountain ridges.

    • Identified new crust formation through volcanic eruptions from the sea floor.

Evidence of Sea-Floor Spreading

• Research and drilling demonstrate the age differences in ocean floor rocks:

  • Oil reserves depleted on land prompted offshore exploration.

  • Deep sea samples showed rocks near South America and Africa edges up to 200 million years older than those at the Mid-Atlantic Ridge.

  • Rocks formed at the Mid-Atlantic Ridge were younger, confirming gradual formation and spreading.

  • Satellite measurements show that South America and Africa are moving apart at approximately 5 cm/year, solidifying proof of ocean floor spreading and continental drift.

Development of Plate Tectonic Theory

• Vine and Matthews integrated ideas from Wegener’s continental drift and Hess’s sea-floor spreading.

  • Mapped earthquakes and volcano distributions indicating the Earth's crust is segmented into plates.

  • Identified convection currents of molten magma in the mantle as the driving force behind plate movement.

Conclusion

• The Theory of Plate Tectonics unifies geological phenomena and explains the movement and interaction of tectonic plates.

• Essential for understanding earthquakes, volcanoes, and the geological history of our planet.