Earth's Dynamic Interior: From Continental Drift to Plate Tectonics

Unveiling Earth's Inner Structure

Methods of Studying Earth's Interior

• Surveys and Mines: Limited to depths of approximately 13 km.
• Terrestrial Radio-Study: Provides insights into deeper structures.
• Natural Rocks: Phenomena like volcanic eruptions bring rocks formed in the Earth's interior to the surface.
• Meteorites: Offer information about the primordial materials of the solar system.
• Seismic Waves: Scientific methods based on the analysis of seismic waves produced by earthquakes, recorded by seismographs.

Seismic Waves: P-waves and S-waves

• P-waves (Primary Waves):
  • First to arrive and are major waves.
  • Faster in solids than in liquids.
  • Cause compression and decompression waves.
• S-waves (Secondary Waves):
  • Second to arrive and are smaller waves.
  • Only travel through solids.
  • Particles vibrate internally perpendicular to the wave direction.

Earth's Compositional and Dynamic Layers

The Earth's interior is distributed in layers:

• Compositional Layers: Characterized by increasing density and separated by seismic discontinuities.
• Dynamic Layers: The lithosphere is the rigid, shallow layer that encompasses the entire crust and a portion of the upper mantle.

The Theory of Continental Drift

Alfred Wegener's Revolutionary Hypothesis

Alfred Wegener was the first to gather evidence explaining the resemblance between continents. He demonstrated that the fit was much better when connecting the continents by their continental shelves rather than their present-day coasts. Both continents showed rocks of the same age and identical fossils.

Wegener presented a revolutionary hypothesis of mobility: continental drift. He proposed that approximately 200 million years ago, the continents had been united in a single supercontinent called Pangea. He supported his theory with paleontological, geological, and paleoclimatic evidence.

Understanding Plate Tectonics

Lithospheric Plates and Subduction

The lithosphere is divided into fragments called lithospheric plates, which are separated by seismic activity. In areas of subduction, the seafloor appears to bend and sink into the mantle.

Key Principles of Plate Tectonics

1. The lithosphere is divided into large blocks called plates.
2. Most internal geological activity is concentrated at the boundaries between these deep ocean plates.
3. New plate material is continuously generated at mid-ocean ridges and destroyed in oceanic trenches.
4. Plates interact with each other, causing continents to move and deform.

The Wilson Cycle of Supercontinents

Wegener did not suspect that continents held different positions before Pangea, or that Pangea itself was different at the beginning of the Primary Age. John Tuzo Wilson was the first to propose the existence of processes involving the breakup and reunification of supercontinents. This cyclical process is now known as the Wilson Cycle.