Plate Tectonics Earths Layers Earths Plates and Continental Drift 2nd half

Changes in Earth's Surface

  • Changes in the earth’s surface occur slowly and often go unnoticed by the human eye.

  • The movement of the earth's landmasses is explained by the Plate Tectonic Theory.

Plate Tectonic Theory

  • Discovered about forty years ago by scientists studying the seafloor.

  • The ocean floor features tall mountains and deep trenches; a continuous mountain chain circles the Earth.

  • A deep crack in the seafloor signifies that it is pulling apart, causing tectonic plates to move in opposite directions, carrying continents and oceans with them.

  • Tectonic plates are the segments of Earth's top layer, constantly moving at speeds similar to nail growth.

  • Earth’s surface is divided into nine major and several smaller tectonic plates.

Earth’s Crust and Tectonic Plates

  • Earth's outer shell is not a single mass but consists of several moving plates.

  • These plates vary in size and thickness and float on a soft, malleable layer of the mantle.

Major Tectonic Plates

  • North American Plate: Extends from the mid-Atlantic Ocean to Japan.

  • Cocos Plate: Small plate in the Pacific Ocean west of Central America.

  • Tectonic plates slide over a hot and flexible mantle, not anchored in place.

Key Concepts in Plate Tectonics

  • Understanding Continental Drift and Seafloor Spreading is vital to comprehend the current layout of the earth.

Historical Perspectives on Continents

  • In the past, many scientists believed continents were static and unchanged.

  • Observations showed that South America and Africa could fit together, suggesting a historical connection.

  • Students are encouraged to create a model joining the continents to visualize this theory.

Continental Drift Theory

  • Proposed by a German scientist in the early 1900s, suggesting a once existing supercontinent called Pangaea.

Timeline of Pangaea’s Breakup

  • Wegner's Theory (180 million years ago): Pangaea began to fracture into separate continents.

  • Similar fossil evidence found in South America, Africa, India, and Australia supports this theory.

Seafloor Spreading Evidence

  • Study of the ocean floor revealed that rocks near underwater ridge systems are younger than continental rocks.

  • The underwater ridge acts as a source of upwelling molten rock, creating new oceanic crust through a process called seafloor spreading.

Future of Plate Movements

  • The potential for a new supercontinent in 250 million years is a topic of study and speculation.

How Tectonic Processes Shape Landscapes

  • Tectonic plates are continuously moving, causing geological phenomena:

    • Diverging Boundaries: Plates pull apart, creating features like rift valleys (e.g., Thingvellir in Iceland).

    • Converging Boundaries: Plates collide, with effects depending on their types:

      • Continental plates create mountain ranges (e.g., Himalayas formed from Indo-Australian and Eurasian collision).

      • Oceanic plates may form island groups when one slides beneath another.

    • Transform Boundaries: Plates slide past each other causing faults and earthquakes (e.g., San Andreas Fault in California).

Summary of Geological Processes

  • Diverging: Plates move apart, leading to volcanic activity and rift valleys.

  • Converging: Plates collide. Oceanic plates subduct, causing volcanic activity; continental plates create mountains.

  • Transforming: Plates slide past each other, causing earthquakes.

Geological Hazards from Plate Movements

  • Areas with active tectonic boundaries are prone to rift valleys, earthquakes, and volcanic eruptions, significantly impacting human environments.