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Mechanical Layers

Mar 8, 2025

Mechanical Layers and Plate Tectonics

Introduction

  • Plate tectonics explains several geological phenomena:
    • Volcanism
    • Earthquakes
    • Mountain belts
    • Fossil and paleo-climate mysteries
  • Key question: What is a tectonic plate?

Tectonic Plate

  • Defined as a piece of Earth's rigid solid lithosphere.
    • Composed of crust + uppermost mantle.
  • There are 7 major and about 20 minor plates.
  • Plates move relative to one another atop the flowing asthenosphere.

Earth's Layers

Compositional Layers (Review)

  • Crust
    • Made of granite (continental) or basalt (oceanic)
  • Mantle
    • Composed of peridotite
  • Core
    • Consists of iron and nickel

Mechanical Layers

  • Lithosphere
    • Brittle solid, breaks under stress
  • Asthenosphere
    • Plastic solid, flows under stress
  • Mesosphere
    • More rigid than the asthenosphere but flows slowly
  • Outer Core
    • True liquid, flows
  • Inner Core
    • Solid, does not flow

Characteristics of Earth's Layers

  • Temperature increases toward the center of the Earth, increasing likelihood of melting.
  • Pressure increases toward the center, increasing likelihood of solidification.
  • Composition changes affect the state (solid, liquid) at various temperatures and pressures.

Focus of the Unit: Lithosphere and Asthenosphere

  • Lithosphere
    • Composed of the crust and upper mantle.
    • Rigid, brittle, behaves elastically (can snap).
  • Asthenosphere
    • Located directly below the lithosphere.
    • Behaves plastically (flows like ooblek, a non-Newtonian fluid).