Fundamental Principles for Understanding Earth History

    Earth System Components

The Principle Of Uniformitarianism  "The present is the key to the past"

    Earth’s Basic Structure

  • internal layers
  • rocks and minerals

    Plate Tectonics

The Principle Of Uniformitarianism: "The present is the key to the past"

    Modern scientists believe that the physical laws of nature have not changed over the course of time. Therefore, processes we observe today can be applied to events of the past or even the future.

    Modern Alaskan glacier and glacial deposits in Ohio

Earth’s Internal Structure

  • Crust: Outermost layer; dense oceanic crust, less dense continental crust
  • Mantle: upper portion combined with the crust forms the Lithosphere which lays below a partially molten (melted rock = magma) layer called asthenosphere. The lithosphere is broken into segments or plates.
  • Core: liquid outer core, and solid inner core


Modern tectonic plates:  Note the location of numerous volcanoes. Earthquakes are also found concentrated at these boundaries.

Plate Tectonics = Process by which lithospheric plates move.

    Rising heat produce convection currents that converge driving plates together. Where convection currents diverge, this pushes the plates apart.

Types Plate Boundaries

    Convergent plate boundaries: See examples below

  • Continent crust - continent crust
  • Continent crust - oceanic crust
  • Oceanic crust - oceanic crust

Convergent Plate Boundaries: Subduction Zones

    A process called subduction drives one plate into the mantle. Melting occurs generating magma which buoyantly rises forming volcanoes. In the case of continent – continent collision the crust is thickened, major mountain building occurs.


Convergent Plates: Ocean - Ocean Collision

Features: a subducted slab, deep ocean trench, Island Arc Volcanism

Pacific Plate and Eurasian Plate forming the Japanese Islands

Convergent Plates: Ocean-Continent Collision

Features:  a subducting slab, deep ocean trench (close to the coast), Volcanic Mountains form with the continental plate:

  • Juan DeFuca & N. American Plate Cascade Range of the Pacific Northwest US

  • Nazca Plate & South American Plate  form the Andes Mountains

Convergent Plates: Continent-Continent Collision

    Crust thickens, extensive faulting occurs that regional uplifting and mountain building

  • Indian Plate colliding with Eurasian Plate forming The Himalayan Mountains

Divergent plate boundaries

  • Mid-ocean ridges
  • Mid-continent rifts

Divergent Plates: Mid-ocean Ridge

  • New crust is formed along a mid-ocean ridge & Transform faults also are found along the ridge.
  • Radiometric age dating shows progressively older rocks away from the ridge.

Divergent Plates: form with continents are called Continental Rifts

Transform Fault Boundaries

Summary of Tectonic Boundaries

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