Tectonic Plates Theory

Tectonics - movement of the Earth’s lithosphere (crust + upper mantle)

  • Made up of the lithosphere (rigid part of Earth and uppermost)

Plate Tectonics - movement of discrete segments of Earth’s lithosphere in relation to one another

  • Earth is divided into more than a dozen of different plates that move constantly and end up fitting like a puzzle

  • Meet at plate boundaries and move relative to one another

  • Earthquakes, volcanism, or mountain building are from tectonic activity

  • Magma forms to fill the gaps of the tectonic plates that move apart when it shoots through


Why are Plates Moving?

Mantle Convection

Convection of the Earth’s mantle raises hot rocks beneath mid ocean ridges (gaps). These rocks spread laterally (dragging the lithosphere above), cool, and sink back into the interior of the mantle.


Volcanoes

As lava comes up from the ground, the plate is moving and it forms volcanoes. Volcanoes can go off multiple times in thousands or millions of years because the plates move and get the hotspot multiple times

Age of Seafloor

  • As the crust moves away from the ridge crest (cracks/boundaries of tectonic plates) they get older and the closer the younger


Deep Sea Trenches

  • Formed when one plate is moving downwards


Boundaries


Active Boundary: Intersection of boundaries and/or activity

Passive Boundary: No intersection of boundaries or activity


3 Types of Boundaries

Divergent - Plates move apart

  • Hot material wells up

  • Small lens of melt at surface

  • Tension causes faulting and cracking

Convergent - Plates move together

  • Collide with one another

  • Stress

  • Mountain building and/or volcanism occurs

  • Subduction: where one plate is forced beneath another

Transverse/Transform- Plates slide past each other


Could be continent-continent, continent-oceanic, or oceanic-oceanic boundaries

For oceans and land, boundaries that touch cause earthquakes. A transverse/transform boundary causes that.



The tectonic plates and continental drift theory largely was rejected, but as more evidence in the 1950s emerged, the debate was revived.



4 Scientific Developments that Reemerged the Theory:

  1. Ruggedness and youth of ocean floor discovered

  2. confirmation of repeated reversals of the Earth magnetic field in the geologic past;

  1. emergence of the seafloor-spreading hypothesis and associated recycling of oceanic crust;

  2. precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges.



Fossil Evidence

Glaciers

Glaciers flow from the ocean (first from land)