Plate Tectonics: Earth's Plates and Continental Drift

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Plate TectonicsEarth's Plates and Continental
Drift
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• Some questions we will answer today
• How is the earth always changing?
• What does the interior of the Earth look like?
• What forces inside the earth create and change
  landforms on the surface?
• What is the theory of plate tectonics and how
  does it work?
• What happens when the plates crash together, pull
  apart, and slide against each other?

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The Earths Layers

• The Earth is made of many different and distinct
  layers. The deeper layers are composed of heavier
  materials they are hotter, denser and under much
  greater pressure than the outer layers.
• Natural forces interact with and affect the
  earths crust, creating the landforms, or natural
  features, found on the surface of the earth.

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• Before we start to look at the forces that
  contribute to landforms,lets look at the
  different layers of the earth that play a vital
  role in the formation of our continents,
  mountains, volcanoes, etc.

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Earth's Layers (from outer to inner)
crust - the rigid, rocky outer surface of the
Earth, The crust is thinner under the oceans.
mantle - a rocky layer located under the crust
- .Convection (heat) currents carry heat from the
hot inner mantle to the cooler outer mantle.
Asthenosphere Upper portion of mantle that is
partly melted, continents float on this
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Earth's Layers (from outer to inner)
outer core - the molten iron-nickel layer that
surrounds the inner core. inner core - the
solid iron-nickel center of the Earth that is
very hot and under great pressure.
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DID YOU KNOW?
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• Most people know that Earth is moving around the
  Sun and that it is constantly spinning.
• But did YOU know that the continents and oceans
  are moving across the surface of the planet?
  Why????????
• Volcanoes and earthquakes as well as mountain
  ranges and islands all are results of this
  movement. Why????????

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• Plate
• Tectonics

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• Most of these changes in the earths surface
  takes place so slowly that they are not
  immediately noticeable to the human eye.
• The idea that the earths landmasses have broken
  apart, rejoined, and moved to other parts of the
  globe forms part of the
• plate tectonic theory.

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Plate Tectonic Theory
Scientists found a crack in the seafloor and the
two parts are moving in opposite directions,
carrying along the continents and oceans that
rest on top of them called tectonic plates. They
are moving very slowly, but constantly. (Most
plates are moving about as fast as your
fingernails are growing -- not very fast!)
Currently Earths surface layers are divided into
nine very large plates and several smaller ones.
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Earthquakes match up with plate boundaries Note
the high of quakes around the Pacific in the
Ring of Fire
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• According to the theory of plate tectonics, the
  earths outer shell is not one solid piece of
  rock. Instead the earths crust is broken into a
  number of moving plates. The plates vary in size
  and thickness.

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• The North American Plate stretches from the
  mid-Atlantic Ocean to the northern top of Japan.
  The Cocos Plate covers a small area in the
  Pacific Ocean just west of Central America.
• These plates are not anchored in place but slide
  over a hot and bendable layer of the mantle.

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Why do the plates move?
The plates move due to convection currents. The
mantle material closest to the core is hotter so
it rises and displaces the cooler material above
in the asthenosphere which sinks. This slowly
drags the plates along with it.
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So what happens when the tectonic plates move?
It depends on what kind of crust it is (oceanic
or continental) and whether they are A.
Colliding (Convergent boundary) force is
compressional B. Pulling Apart (Divergent
boundary) force is tensional C. Sliding past
each other (transform plate boundary), force is
shearing
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Theyre Pulling Apart!

• When plates pull away from one another they form
  a diverging plate boundary, or spreading zone.

Thingvellir, the spreading zone in Iceland
between the North American (left side) and
Eurasian (right side) tectonic plates. January
2003.
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Ocean Crust meets Continental Crust

• Because continental crust is lighter than oceanic
  crust, continental plates float higher.
• So when an oceanic plate meets
• a continental plate, it slides
• under the lighter plate and
• down into the mantle. The
• slab of oceanic rock melts when the edges get to
  a depth which is hot enough. This process is
  called subduction.

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• Molten material produced in a subduction zone can
  rise to the earths surface and cause volcanic
  building, mountains, and islands.

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Converging...They Crash! And theyre both
Continental Plates

• When both are continental plates, the plates push
  against each other, creating mountain ranges.

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They meet and slide past each other!

• Sometimes, instead of pulling away from each
  other or colliding with each other, plates slip
  or grind past each other along faults. This
  process is known as faulting.

Earthquakes often happen at the sites of these
transform boundaries.
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You get earthquakes at the boundary where the 2
plates slide past each other