Download Dynamic Earth Interactive Notes Earth`s Structure Plate Tectonics

Dynamic Earth Interactive Notes
Objectives: [8.9A] Describe the historical development of evidence that supports plate tectonic theory. [8.9B]
Relate plate tectonics to the formation of crustal features.
Earth’s Structure
Cross Section
Plate Tectonics
Alfred Wegener – suggested that the Earth’s continents were once joined together in one large mass he called
Pangaea using the following evidence:
o Coastlines of Africa and South America fit together
o Same plant and animal fossils on coastlines
o Similar geologic features on both coastlines
Plate Tectonic Theory – States that Earth’s outer layer, or lithosphere, is broken into several large slabs called
plates.
Plates and Boundaries
-
Continental Crust – Crust that makes up the continents. (20-40 miles thick)
Oceanic Crust – Crust that makes up the ocean floor. (4-6 miles thick)
Boundary – Border between two tectonic plates
 3 types of Plate Boundaries
Convergent Boundary
Divergent Boundary
Transform Boundary
Slip, Slide and Collide
Convergent Boundaries
Subduction Zones and Volcanoes

Form when oceanic crust is involved
Lithosphere – Rigid outer layer of the Earth broken
up into tectonic plates.
Asthenosphere – Hot, semi-liquid zone of the mantle
on which the tectonic plates float.
Subduction Zone – The area where one plate is being
pulled under the edge of another plate at a convergent
boundary.
Trench – a deep oceanic trench, or valley, that forms at a subduction zone as the oceanic crust sinks under the
other tectonic plate.
Island Arcs – Chains of volcanoes that form at the
subduction zone in the ocean between two oceanic plates.
Tsunami – a huge ocean wave caused by a sudden shift on
the ocean floor, such as an undersea earthquake.
Collision Zones and Mountains
Form when only continental crusts collide.

Continental crust is less dense than
oceanic crust therefore does not subduct
and causes the rock to crunch and fold
upwards forming mountains.

An example is the Himalayan mountain
range where the continental crust of the
Indian plate is colliding with the
continental crust of the Eurasian plate.
Divergent Boundaries – Spreading Plates

Tectonic plates are moving away from each other.
In Oceans: Seafloor Spreading – Occurs at divergent boundaries in the middle of the oceans at features
called mid-ocean ridges where oceanic crust is pulled apart as magma comes up from the mantle forming new
oceanic crust.
On Land:
Rifts – Valleys that form when two continental plates move apart at divergent boundaries.
Transform Boundaries – Grinding Plates

Tectonic plates grind past each other in a horizontal direction forming a fault – a crack or fracture
in the earth’s crust that is associated with this movement.
Faults and Earthquake
Faults produce many earthquakes, the shaking and trembling of the earth’s crust caused by the sudden
movement of plates as they build up stress at transform boundaries.
These are called Strike-Slip Faults.

Example – San Andreas Fault in California