Chapter 4 Section 3
THEORY OF PLATE TECTONICS
Language of the discipline
lithospheric plate: a large brittle piece of Earth’s outer shell
plate tectonics: theory that explains how lithospheric plate move and
cause major geologic features and events on Earth’s surface
ocean trench: long, deep parts of the seafloor
Slab: plate that sinks back into the mantle
Global Positioning System (GPS): a network of satellites used to
determine locations on Earth
Language of the discipline
continue……

Convection: heat transfer by the movement of matter from one
place to another

Define: to fix or mark the limits of
Earth’s Plates

Lithospheric plates are large brittle pieces of Earth’s outer shell.

The theory of plate tectonics explains the movement of lithospheric
plates.
Boundaries of Lithospheric Plates

Mid-ocean ridges show boundaries of some lithospheric
plates
•. Earthquakes and volcanoes occur where the edges
of plates are pushed together, pulled apart, or slide
horizontally.
• Ocean trenches are the deep parts of the seafloor
where numerous earthquakes and volcanoes occur.
• Seafloor is formed at ridges and destroyed at ocean
trenches.
Boundaries of Lithospheric Plates
(cont.)
Types of Lithosphere

Oceanic Crust: thinner than continental, made of dense igneous
rock covered by a thin layer of sediment (sand & dirt)

Continental Crust: thicker than oceanic; made of igneous and
metamorphic rock covered by sedimentary rock
What controls plate movement?

Some scientists believe that convection controls the movement of
plates.
What controls plate movement?
(cont.)

Temperature increases with increasing depth.

Radioactive decay is one important source of internal heat.

Heat increases the temperature of rock which decreases
the density.
Plate Movement and Convection

Slabs are cooler, denser lithospheric plates that
sink down into the mantle.

They bend and break as they sink down into the
mantle, causing earthquakes.
Ridge Push and Slab Pull

Convection: Cooler, denser masses of rock sink, bringing
plates with them. Less-dense rock is brought to the
surface at mid-ocean ridges.

Ridge Push: The force of gravity moves the plate
downward and away from the mid-ocean ridges.

Slab Pull: Gravity acts on denser plates, pulling them into
the mantle.
Ridge Push and Slab Pull
Plate Movement

•
•
Global Positioning System (GPS) is a network of satellites using radio
waves to determine locations on Earth.
Measures the movement of plates
Using GPS and satellite laser ranging (SLR), plate movement has
been estimated at a few centimeters per year.
GPS & Satellite Laser Ranging in
Plate Tectonics

GPS (Global Positioning System) is a network of satellites
that uses radio waves to measure the direction and
speed of plates as they move along Earth’s surface.

Satellite Laser Ranging (SLR) uses laser beams to
measure the distances of plate movements.
Checking for Understanding

1. What does the theory of plate tectonics explain?

2. What two types of lithosphere make up Earth’s surface ?

3. Why does the density of the surrounding rock decrease (Think
slabs?)

4. What are GPS?

5. Use the term slab and ocean trench in a sentence.

6. A method used to determine the rate of plate movement is
______.

7. On the back of your paper draw a compare and contrasting
thinking map of the following: Convection, Ridge Push, and Slab
Pull.