Plate TectonicsHow the Earth moves

The Definition• The theory of plate

tectonics states that the Earth’s lithosphere is divided into pieces called tectonic plates that move around on top of the asthensophere

• Plates are either oceanic or continental

These plates drift very slowly—centimeters per year

• Once, the world had one giant supercontinent, called Pangea and one giant ocean.

• Then, over time, the supercontinent spread out, forming the 7 continents we know today—this process is described as continental drift

Sea-floor Spreading

• Magma rises from the mantle and solidifies—forming new oceanic lithosphere.

• Once the magma has solidified into the rocky crust, it spreads out in either direction

Divergent Boundary

• This is the boundary between two plates that are spreading away from one another– Like the ones found

where sea-floor spreading occurs

Mid-Atlantic Ridge: A Divergent boundary

Convergent Boundary

• A convergent boundary is formed where two plates collide with each other

• Three combinations exist:– Continental/continental

– Continental/oceanic

– Oceanic/oceanic

The Three Collisions: Convergent Boundaries

Transform Boundaries

• A transform boundary can be found where two plates are sliding past each other horizontally– The most famous of

which is the San Andreas Fault

The San Andreas Fault—A Transform Boundary

How Mountains Form

Types of Mountains—Folded

• Folded mountains form at convergent boundaries where plates collide

• Rock squeezes against rock, pushing it upward

• These form the highest mountains in the world

Types of Mountains—Fault-Block

• When the crust is tense, the rock can break along a series of faults, causing large rock blocks to drop down lower than other rocks

Types of Mountains—Volcanic

• Volcanic mountains form when oceanic crust sinks into the asthenosphere by subduction

• These rock melts, forming magma

• This magma, under pressure, eventually rises and erupts through volcanic mountains

The Ring of Fire