Transcript The Earth`s Tectonic Plates and Continental Drift

The Earth’s Tectonic Plates
and
Continental Drift
Continental Drift
In the early 1900’s, German
scientist Alfred Wegener proposed a
theory that the continents once formed a
single landmass he called Pangaea.
He suggested they later broke apart and
drifted to their current positions.
Wegener’s theory became known as
continental drift.
The
Breakup
of
Pangaea
Wegener’s Theory
Based on Three Facts
1. He found fossils of several plants and
animals on different continents that could
not have crossed the oceans.
2. He noticed that South America and
Africa look like they fit together like
puzzle pieces.
3. He found rock formations in Africa and
South America that matched.
Plate Tectonics
The theory that Earth’s
lithosphere is divided into
tectonic plates that move around
on top of the asthenosphere.
Origins in Wegener’s work on
continental drift.
Three Possible Driving Forces
of Plate Movement
Convection Currents
Ridge Push
Slab Pull
Convection Currents
Hot, rising currents
push the tectonic
plates apart.
Cooler, sinking
currents pull
tectonic plates
together.
Ridge Push and Slab Pull
Ridge Push – At mid-ocean ridges, the oceanic lithosphere is higher than it is
where it sinks into the asthenosphere. Because of ridge push, the oceanic
lithosphere slides downhill under the force of gravity.
Slab Pull – Because oceanic lithosphere is denser than the asthenosphere,
the edge of the tectonic plate that contains oceanic lithosphere sinks and pulls
the rest of the tectonic plate with it in a process called slab pull.
Plate Boundary
The area where two different
tectonic plates meet.
Three Types of Plate
Boundaries
1.
Convergent Boundaries – when two
tectonics plates collide.
Continent-Continent
Continent-Oceanic
Oceanic-Oceanic
2.
Divergent Boundaries – when two tectonic
plates move away from each other.
A crack, called a rift, forms between them.
New crust is formed as magma rises up through the rift.
3.
Transform Boundaries – when two tectonic
plates slide past each other.
Sea-Floor Spreading
The process by which the oceanic crust
separates and magma rises from the
mantle to form new crust.
Causes underwater mountain chains
called mid-ocean ridges.
The magma cools, builds up, and forms an
underwater mountain chain.
How Do We Know the SeaFloor is Spreading?
Magnetic reversals show sea-floor
spreading.
Also the best evidence for the theory of
continental drift.
Mid Ocean Ridges
Questions?????
What were the three things that made
Alfred Wegener come up with the theory of
continental drift?
– 1. Fossils
2. Continents fit together 3. Rock Formations
What type of plate boundary is a midocean ridge?
– Divergent boundary
What are the other two types of plate
boundaries?
– 1. Convergent boundary
2. Transform Boundary
What was the name of Wegener’s
supercontinent?
– Pangaea