Transcript Plate Tectonics

Plate Tectonics
Plate movement is driven by convection currents.
Convection Currents
 Currents are caused by heat in Earth’s interior
 Hotter material is less dense, rises toward the
surface
 Cooler material pushed out of the way, sinks
back toward the core
 Lithosphere is pushed up and melted above
rising convection currents
 Lithosphere is pulled downward above sinking
currents
Convection connection
 New crust is formed where magma is
rising at Divergent boundaries
 Old crust is destroyed where magma is
sinking at Convergent boundaries
SEA FLOOR SPREADING
• Creates a mid-ocean ridge (MOR)
• New crust is forming at the center of
the ridge
• Age of crust increases as distance
from ridge increases
Sea floor age
Sea Floor Spreading
The sea floor in the center of the
ridge is the youngest material.
As you move toward the coastlines,
the sea floor is made of older
material.
Magnetic Reversals
Lava forming on the seafloor
contains iron oxide which points to
magnetic north when it cools and
hardens.
These rocks provide a record of
where magnetic north was located
when the lava was formed.
Magnetic Reversals
 Scientists can match up the bands on
either side of the mid-ocean ridge to
prove that the seafloor is spreading.
 Scientists have also found that the
bands alternate between pointing
north and pointing south. This
indicates that the Earth’s magnetic
poles have reversed many times.
Measuring magnetic field in ocean
floor
The earth's magnetic field has
reversed approximately 170 times
over the last 100 million years.