WHAT IS THE THEORY OF CONTINENTAL
DRIFT?

the idea that the continents were once all joined
together in one super-continent called Pangaea
and slowly moved to their current positions
CONTINENTAL DRIFT- ALFRED WEGENER

Alfred Wegener
Evidence of “continental drift”—
.
•Physical fit of continents
•Fossil evidence
•Rock layer sequences
•Glacial evidence
•Coal Deposits in Antarctic
Alfred Wegener
Proposed theory 1912
Shoreline Fit of the Continents
http://www.abdn.ac.uk/zoohons/lecture1/img008.GIF
FOSSIL EVIDENCE
The fossils from the exact same animals are found on continents separated by vast oceans.
A Palm tree
preserved in
the cliffs of
Nova Scotia
Canada.
MATCHING ROCK LAYERS
Matching Mountain
Ranges
GLACIER EVIDENCE
Glaciers scars are found on continents
which are today too warm for glaciers.
CONTINENTAL DRIFT- ALFRED WEGENER

Alfred Wegener
HARRY HESS AND THE GLOMAR CHALLENGER
Sediment gets older towards the edges of continents
MAGNETISM
EVIDENCE OF SEA FLOOR
SPREADING

Radiometric Dating


Sediment Samples


Higher temps @ ridges
Magnetic Anomalies


Sediment layers thicker further away from ridges
Rheology


Older rocks further from ridges
Poles reverse, magnetic minerals frozen in place as rock
cools and hardens
Direct measurements of plate movement
IF WEGENER ONLY KNEW
THE CRUST



Outer layer
5-100 km thick
2 types of crust


Oceanic (very dense,
made of basalt)
Continental (less dense,
made of granite)
CONVECTION CURRENTS MOVE THE PLATES
Watch Convection Currents of Magma Move the Tectonic Plates
What landforms are associated
with a diverging plate boundary
between two ocean plates?
MID-OCEAN RIDGE
What land forms are associated
with a transforming plate boundary
between two continental plates?
EARTHQUAKES
FAULT LINES
What land forms are associated
with a converging plate boundary
between a continental plate and
an oceanic plate?
TRENCH, VOLCANOES OR MOUNTAINS
TRENCHES
http://www.thirteen.org/savageearth/hellscrust/assets/images/ringoffire.jpg
What landform(s) are
associated with converging
boundary between two
continental plates?
Mountains
What landform(s) are
associated with converging
boundary of two oceanic
plates?
Trench and Island Arc
Aleutian Islands
Japan and Mariana Trench
HOT SPOTS
Tectonic plate moves
slowly over the Hot Spot