Transcript Plate Tectonics and Continental Drift

Plate
Tectonics and
Continental Drift
Continental Drift
• Alfred Wegener believed that the
continents were once connected.
• This large continent was called
Pangea.
• In 1915, he proposed his theory of
Continental Drift.
Evidence For Continental Drift
• Matching fossils were found
along the boundaries of
continents that have very
different climates.
• Glacial deposits found in South
America, Africa, India, and
Australia.
Sea Floor Spreading Theory
• With sonar, scientists determined that the
ocean floor was composed of mountains
and deep valleys.
• Harry Hess authored the Sea Floor
Spreading Theory to explain that the ocean
floor is constantly spreading along the MidAtlantic Ridge.
Mid-Atlantic Ridge
• New sea floor is created by oozing magma in
the center of the MAR.
• Old sea floor is forced down into the mantle in
the trenches near the boundaries of the
oceans and continents.
• Rocks near the MAR were much younger
than rocks that had been forced outward from
the MAR.
Plate Tectonic Theory
• A new theory based on the Sea Floor
Spreading Theory and The
Continental Drift theory were
combined to form the Plate Tectonic
Theory.
• Plate Tectonic Theory: States that the
earth’s crust and upper mantle are
broken into sections called plates. The
plates move around on the mantle.