How does the Earth’s Surface Change? The Dynamic Earth and Plate Tectonics Theory

Evidence For Change: Deformed Strata (layers of rock) Seismic Activity Subsidence or sinking of the crust (Gulf of Mexico) Uplift of the crust (mountains)

Discoveries Leading Up to the Theory of Plate Tectonics: Continental Drift Sea Floor Spreading Paleomagnetic Data and Polar Wandering Reversals in Magnetic Polar Polarity

Continental Drift Theory Proposed by German Scientist Alfred Wegner in 1915 States that all continents were originally one land mass called Pangea Was a radical theory at the time

Supportive Evidence for Continental Drift Fit of coastlines Matching fossil evidence Matching paleoclimates Matching rock and mineral type and structural similarities

Strengths of Continental Drift Theory: Continents do really seem to fit together like a giant puzzles Matching evidence from either side of Atlantic Ocean in Africa and South America of fossil remains, rock and minerals, paleoclimates etc…

Weaknesses of Continental Drift Theory: Wegner could not explain how or why continents moved…

Polar Wandering Data Mid-50’s- scientists produce paleomagnetic data from several continents showing the apparent polar wandering consistent with Alfred Wegner’s theory (magnetic north poles changed position over time)

Sea Floor Spreading Harry Hess from Princeton University proposed that sea floor is spreading apart. This spreading was thought to be caused by convection currents in the mantle (1962)

Magnetic Reversals on seafloor Pattern of magnetic polar reversals found on sea floor in 1963 Connects to idea of sea floor spreading by Harry Hess Reversals coincide with age of rock on sea floor

Unified Theory of Plate Tectonics… All previous ideas can be explained by this theory Term “Plates” was coined in 1960’s by J.Tuzo Wilson of the University of Toronto

Main Points of the Unified Theory of Plate Tectonics: Surface of the Earth is composed of major rigid moving sections called “plates” These plates “float” on the mantle The plates consist of continental and oceanic rock The boundary where the plates meet is the area of the most crustal activity Differences in the density of materials in the asthenosphere move the plates

Three type of plates motions: Convergent Divergent Transform See ESRT page 5 -Moves away -Moves together -Slides past

How do the Plates Move? Type of MotionHow Plate is Moving Example Convergent Divergent Transform

Earth’s Lithospheric Plates Wrap up: What is one new idea you learned about today?