The Theory of Plate Tectonics Based on two hypotheses Continental Drift Seafloor spreading

Continental drift hypothesis: evidence? Proposed in 1911 All evidence found on the continents Mechanism for moving the continents was not known

Continental Drift Hypothesis Alfred Wegener proposed the hypothesis of continental drift in 1911 He gathered information from many different sources and used it as evidence for his hypothesis

Continental Drift Hypothesis Fit of the continents Fossil evidence Ancient mountain ranges Past climate evidence Swamps formed in tropical regions Glaciers formed at the south pole

The continental drift hypothesis proposes that the continents were assembled to form the super continent Pangaea. Moved through time http://www.youtube.com/watch?v=WaUk94AdXPA

Fit of Continents Antonio Snider-Pelligrini (1858), a geographer cut out a map of Africa and South America suggesting they were connected at one time Other physical evidence based on observation was used by Wegener

Fossil Evidence Similar terrestrial species were found on many continents now separated by oceans. Information collected by paleontologists

Ancient Mountain Ranges The same sequence of rocks is found in North America, Great Brittan, and Norway. The pattern does not make sense with the continents in their current configuration.

Evidence of Ancient Glaciers Glaciers carve the rock as they move. Scientists can determine the direction of movement (notice the direction of movement noted in South America) As South America sits today, the pattern would not make sense. (glaciers do not move from sea level to higher elevations)

Lack of mechanism to explain continental movement. Evidence implied that the continents were at one time assembled Wegener’s idea was not accepted by the scientific community because he could not explain how the continents moved With advances in technology, new information was gathered in association with WWII

Exploration of the Ocean Basins What information do you know regarding the seafloor that may be used to help understand the hypothesis of seafloor spreading?

Exploration of Ocean Basins Ocean basins contain a variety of landforms not discovered until WW II.

Seafloor features were discovered using sonar. Support Seafloor features were discovered using sonar. 4:26 Echo sounding was used to map the seafloor

Oceanic crust is composed of volcanic rock. Pillow basalts Basalt is volcanic rock with a mafic composition. Higher percentages of iron and magnesium, lower percentages of silicon and oxygen.

Seafloor Spreading In the 1963, Harry Hess developed the idea of seafloor spreading to explain the seafloor’s formation Continental movement is the result of ocean floor movement

Seafloor Spreading Mafic lava is extruded along the mid-oceanic ridge to produce ocean floor. New material is added, the cooler material is split and is “pushed” away from the ridge

Driving Mechanisms Convection cells within the mantle Push Pushing at the mid-oceanic ridges Pull Pulling at the subduction zones Convection

The theory of plate tectonics Explains that the Earth’s lithosphere is broken into distinct units that move as a coherent package. Where the tectonic plates meet, produces distinct physical characteristics on the Earth’s surface.