Continental Drift: The Beginning of Plate Tectonics

Theory of Continental Drift

Continental Drift Theory that the continents are drifting apart and towards each other Alfred Wegener Idea that all continents were all pieced together 245 million years ago Pangaea = “All Earth”

Continental Drift

Argument for and against Continental Drift Same fossils on different Continents Rock formations Climate conditions evidence Glacial grooves on separated continents Species could travel over “bridges” Rock cycle occurs Climate has cycles Glaciers covered majority of Earth

Ultimate Question How could gigantic continents move? What natural force could move entire continents?

An Answer: Sea Floor Spreading Process in which new oceanic lithosphere is created as older material is pulled away Process forces tectonic plates away from each other Creates mid-ocean ridges which are underwater mountain chains

Sea-Floor Spreading

Evidence for Sea-Floor Spreading Eruptions of molten material Magnetic strips in the rock of the ocean floor Ages of rock from drill samples

Magnetic Reversals Earth’s magnetic poles change place Mineral grains of molten rock align to the poles of Earth Rocks freeze trapping history of magnetic reversals

Question: ???? If new crust is being made at mid ocean ridges and the sea floor is spreading, then why isn’t the Earth’s surface getting larger?

Subduction at Plate Boundaries Subduction is a process in which the dense ocean floor sinks back into the mantle Occurs at deep-ocean trenches Convergent boundaries

Quiz: What are the three layers of the Earth Based on Composition? What are the 5 layers based on Structure? What is Pangaea? What process showed Continental Drift is correct?