Plate Tectonics

Layers of the Earth The Earth is made of several layers that can be classified by chemical and physical properties. The Lithosphere makes up the crust; Earth’s rigid outer shell.

There are two types of crust Continental Less dense, granitic composition Oceanic More dense, basaltic composition

The Lithosphere is broken into several large pieces called plates

Asthenosphere is plastic (ooey-gooey) layer under the lithosphere. It is part of the upper mantle. Under the asthenosphere is the mantle. Under the mantle there is a liquid outer core surrounding a solid inner core.

Continental Drift Alfred Wegener (1880 – 1930) According to Wegener’s hypothesis of continental drift, the continents had once been joined together to form a single supercontinent. He named the supercontinent Pangaea, meaning “all land”

Evidence Continents look like they fit together like a puzzle Several fossil organisms found on different land masses

More Evidence Matching rock and mountain belts across continents Glacial till deposits across most continents

But there was a problem! His hypothesis did not become accepted until after he died  Why do you think Wegener’s hypothesis faced a great deal of criticism at the time?

Answer: He could not explain how the land was moving!

New Data! During the early 1900’s, Sonar made it possible to map the ocean floors deep-ocean trenches and mid-ocean ridges were discovered In 1963, Harry Hess published his hypothesis for sea-floor spreading: new ocean floor forms along ridges and slowly move outward

Evidence for Sea-Floor Spreading Patterns of earthquakes near trenches (where 1 plate goes under another plate) Paleomagnetism - the study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials.  - As rocks form, the iron-rich minerals align with Earth’s magnetic poles - As the poles move, the mineral alignment also moves - Bands/Stripes of opposite polarity form in ocean floor rock.

Age of ocean floor Oldest rocks are near the perimeter of ocean basins Newest rocks are near mid-ocean ridges

Go Wilson! Canadian geologist J. Tuzo Wilson (1908 – 1993) explained the “HOW?!” Suggest the lithosphere is broken into plates Movement of the plates is driven by convection currents in the mantle (asthenosphere)

Plate Tectonics Earth’s lithospheric plates move slowly relative to each other, driven by convection currents in the mantle.