PSC 1515 Chapter 8 Plate Tectonics

Earth’s Layers Part 1 Crust Mantle Core

Earth’s Layers – part 2 Lithosphere Asthenosphere Lower Mantle Outer Core Inner Core

Continental Drift – a Theory Once upon a time when the Earth was formed and had developed water and an oxygen atmosphere, the galaxy was enjoying the site of this water covered planet. Then all of the land formed one large continent. This continent was called Pangea. Slowly, very slowly, Pangea started to break apart. The pieces of the crust drifted across the top of the mantle forming multiple continents

Plates The Earth’s crust broke into several sections we call plates These plates float on the semi liquid mantle They move in three different ways. Convergent – move together to make mountains Divergent – move apart to make trenches Transform – slide past each other

Divergent Boundries Plates pulled apart Volcanoes create new crust material Magma fills in the empty space between Magma comes from athenosphere Seafloor spreading Mid Atlantic Ridge East African Rift Valley

Convergent Boundries Two plates move toward each other, one may move under the other (subducts) Decrease Earth’s crust Increase at Divergent = decrease at Convergent Produces volcanoes and mountains

Three kinds of Convergent Oceanic-oceanic – older plate subducts Forms ocean trenches – eg. Mariana Trench – 7 miles deep Inhabited by extremophiles- animals that can live at high temp and pressure. Often use H2S instead of O2 Form volcanic islands like Hawaii Oceanic-continental – oceanic crust subducts Forms some mountain ranges Cascade Range in NW Continental-continental – same kind of rock No subduction Forms mountains like Himalayas

Subduction zone

Transform Boundries Slide past each other Lithosphere (crust) neither created nor destroyed Most found in oceans Famous – San Andreas Fault

Ring of Fire The Ring of Fire is a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90% of all earthquakes occur along the Ring of Fire, and the ring is dotted with 75% of all active volcanoes on Earth.    The Ring of Fire isn’t quite a circular ring. It is shaped more like a 40,000-kilometer (25,000-mile) horseshoe. A string of 452 volcanoes stretches from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, and into New Zealand. Several active and dormant volcanoes in Antarctica, however, “close” the ring.

Volcanoes - Ring of fire

Earthquakes – Ring of Fire