Unit 2: Internal Process Chapter 6 “ The Active Earth Plate Tectonics”

Quote "Rocks are records of events that took place at the time they formed. They are books. They have a different vocabulary, a different alphabet, but you learn how to read them." John McPhee "With their four-dimensional minds, and in their interdisciplinary ultra verbal way. geologists can wiggle out of almost anything.“ Lee Mediano

6.1 Alfred Wegner “Continental Drift” November 1, 1880 – November 1930 polar researcher, geophysicist and  Meteorologist 1912 ( Continental Drift Hypothesis) Figure 6.I The African and South American coastlines appear to fit together like adjacent pieces of a jigsaw puzzle on Wegener's reconstruction map. The red areas show locations of distinctive rock types in South America and Africa. The brown regions arc the continental shelves which are the actual edges of the continents.

Evidence: Fossils Laurasia Gondwanaland FIGURE 6.2 Geographic distributions of plant and animal fossils on Wegener's map indicate that a single supercontinent, called Pangea, existed from about 300 to 200 million years ago.

What Wegener could Not Prove? Mechanism for Continents to move Why ? World War II (1950’s-1960’s) ( Submarines, GSN (Global Seismology Network), Geochronology, Magnetic Anomalies)

6.1EARTH’S LAYERS

6.1EARTH’S LAYERS

6.2 Sea Floor Spreading Hypothesis

6.2 Sea Floor Spreading Hypothesis

Sea Floor Spreading

6.4 The Theory of Plate Tectonics Briefly states: The lithosphere is a hard, hard rock about 100 km think, that floats on hot, plastic asthenosphere . Lithosphere is broken in 7 large segments “Tectonic Plates” “Lithospheric Plates” They move at speed 1-16 cm/year Plate Boundaries are defined by their Plate Motion Divergent Plate Boundary (Moving apart) Convergent Plate Boundary (Moving toward one another) Transform Plate Boundary (sliding next to each other)

6.5 Anatomy of A Plate A plate is a segment of the lithosphere; includes the upper-mantle and all the overlying crust Can carry both Oceanic or Continental Crust A plate is composed of hard, mechanically strong rock A plate floats on the hot plastic asthenosphere A plate margin is tectonically active. Earthquakes, Mountains ranges are common in plate boundaries, Tectonic plates move at rates from less than 1 to 16 cm /Year. ( Oceans and continents can be part of a plate) ( Example Manhattan Island is 9 meters farther from London than it was more than 225 years ago when the declaration of independence) was written )

6.6 Why Plates moves? Earth as Heat Engine Mantle Convection

6.7 Supercontinents *Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era *Pannotia looked like a V that faced northeast. Inside the V was an ocean that opened up during the break-up of Rodinia, the Panthalassic Ocean, an ocean that became the early Pacific Ocean.

6.8 Isostasy Vertical movement of Lithosphere The concept that the Lithosphere Is in floating equilibrium on the asthenosphere is called Isostasy Example of Evidence: Ice Age beaches in Scandinavian crust , They now lie well above sea level because the land rose as the ice melted

6.9 How Plate Movements Affect Earth Systems Volcanoes Earthquakes Mountain Building Migrating Continents and Oceans

Plate Tectonics Chapter 6 Class 2 of 2

2 Quotes Today America forms the longest and straightest bone in the earth's skeleton -Ellsworth Huntington Alexuss Smith Einstein Quote " Dr. Einstein, aren't these the same questions as last years physics exam?" Dr. Einstein:  "Yes, but this year the answers are different."   Graciela Mendez

Mechanism for Plate Tectonics Sea Floor Spreading (Mid Oceanic Ridge) Magnetic Anomalies Asthenosphere vs. Lithosphere Seismicity Age of Oceanic Crust vs Continental Crust Volcanoes

Divergent Plate Boundaries Mid Oceanic Ridge: Rifting in the Oceans

Mid Oceanic Ridge Mid-ocean ridges are present in all large oceans and form a system of submarine mountains over 60.000 km long, the longest linear elevations on Earth. More than 60% of the magmatic rocks of the Earth, approximately 20 km3/yr, are generated at these ridges. The name "mid-ocean ridge" is used for constructive plate boundaries in oceanic areas whether or not the ridge is precisely in the middle of an ocean. The central location of a mid-ocean ridge is only maintained in the absence of subduction near ocean margins as subduction would destroy the symmetry.

Age of Continents

Continental Rifting Splitting Continents: Rifting in Continental Crust Examples: East African Rift, Rio Grande Rift

Convergent Plate Boundaries Convergence of Oceanic Crust with Continental Crust Convergence of two plates carrying Oceanic Crust

Ocean – Ocean Collision

Ocean-Continent Collision

Convergent Plate Boundaries c) Convergence of two plates carrying Continents

Convergent Plate Margins of Earth

Transform Boundary: San Andres Fault

Animations Plate Boundaries Plate Tectonics Animations