Plate Tectonics

1. Plate Tectonics Earth Science Charlotte Carter

2. Unit Review

3. Drifting Continents • Evidence of drifting • Fossils found on both of the continents of Africa and South America that are of the same organism • Fossils: The preserved remains of ancient organisms • German scientist Alfred Wegner came up with the theory of continental drift, he was actually a meteorologist and not a geologist • The theory called the giant landmass that once was on Earth Pangaea • Pangaea: Means all Earth • Early Earth & Plate Tectonics

4. Fossil Evidence • Fossils play a key role in supporting the theory of Continental drift • Glossopteris is an extinct plant • They are found in rocks that are around 250,000,000 years old ( 250 million) • The seeds were to large to be carried by wind and too fragile to have survived ocean waves • The fact that they are found in Antarctica implies that they had to be in a better climate than what is present Antarctica

5. Fossils • Glossopteris: a fern found on the southern continents • Cynognathus: a land reptile found in South America and Africa • Lystrosaurus: a land reptile found in Africa, Antarctica, and India • Mesosaurus: a freshwater swimming reptile found in Africa and South America

6. Geologic Evidence • From Rocks • Not only fossils provide evidence for theory support • Rocks in Africa and South America • When you examine the continents of Africa and South America,they look as if they could piece together like a puzzle • The layers of coal depth line up with each other • Rock deposits from glaciers also match

7. Naval oceanography made two significant contributions in the advancement of the theory of plate tectonics. • . 1. The charting of the ocean floor using echo sounding refined the understanding of seafloor structure 2. Studies of the sea floor using instruments called magnetometers revealed strong evidence in support of seafloor spreading. • Just as maps of the oceans and coastlines initiated the idea of continental drift, maps of the ocean floor propelled science into the investigation of seafloor spreading. Charts and studies of the mid ocean ridge system, trenches, seamounts, and continental shelves—have been examined and catalogued. • Using these and other data, Harry Hess and Charles Dietz proposed the idea of seafloor spreading. They suggested that the worldwide system of undersea mountains called the mid-ocean ridges is where new ocean floor is created as plates move apart. As they diverge, they move large crustal plates along with the continents that sit atop of them.

8. Divergent Boundary Spreading Sea Floor • Divergent Boundaries • Constructive-add new land • Mid-ocean Ridge • Ocean floor moves away on either side of the ridge • Called sea-floor spreading • Often offset by transform faults which causes a curve in the ridge Sea-Floor Spreading/Mid-Ocean Ridge Basic Plate Boundaries Transform Faults

9. Magnetic Rock Strips • Some minerals (such as magnetite) have magnetic properties • These minerals line up with the Earth’s magnetic poles • When the molten rock hardens, a permanent record of the Earth’s magnetism remains • The Earth’s magnetic poles have reversed themselves from time to time • Animation • Sea Floor Spreading

10. Convergent Boundaries • Plates collide-destructive • Two continents colliding build mountains or plateaus • The Indian Plate and the Eurasian Plate collide to form the Himalayas which have Mt. Everest , the highest mountain on Earth.

11. Convergent Boundary • Destructive-crust is destroyed (melted by the mantle) • Called Subduction • When oceanic and continental crust collide • Oceanic crust is pushed down into the mantle and melted • Some of this melted material surges upward

12. Convergent Boundaries • The continental crust is also forced upward producing volcanoes • The Cascade Range in Washington and Oregon are an example of this Convergent Boundaries

13. Convergent Boundaries • When two oceanic plates collide subduction occurs • The older denser plate is pushed into the mantle and melted • Some of the material rises upward and erupts on the ocean floor forming an island arc

14. Theory of Plate Tectonics • Tectonics: refers to the branch of geology that is concerned with plate movements • Theory of Plate Tectonics: Links together the ideas of continental drift and ocean floor spreading to explain how the Earth has evolved over time. • It explains the formation, movements, collisions, and destruction of the Earth’s crust • According to the theory the Earth’s uppermost layer, called the lithosphere, is made up of plates

15. Lithospheric Plates • There are seven major plates • The Pacific Plate- • which covers 1/5 of the Earth • North American • South American • Eurasian • African • Indo-Australian • Antarctic Plates • There are also Many smaller plates • Caribbean • Arabian • Plate Tectonics Review

16. SUMMATION • The theory of plate tectonics is relatively new • Early 1900s, Alfred Wegener first developed a theory of continental drift based on a collection of evidence from rocks and fossils found on continents separated by vast distances • 1928, Arthur Holmes proposed a mechanism to explain how the continents could have moved across Earth's surface • Circular convection currents of molten material deep within Earth could provide ample force to divide and move continents • By the late 1960s, evidence of seafloor spreading helped to support the now well-accepted theory of plate tectonics.