Plate Tectonics Alfred Wegener Alfred Wegener discovered that

Plate Tectonics

Alfred Wegener • Alfred Wegener discovered that the eastern coast of South America and the western coast of Africa fit together like puzzle pieces • pieced all the continents together to form a super continent named Pangaea. • Using the remains of ancient organisms, showed that 200 million years ago the same kinds of animals lived on continents that are now oceans apart

Pangaea

Plate Tectonics • Earths stiff outer shell is called the Lithosphere. • It consists of the crust and rigid upper portion of the mantle • Made up of 7 large pieces called tectonic plates. • The theory describing the movement of plates is called tectonic plates theory.

Why Do The Plates Move? • One hypothesis suggests that plate movement results from convection currents in the asthenosphere. • Asthenosphere is the hot, plastic portion of the mantle. • Theory of Continental Drift– Earth’s Crust and upper mantle are broken into plates an move around on the lower mantle (asthenosphere)

Divergent Plate Boundaries • A divergent plate boundary occurs where two plates move apart; a gap is created • Hot magma rises from the asthenosphere and cools forming new lithospheric rock. • The two diverging plates then pull the new lithosphere away from the gap.

Sea Floor Spreading • Mid-Oceanic Ridges are mountain ranges that form at divergent boundaries in oceanic crust. Magma rises from between the two diverging plates and fills the gap. New oceanic crust forms a large central valley, known as a rift valley. • The most studied Mid-Oceanic Ridge is the Mid. Atlantic Ridge. – runs down the center of the Atlantic Ocean from the artic ocean to an area off the southern tip of South America • Also found at Great Rift Valley (Eastern Africa)

Convergent Plate Boundaries • Can be an oceanic plate diving beneath continental or oceanic plates. • Andes Mountains is an example when India plate slammed into Asia plate - oceanic plate is more dense & dives beneath the continental plate. - This process is subduction • Ocean trenches, mountains, and volcanoes are formed at subduction zones – High temps and pressure cause plate to melt and form magma

Ocean Trenches Strange fish found 5 miles down Sea cucumber 5 miles down Deepest fish ever found in a trench.

Convergent Boundaries cont’d. • • Collision zone – 2 plates of similar densities collide Causes upward thrust, forming a mountain range The Andes on the right and the Himalayas on the left. 2 types – Oceanic to Oceanic – Continental to continental Subduction zone Continental-continental collision

Convergent Boundary

Two Oceanic plates collide • Denser plate bends under the other forming subduction zone • Deep sea trenches form, new magma rises as an island arc of volacanoes. – Islands of Japan – Volcanoes and Earthquakes likely.

Two Continental Plates • Both plates less dense than asthenosphere, – No Subduction • Collide and crumple forming Mountain Ranges – Earthquakes Likely – Himalayan Mountains in Asia Why no volcanoes? ? ?

The Himalayas • The Himalayas are the tallest mountain range in the world. • They formed during the collision between the tectonic plate containing India and the Eurasian plate

Transform Fault Boundaries • The cracks in the Earth where the rocks move past one another are called faults • Faults can occur any area where forces in the lithosphere are great enough to break rock • When rocks move horizontally past each other at faults the boundary is called a transform fault boundary • Earth Quakes are caused by transform fault boundaries

Transform Continued • 2 types – Two plates slide past one another moving in opposite directions – Two plates moving in same direction but at different speeds – Earthquakes likely • San Andreas Fault in California is Pacific Plate sliding past North American Plate – Each plate moves about 5 cm a year.

Transform Fault Boundary

Support for Tectonic Theory • As molten rock pours onto the ocean floor, iron minerals, such as magnetite, align themselves parallel to Earth’s magnetic field. • Earth’s Magnetic field has reversed direction many times during its history. • Differently oriented bands of magnetic rock • The rocks are youngest near the ridge • The rocks are older farther away from the ridge • Polar Wander Maps

Support con. ’t • Rock formations on South Africa and South America have the same layers (these continents fit together in the puzzle) • Fossil evidence

Fit together like a puzzle

Boundary review • 3 Types of boundaries: