Science Plate Tectonics

Be prepared to discuss and debate for each point on Tuesday Homework Write two paragraphs: One – give supporting details as to why you believe in the theory of continental drift. Two – give supporting details why you do not believe in the theory of continental drift. Be prepared to discuss and debate for each point on Tuesday

Geologists are scientists who study the forces that make and shape the planet Earth. Geologists study the Earth’s interior through seismic waves.

What is the Lithosphere? The crust and part of the upper mantle = lithosphere 100 km thick Less dense than the material below it so it “floats”

Alfred Wegener

D. Alfred Wegener – proposed that in the distant past, the Earth’s continents were all joined as a single landmass. 1. Evidence for his theory South America and Africa would fit remarkably well, shoreline to shoreline. If the Americas were moved next to Africa and Europe, there would be a match of ancient continental rocks and tectonic (fold and fault) structures. c. Pangaea – when Wegener placed all the continents together like a puzzle, it formed a large landmass which he called Pangaea.

Fossil Evidence

Wegener’s theory was rejected by scientists because he could not explain what force pushes or pulls continents.

Fossils of tropical plants found on an island in the Arctic Ocean are evidence for the theory of continental drift.

2 Types of Plates Ocean plates - plates below the oceans Continental plates - plates below the continents

Questions... What is the theory of plate tectonics? What is the lithosphere? What are the two types of plates?

Plate Boundaries

Divergent Boundaries Boundary between two plates that are moving apart or rifting   RIFTING causes SEAFLOOR SPREADING

Features of Divergent Boundaries Mid-ocean ridges rift valleys fissure volcanoes

Convergent Boundaries Boundaries between two plates that are colliding   There are 3 types…

Type 1 Ocean plate colliding with a less dense continental plate Subduction Zone: where the less dense plate slides under the more dense plate VOLCANOES occur at subduction zones

Andes Mountains, South America

Type 2 Ocean plate colliding with another ocean plate The less dense plate slides under the more dense plate creating a subduction zone called a TRENCH

Aleutian Islands, Alaska

Type 3 A continental plate colliding with another continental plate Have Collision Zones: a place where folded and thrust faulted mountains form.

Transform Fault Boundaries Boundary between two plates that are sliding past each other EARTHQUAKES along faults

San Andreas Fault, CA

Questions... What are the three types of boundaries? What direction do plates go for each? Which boundary has a subduction zone…what occurs at a subduction zone?

Causes of Plate Tectonics

Convection Currents Hot magma in the Earth moves toward the surface, cools, then sinks again. Creates convection currents beneath the plates that cause the plates to move.

Questions... What causes plates to move? How is a convection current formed?

C. Why do the plates move? Due to tremendous heat, rock in the asthenosphere is like hot taffy This allows plates to ride on top of hot, flowing rock. 3. Plates move because heat is being released from deep inside the earth. 4. Convection currents causes hot material to rise and expand (plates diverge) and cooler material to sink and contract (plates converge).

The mid-ocean ridge is the longest chain of mountains. Most of the mountains in the mid-ocean ridge lie hidden under hundreds of meters of water. Hess proposed that the ocean floors move, carrying the continents along with them. The movement begins at the mid-ocean ridge. At the mid-ocean ridge, molten material rises from the mantle and erupts.

When a divergent boundary develops on land, two of Earth’s plates slide apart. A deep valley called a rift valley forms along the divergent boundary. A convergent boundary is where two plates come together, or converge. The result of the plates hitting together is called a collision.