Continental Drift

Continental Drift Theory Most other scientists did not feel Wegener’s theory was true. That was because Wegener couldn’t come up with a theory as to why the continents would move.

Plate Tectonics

Earth’s Major Plates EurasianCaribbean Australian-IndianSouth American PacificAfrican Juan de FucaAntarctic North American

Earth’s Major Plates

New Technology Supports Continental Drift Theory Earthquakes and volcanoes occur in concentrated areas. This suggests that the crust is divided into pieces. There are forces that push and pull the earth’s surface causing the continents to move.

Theory of Plate Tectonics Explains the movement of Earth’s plates Movement leads to the formation of volcanoes, earthquakes, ocean trenches, mountain formations, etc. Plates move 1-10 cm per year

What causes the plates to move? Convection currents in the mantle. Scientists generally agree that convection occurring in the mantle is the basic driving force for plate movement.

60 years ago, in the 1950’s, Sonar was invented.

Bats use it!

Sonar brought Wegner’s theory back to life!

Sonar made it possible for us to observe the ocean floor.

Soon, scientists observed a large mountain chain running down the center of the Atlantic ocean.

They quickly found that the ridge ran around the world They quickly found that the ridge ran around the world!

Sea- floor Spreading The longest chain of mountains in the world is the Mid-Ocean Ridge. The mid-ocean ridge extends into all of Earth’s oceans. Down the middle of the ridge is an area called the rift valley – It is almost twice as deep as the Grand Canyon.

Sea- floor Spreading Longest chain of mountains in the world is on the ocean floor (Mid-Ocean Ridge). At this ridge, the molten material rises from the mantle and erupts (much like a volcano). Molten material spreads out, pushing older rock to both sides of the ridge.

Sea Floor Spreading- Animation Makes the mid ocean ridge.

How do we know sea floor spreading exists? Earth is a Big Magnet

Atoms of iron (magnetite) in newly formed ocean crust lined up to the magnetic north.

Evidence of Sea-floor Spreading 1. Magnetic Stripes. How does the pattern of matching stripes show evidence of sea- floor spreading?

Evidence - Drilling Samples The Glomar Challenger did a drilling sample and found rocks that the farther away from the ridge the older the rocks were. The younger ones were in the center of the ridge.

2.Rock sampling- the further from the Mid Ocean Ridge the rocks are, the older they are; newer rocks in center of ridge

Pillow Lava forms when magma cools in water. This is evidence of volcanic activity!

Evidence Supporting Sea-Floor Spreading: 1. Molten material -on ocean floor provides evidence that new crust is forming. 2. Rock sampling- the further from the Mid Ocean Ridge the rocks are, the older they are; newer rocks in center of ridge 3. Magnetic stripes- show pattern of Earth’s magnetic poles reversing

2 TYPES OF CRUST 1) OCEANIC - under ocean - thin/very dense - very active - made of basalt 2) CONTINENTAL - under land - thick/less dense - constantly created and destroyed - made of granite

Types of Plate Boundaries 1) Divergent 2) Convergent 3) Transform

DIVERGENT 2 plates move AWAY from each other Forms volcanoes (mid-ocean ridge), cause of seafloor spreading and rift valleys.

Animation

If new crust is being added to Earth’s surface, is Earth getting bigger?

CONVERGENT 2 plates move toward each other (COLLIDING)

Continental-Continental Crust on continents have the same density, so they push against each other forming mountains. EX: Himalayan mountain range

Continental/Continental Convergence Found- India (Mt. Everest)

Continental-Ocean More dense crust of ocean is pulled beneath (subducted) the less dense continental crust. Forms trench in ocean Forms volcanoes on land Subduction zone animation

What is subduction? Subduction is the process by which the ocean floor sinks beneath the continental crust and back into the mantle. Seen in the US on the Pacific Coast.

Oceanic/Oceanic Convergence Found- Alaska (Aleutian Islands)

FYI Most ocean trenches are found in the Pacific Ocean. The deepest part of the ocean is the Marianna’s Deep. It is located in the Pacific Ocean The Pacific Ocean is shrinking, but it is still the Largest ocean

TRANSFORM 2 plates SLIDING HORIZONTALLY past each other Forms earthquakes

Transform – plates sliding horizontally past each other. Found- California (San Andreas Fault) Produces earthquakes!! All plates

Plate Boundary Animations eo/animations/ch2.htmhttp://www2.wwnorton.com/college/geo/eg eo/animations/ch2.htm