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Who believes in plate tectonics?

Evidence: Fossils

Matching Mountain Ranges 4

Glacier Evidence 5

What is the Mid-Atlantic ridge?

A new hope: Sea-Floor Spreading MID-ATLANTIC RIDGE 50,000 km. Long mountain range on the ocean floor

Spreading Center 8

New Ocean forming – linear Red Sea When it grows up, it will be like the Atlantic Ocean

In Afar, Ethiopia, a 40-mile magmatic rift that opened up 1 year ago

Which graph best represents the geologic age of the surface bedrock on the ocean bottom?

Mid-ocean ridges (rifts) normally form where tectonic plates are (1) converging (3) stationary (2) diverging (4) sliding past each other

If new crust is created at divergent boundaries, is earth getting larger? CONVERGENT BOUNDARIES – DESTROYS CRUST Oceanic Crust converging with Continental Crust Oceanic crust converging with Oceanic Crust Continental Crust converging with Continental Crust

OCEAN CRUST - CONTINENTAL CRUST SUBDUCTION – TRENCH FORMS

Oceanic-Continental Convergent Boundary - SUBDUCTION DENSER OCEANIC CRUST GOES DOWN INTO MANTLE 15

OCEAN CRUST –OCEAN CRUST CONVERGENCE - SUBDUCTION

Oceanic Crust – Oceanic Crust Older, denser oceanic crust is SUBDUCTED (sinks below) VOLCANIC ISLAND ARC FORMED – ALEUTIAN ISLANDS TRENCH FORMS

Continental Crust – Continental Crust Convergent Boundary NO SUBDUCTION - COLLISION ZONE WHY YOU FIND MARINE FOSSILS ON TOPS OF MOUNTAINS 18

Collision of India and Asia 19

f07_58_pg196 Convergent Indian-Australian Plate and the Pacific Plate (oceanic crust to oceanic crust) are converging forming the Tonga Trench. Deep EQ’s f07_58_pg196.jpg f07_58_pg196 20

3 types of plate boundaries caused by convection currents CASCADES MID-ATLANTIC RIDGE TRENCH

Can magnetic poles really switch?

Evidence for Plate Tectonics During WWII, the U.S. in an effort to find any advantage that would help out submarines in the war effort, scientists found that the iron in the rock at the mid-ocean ridge sometimes pointed North and sometimes pointed South Lava is a mixture of melted minerals of which Iron is a very common one. Iron is attracted to the Earth’s magnetic North Pole and prefers to line up with Earth’s magnetic field. While lava is liquid, the bits of iron will tend to line up with a magnetic orientation pointing at the North Pole. When the lava solidifies, the magnetic orientation is frozen into the rock- essentially; it will have a “north end” and a “south end.” Back in World War II, the United States, in an effort to find any advantage that would help out submarines in the war effort, collected any type of data possible about the ocean and ocean floor. When they dragged a magnetic detector along the ocean floor, they discovered that the rocks making up the ocean bottom either had a magnetic orientation pointing to the North Pole or to the South Pole. As the magnetic detectors were dragged along the ocean floor, the orientation of the rock flipped from North to South- but never any other direction. They discovered a very quirky behavior of our planet: for some still-unexplained reason, at random times in Earth’s past, the magnetic orientation of the planet reversed- several times. In other words, if you traveled back in time with a compass, sometimes it will point north and other times it will point South. The significance of these two points becomes clear when we have a map of the magnetic orientation of the entire Atlantic Ocean floor. Imagine that the North-oriented rocks (usually referred to as “normal polarity”) are colored white while the South-oriented (“reversed polarity”) rocks are colored black. What we will see is a striped pattern which runs parallel to the coasts of the Atlantic shores. In addition, the magnetic stripe pattern that emerges as we cross the Atlantic floor from the USA to the Mid-Atlantic Ridge is an exact mirror-image of the pattern from the Mid-Atlantic Ridge to Europe. This implies that the ocean floor is splitting at the Mid-Atlantic Ridge, new rock is being made at the ridge, and the new rock (along with its magnetic orientation) is split and each half is carried away from the ridge as the ocean floor spreads. 23

How could this be? Basalt is iron rich and contains magnetite. Magnetite acts like a little magnet and aligns itself with the orientation of earth’s magnetic field. When magma solidifies, the alignment is “locked in” recording Earth’s magnetic orientation at the time of cooling.

MAGNETIC STRIPE EVIDENCE North Oriented Rocks are said to have NORMAL POLARITY South Oriented Rocks are said to have REVERSED POLARITY

The earth’s magnetic field has reversed hundreds of times

More Evidence for Plate Tectonics  Hot Spots A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands. Hot spot evidence supports that the plates move over the Earth’s surface.

HOT SPOTS Major regions of volcanic activity in the interior of plates away from plate boundaries. The cause of these hot spots is thought to be plumes of magma rising up from mantle producing sites of active volcanism. As the plate moves over a hot spot, a chain of volcanic mountains forms, like Hawaiian Islands

Hot spots: http://plainedgeschools.org/swells/plate%20tectonics%20-%20revised.ppt#367,59,Slide 59

This diagram provides evidence that the Pacific Tectonic Plate is moving toward the (1) south (3) southwest (2) east (4) northwest