What is Plate Tectonics Theory?

What is Plate Tectonics Theory?

Use this part of the PPT for

p. 7 of your INB!!!

A. Continental Drift (Alfred Wegener)

Proposed large-scale movement of the continents

The Discovery of Plate Tectonics

Evidence:1. “Puzzle fit” of

continents to form “Supercontinents”a. Suess (1900)-

Gondwana

b. Wegner (1915)-Pangea

More Evidence…2. Similar rock ages3. Similar geologic

structures such as mountain ranges

4. Fossil Evidence from the Mesosaurus

5. Climate Evidence such as glacial deposits

**Wegener’s theory did not gain much support because he could not explain how the tectonic plates move

B. Seafloor Spreading- Henry Hess)1. Convection currents

move plates around2. Mantle source of

heat and convection3. proposed new and

recycled seafloor4. Evidence from

submarines during WWII around the Mid-Atlantic Ridge showed the seafloor is a mirror image on each side of the ridge

**There was no evidence for this theory, until…

Magnetic Pole Reversals or “Tape Recording”

1. Magnetic Reversalsa. Switching strength to the

south from the northb. Preserved in lava

because iron points towards stronger pole

c. Age of these iron bands can be calculated and if the seafloor is spreading from a center, they should be mirror images on each side of ridge

(continued)

2. Seafloor agesa. Speed = distance /

time

Mid-ocean ridge

4.0

3.0

2.0

Oceancrust today

Million years ago (Ma)

5.0

million

years old

3.3 2.50.7 0 0.7

2.5 3.35.0

Magnetic mapping can measure the rate of seafloor spreadingAn oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.

Mid-Atlantic RidgeHigh intensity

Low intensity

Magnetic mapping can measure the rate of seafloor spreadingAn oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.

Mid-Atlantic RidgeHigh intensity

Low intensity

A sensitive magnetometerrecords magnetic anomalies,…

Magnetic mapping can measure the rate of seafloor spreadingAn oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.

Mid-Atlantic RidgeHigh intensity

Low intensity

A sensitive magnetometerrecords magnetic anomalies,…

Iceland

Mid-AtlanticRidge

Magnetic mapping can measure the rate of seafloor spreadingAn oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.

Mid-Atlantic RidgeHigh intensity

Low intensity

A sensitive magnetometerrecords magnetic anomalies,…

Iceland

Mid-AtlanticRidge

…alternating bands of highand low magnetism.

Symmetrical bands on both sides. Why?

Looking at pole reversals preserved in the ocean floor

provides the evidence needed to support seafloor spreading.

Seafloor spreading provides the mechanism for “how” the continents move! (Wegener)

A Mosaic of PlatesA. Entire Earth’s surface

is made up of tectonic plates

A. Made up of a special layer of the Earth called the lithosphere and “ride” on top of the mantle

B. Plates have both oceanic crust & continental crust

A. Continental crust is less dense than oceanic crust

A Mosaic of Plates (cont.)C.Specific Geologic activities that occur

along plate boundaries or because of plate movement:1. Volcanoes2. Mountain building3. Earthquakes4. Hot spots5. Faults/cracks in crust