Plate Tectonics and the Theory of Continental Drift

Wegner named this supercontinent Pangaea.

Pangaea 200 to 300 Millions of Years Before the Present

Evidence of Continental Drift According to Wegner, the continents are sections of a past super continent called Pangea, which broke apart and drifted to their present locations.

As the sea floor spreads, the lava cools according to the magnetic poles at the time. The rocks on the ocean floor have proved that the earth’s magnetic field sometimes reverses. The inner core flips and so the north pole moves to the southern hemisphere! The earth itself does not flip.

Extinct Life Forms Preserved in the Geologic Record tell a story Evidence for Continental Drift: Fossils

Notice how fossils lined up across continents!

Evidence for Continental Drift: Rock Record

Sea Floor Spreading

Age of the Sea Floor

Evidence for the Theory 1.Continental shelves seem to fit together 2.Rock units and mountain ranges fit Pangaea 3.Fossil types fit Pangaea 4.Ocean research uncovered sea floor spreading 5.Radio-geology allowed us to date the age of rocks 6.Polarity of Rocks-Magnetic Evidence

What causes plates to move? Convection Currents- hot magma rises, cool magma sinks (like a lava lamp)

Con’t: How do plates move?

Movement of plates is caused by thermal convection of the “plastic” rocks of the asthenosphere which drag along the overlying lithospheric plates.

What are the three types of boundaries? Convergent – plates move toward one another Divergent – plates move away from each other Transform – plate moves sideways from each other

Convergent Boundaries A convergent boundary is created when two plates push towards each other.

Convergent Plates Three Types: 1.Continental/Oceanic 2.Oceanic/Oceanic 3.Continental/ Continental

Continental crust to continental crust collision Before collision After collision India-Asia (Himalayas) from:

Himalayas Continental - Continental The Himalayas were formed by the converging of the Eurasian plate and the Indian plate.

The Himalayas, the highest mountains in the world, were created this way. (In fact, they're still growing.) So were the European Alps. Even the Appalachian Mountains formed when two land masses came together. Collisional Ranges

ction Plate Subduction Because one plate gets pushed under another, it is called subduction. This is where volcanoes form!

Oceanic crust colliding with Continental crust

Java Trench Oceanic – Continental The Java trench is a convergence of the India plate on the southwest and the Burma and Sunda plates on the northeast

Continental and Oceanic Plates The only subduction zone in the Atlantic

Oceanic crust colliding with Oceanic crust

Philippine Plate Oceanic – Oceanic: The Philippine plate converges with the Pacific plate to form the Marianas Trench.

Divergent Boundaries A divergent boundary is created when two plates move apart from one another. Continental/Continental

Divergent Plates: Oceanic/Oceanic Example: Sea Floor Spreading

Mid-Ocean Ridge

Did you know that the Earth’s longest mountain range is underwater and is called the mid-ocean ridge? The Mid-Ocean Ridge system, shown above snaking its way between the continents, is more than 56,000 kilometers (35,000 mi) long. It circles the earth like the stitching on a baseball!

The Mid-Atlantic ridge is the most famous divergent plate boundary. The ridge is spreading at a rate of 3.5 cm/year

The S. W. Indian Ocean Ridge separates the Somalia and African plates from the Antarctic plate. It spreads at a rate of 1.5 cm/year South West Indian Ocean Ridge

Transform Boundaries A transform boundary is created when two plates slide past each other. Earthquakes are commonly made when the two plates build up stress and suddenly release it.

Transform Plates

Transform Faults The San Andreas fault in southern California is a transform fault that connects the sea-floor spreading ridge of the Gulf of California with the spreading ridge off Oregon and Washington. If these plate motions continue, Baja will splinter off California.

slipping and sliding Los Angeles, located on the Pacific plate, is now 340 miles south of San Francisco, located on the North American plate. In 16 million years, the plates will have moved so much that Los Angeles will be north of San Francisco!

The Great Rift Valley The Great Rift Valley is widening, in the process causing many volcanic eruptions and earthquakes in the area.

Hawaii forms The vast majority of earthquakes and volcanic eruptions occur near plate boundaries, but there are some exceptions.

The Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary. Hot Spots: The Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary.

Ring of Fire

The eruption of the Krakatau volcano in 1883 produced one of the largest explosions on Earth in recorded time (VEI=6) and destroyed much of Krakatau island.

Tsunami

Tsunami victims

Japan has been building tsunami walls of up to 13.5 ft high in front of populated coastal areas. Early warning systems enable low-lying populated areas to evacuate.

Mantle plumes originate deep within the asthenosphere as molten rock which rises and melts through the lithospheric plate forming a large volcanic mass at a “hot spot”.