Earth Sci 1. Study guide. CHAPTER 7

Continental drift, who proposed it, what was his hypothesis, and why rejected?

*CONTINENTAL DRIFT; a theory that originally proposed that the continents are rafted about. It has essentially been replaced by the plate tectonics theory. *ALFRED WAGNER proposed it. *Hypothesis said: -Pangea "supercontinent" began breaking apart 200 million years ago. -Continents "drifted" to present positions. -Continents "broke" through the ocean crust. *Rejected due to inability to provide a valid mechanism (his sun, moon, earth mechanism was not accepted).

What were some of the evidences used by Wegner to justify his hypothesis?

*Continental Jigsaw puzzle (Fit of South America and Africa), *Fossils match across the seas, *Rock types and Geologic features (structures match), *Ancient Climates.

Describe the 3 types of convergence, and characteristics of each

*OCEANIC-CONTINENTAL CONVERGENCE >>denser oceanic slab sinks into the asthenosphere. >>pockets of magma develop and rise >>continental volcanic arc forms *OCEANIC-OCEANIC CONVERGENCE >>two oceanic slabs converge and one descends beneath the other >>often form volcanoes on the ocean floor >>volcnic island arc forms as volcanos emerge from the sea. *CONTINENTAL-CONTINENTAL CONVERGENCE >>when subducting plates contain continental material, two continents collide >>can produce new mountains ranges such as the Himalayas.

What is the Curie Point and how does that relate to magnetism in rocks?

CURIE POINT: the temperature above which a material loses its magnetization (above 585* C). When Basaltic lavas erupt ar the surface at a temperature above the Curie Point the magnetite grains are non-magnetic. However, when the lava cools the iron-rich grains become magnetized and align themselves in the direction of the existing magnetic lines of force, then the mineral solidify and the magnetism possess "freeze" in this position which then becomes a Fossil Magnetism used to determine the position of the magnetic poles at the time of their formation.

What about ages and thickness of sea-floor sediment?

Deep sea drilling projects have gather samples of the ocean floor to establish its age. Finding supported the seafloor spreading hypothesis proving that the youngest oceanic crust would be found at the ridge crest and the oldest oceanic crust would be located adjacent to the continents. The thickness of ocean floor sediments provided additional verification of seafloor spreading. Revealing that sediments are almost entirely absent on the ridge crest and that sediment thickness increased with increasing distance from the ridge. (no seafloor with an age in excess of 180 million years was ever found).

What is the Earth's layers and what makes them different from each other?

Earth's three layers: crust, mantle and core can be further subdivided into zones based on physical properties, whether the layer is solid or liquid and how weak or strong it is. *OUTER CORE (solid iron), *INNER CORE (liquid iron), *LOWER MANTLE (solid rocky layer), *UPPER MANTLE >>Asthenosphere (weak solid) >>Lithosphere (rigid, solid) *CRUST (low-density rock) >>Oceanic >>Continental

What is a hot spot and where is a good example in the world?

HOT SPOT: a concentration of heat in the mantle capable of producing magma, which in turn extrudes onto Earth's surface (volcanoes can form over them). The intraplate volcanism that produced the Hawaiian Islands is one example.

Describe the lithospheres, the asthenosphere

LITHOSPHERE: The rigid outer layer of Earth, including the crust and upper mantle. ASTHENOSPHERE: A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 700 kilometers. The rock within this zone is easily deformed.

What was Pangaea?

Pangaea meaning "all lands" was the name Wegener used when referring to a single SUPERCONTINENT consisting of all Earth's landmasses once existed.

What are plate boundary types? Divergent, convergent, transform, what characterizes each one? What are some examples around the world of each type?

Plate boundaries were 1st established by plotting the locations of earthquakes and volcanos. Boundaries differentiate by the type of movement they exhibit. DIVERGENT BOUNDARY: (conservative margin) plates move apart creating new seafloor. ex: East Africa rift valleys CONVERGENT BOUNDARY: (destructive margin) plats move together, reabsorbed into the mantle. ex: The Peru-Chile trench along the west coast of South America. TRANSFORM BOUNDARY: (conservative margin) plates grind past each other without the production or destruction of lithosphere. ex: The San Andreas Fault.

*What is the sea-floor spreading hypothesis? How does it involve normal and reverse magnetic polarity?

SEAFLOOR SPREADING is the mechanism that operates along the oceanic ridges system to create new seafloor. Geophysicists learned that over periods of hundreds of thousands of years, Earth's magnetic field periodically reverses polarity. During a magnetic reversal the north magnetic pole becomes the south magnetic pole, and vice versa. When rocks exhibit the same magnetism as the present magnetic field, they are said to possess normal polarity, whereas rocks exhibiting the opposite magnetism are said to have reverse polarity.

What are subduction zones and what are deep ocean trenches? What is the driving force for horizontal plate motion?

SUBDUCTION ZONE: a long, narrow zone where one lithospheric plate descends beneath another. DEEP OCEAN TRENCH: An elongated depression in the seafloor produced by bending of oceanic crust during subduction. Ridge push is the driving force for horizontal plate motion. This gravity-driven mechanism results from the elevated position of the oceanic ridge, which causes slabs or lithosphere to "slide" down the flanks of the ridge.

What is the East African Rift zone, what happens there, what is the Red Sea, what is going on there?

The East African Rift Zone is an active continental rift and an excellent model of the initial stage in the breakup of a continent, where tensional forces have stretched and thinned the crust, allowing molten rock to ascend from the mantle. The Red Sea formed when the Arabian Peninsula split from Africa provides us with a view of how the Atlantic Ocean may have looked in its infancy. The Red Sea provides a view of what the split of the African continent (rift zone) will look like in the future.

How are the magnetic patterns on the sea floor configured? What do they look like?

The magnetic patterns are configured in: *HIGH-intensity magnetism, where NORMALly magnetized oceanic rocks enhance the existing magnetic field. *LOW-intensity magnetism, where the crost is polarized in the REVERSED direction which weakens the magnetic field. The magnetic pattern look like symmetrical stripes.

What role do mid-ocean ridges play with respect to the sea-floor spreading hypothesis?

The zigzag shape of the Mid-Atlantic Ridge roughly reflects the shape of the zone of rifting that produced the breakup of Pangaea. **brake up due to the Earth being a sphere (teacher comment).

What is the typical rate of sea-floor spreading?

Typical rates of spreading average around 5 centimeters (2 inches) per year. This is roughly the same rate at which human fingernails grow. Comparatively, slow spreading 2 centimeters per year and fast spreading 15 centimeters (6 inches) per year.