Unit 10 Geology
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What interrelationships do plate tectonics explain?
The unifying theory of global dynamics. The lithosphere is believed to be broken into individual plates that move in response to convection.
What was basically proven (geologically) with the 1860's lying of the transatlantic telegraph cable?
The laying of the transatlantic telegraph cable 1860's proved that there was a mountain range in the middle of the Atlantic Ocean.
Alfred Wegener was famous for proposing which scientific theory?
He authored a book in which he carefully and systematically presented evidence for continental drift (1915).
What is "Pangea"?
The last ancient super-continent that included all of the today's major continental land masses.
Which two widely-separated mountain ranges formed a single range, millions of years ago?
If realigned, the Applachians and European Caledonian Mountains would form a single mountain chain of similar aged rock
Which geologic feature suggests that there was a continental glacier in Southern Pangaea?
This could be demonstrated by studying the ancient glacial striations remaining remaining from that glacier
Describe the biodiversity of plants and animals before 145 million years ago.
Similar plant and animal species within one large ecosystem will become rapidly dissimiliar from previously identical species when their ecosystem becomes isolated ecosystem from the large system.
Why might we not be able to match similar rocks on South America and Africa after 145 million years?
Coal and reptile fossils in Antartica imply that this land mass had been warm at one time. Thus Antarctica had been warm at one time. Thus Antarctica had been "drifting" from an area of warm climates to its current position.
Why was the Theory of Continental Drift rejected?
"Continental drift" theory was rejected because there was no acceptable method to move the continents.
Define and give a relative location with the following components of Earth's interior: lithosphere, asthenosphere, lower mantle, and the two core components of Earth.
- Lithospehere is the solid, strong and somewhat rigid outer layer that includes both the oceanic crustal rocks and the continental crustal rocks with a thin layer of mantle rock material this is "frozen" onto both of the (upper) visible crusts.
- Asthenosphere represents a plastic-like zone of partially-melted upper mantle rocks.
- Lower Mantle is the rocky zone between the asthenosphere and the liquid outer iron core.
- Liquid outer iron core is a mass of liquid iron (with minor amounts of other metal and rocks).
- Solid iron core has lots of theories as to the exact chemical composition of Earth's solid iron core.
What possibly is responsible for Earth's magnetic shield?
The solid iron core has been found to spin at a rate [2/3 second] faster than the rest of the planet. This spin difference generates a magnetic field or magnetic shield that encompasses the Earth.
What effect does Earth's magnetic shield have on our planet's life?
It is the magnetic shield that protects life on Earth from the effect of deadly readiation and cosmic rays that is generated by our sun and other stars. Without this shield, most life on Earth would disappear within a year.
What visible evidence (in the sky) is there for Earth's magnetic shield?
Visible evidence of Earth's magnetic shield is with the Northern Lights or the Aurora Borealis.
Describe what happens to a magnetite grain when it cools within a basaltic magma.
The can "align" themselves to the north and south magnetic poles that is present at the time of the grain formation.
The study of ancient magnetic fields, as preserved in the magnetic properties of certain rocks that contain magnetite.
What is a magnetic reversal and when may it occur again?
A complete 180 degree reversal of the polarity of Earth's magnetic field (North becomes South and vice versa). Magnetic reversal may occur at any time. These reversals have occurred more than 171 times on the Earth during the last 76 million years.
How often does our sun show magnetic reversals?
These spots on our Sun show reverse polarity (N-S) (or magnetic reversals) at 11 year cycles.
Where are the deep sea trenches located (in a tectonic environment)?
Deep trenches are found alongside continents and island arcs and not in the middle of the oceans.
What is the name and depth of the deepest submarine trench?
What theory did H. H. Hess propose in 1960?
He proposed the theory of seafloor spreading.
According to Dr. Hess, what would cause the seafloor to move symmetrically away from the ridge?
Mantle convection currents (caused by Earth's internal heat) will "carry" the seafloor crust symmetrically away from the mid-oceanic ridge.
According to Dr. Hess, what would happen to the seafloor away from a spreading center?
This seafloor crust will be pushed toward deep sea trenches or subduction zones where this crust eventually "descends" into the mantle zone.
According to Dr. Hess, how often would all of the ocean crust be regenerated?
The entire ocean floor crust should be regenerated every 200 million years (thus you should not find oceanic crust on the seafloor that is older).
What did Vine and Matthews discover that helped prove seafloor spreading?
They discovered a pattern of magnetic polarity stripes found within the oceanic crust that formed "parallel line of polarity" as they surveyed up and down the length of this ridge.
Describe how "magnetic polarity stripes" in conjunction with geomagnetic time scales are useful.
Can give an estimated age of the seafloor basalt.
Compare the ages of radioactive age dating of core of basalt at the oceanic ridge to the age basalt at the edge of the continents.
Radioactive age-dating of the oceanic basalt rock core was found to be youngest at the ocean's mountainous center and no more than 200 million years old at the ocean edges near the continents.
What is the significance of the oldest ocean sediments being younger than many surface rocks?
The oldest deep oceanic sediments called "oozes" are no more than 200 million years old. (It is estimated that this ooze generally accumulates at rate of 3 mm/1000 years).
Why is it that we no longer use the term "continental drift"?
Because all continents are attached to lithospheric plates which in turn are composed of both of oceanic crust and continental crust.
Describe the various crusts that makeup the North American plate (hint-oceanic and continental).
Most major plates contain both continental and oceanic crust (like the N. American plate).
Describe the permanence of the lithospheric plates.
Plates are not permanent features over geologic time. they can collide and join with other plates or they can spit apart and form "new" plates that move about the Earth.
What are the three major types of plate boundaries?
- Divergent plate boundaries
- Convergent plate boundaries
- Transform plate boundaries
What type of forces are associated with divergent zones (expansion or compression?)?
Forces of expansion.
What are two general types or classifications of divergent zones?
- Mid-oceanic ridge or spreading center
- Rift Valley (zone)
Where are most divergent zones located?
Oceanic divergent zones or spreading centers are located within ocean basin and involve only the oceanic crust. Rift valley's are found on land and on continental masses.
What happens to the oceanic crust above convection cell? (Remember convection)
Heated crustal rock is less dense than cold crustal rock. Thus the heated rock will rise above the surrounding area rocks. The rising of this crustal rock causes the crust to form large and long fractures (after all, rock is brittle and cannot be stretched).
Compare the height of the mid-oceanic ridge at a divergent center to the level of the abyssal plain.
This cold crust will sink by more than 10,000 feet (almost two miles) to create the oceanic abyssal plains that we find near the continental edges.
What is significant about life found around black smokers? (sun light?)
These smokers are hosts to large, exotic ecosystems that can exist without the effect of sunlight. Some have speculated that the Jupiter moon of Europa may also have black smokers similar to that on Earth.
Name an island nation directly over a spreading center or oceanic divergent zone.
Iceland is a landmass located directly over the mid-Atlantic spreading center.
What are continental rift zones?
Examples of "block faulting" that is caused by the stretching (extension and faulting) of the Earth's brittle continental crust.
What can happen (width) to a continent when it develops a large rift zone?
Rift zones actually make continent wider.
Name a famous American rift zone developed under a Texas bordering river.
The Rio Grande Rift of New Mexico
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