Flashcards in Quiz 6 Deck (47):
What is meant by the term “continental drift?”
Hypothesis/theory that continents move 1) relative to each other, and 2) relative to some “fixed reference point”
Who was an early proponent of the continental drift hypothesis?
What lines of evidence suggest that continental drift could have occurred?
1. Fit of the continents
2. Fit of the rock types in different continents
3. Distribution of terrestrial fossils
4. Fossil Assemblages as indicators of past glaciation
5. Location of regions with evidence for past glaciation
During the first half of the 20th century, what competing hypothesis was also invoked to explain the distribution of terrestrial fossils?
Land bridges have since subsided below sea level
why do apparent polar wander paths provide support for the Continental Drift Theory?
1. Glaciation scattered
2.No evidence for glaciation on continental areas that are now near the North Pole
3. Glaciated areas include portions of India and Africa that are now near the equator
The apparent position of a magnetic pole through time as determined from frocks from one locality but of different ages
Apparent polar water path
Location of dip needle pointed straight down?
Location of dip needle pointed straight up
Location of deep needle pointed horizontally
What does the angle of a dip needle mean?
The distance from the North Pole/magnetic field
Are magnetic poles at exactly the same places as geographic poles?
No, magnetic poles are near, but not quite the same place.
-North magnetic pole = 9 degrees away from the North geographic pole
How did we determine the direction of the earth’s magnetic field in the past?
-igneous rocks behaved as dip needles when they froze and dipped below as certain temp.
How do we know that the earth’s magnetic field has reversed itself many times in the past?
-igneous rocks have cooled in direction of old magnetic fields
-compasses that pointed south instead of north
A diagram that indicates when the earth’s magnetic field has normal polarity and when it had reverse polarity
Magnetic polarity time scale
What causes the earth’s magnetic field?
Iron composition in the earth’s core
What part of the earth’s interior is the source of the earth’s magnetic field? Why?
The core, because of the amount of iron.
A process whereby new ocean crust is produced by rising magmas underneath mid ocean ridges; crust on either side of a mid ocean ridge continually moves away from the ridge making room for the continuously produced new crust
Sea floor spreading
Evidence of sea floor spreading
Airborne magnetometers that were developed to detect submarines & for towing behind oceanographic vessels, allowing to determine the direction of magnetic remnance
How do we know the ages of the ocean floor near a mid-ocean ridge
Strip width as well as looking on magnetic reversal time scale
Pattern of magnetic stripes on both side of a mid-ocean ridge
-stripes of magnetically normal & magnetically reverses oceanic crust
-stripes parallel axes of mid-ocean ridges
Width of a particular strip on the sea floor depends on what two factors?
-length of time of a chron or subchron in the magnetic reversal time scale
Where would you expect to find the youngest oceanic crust?
Closer to the axis
What evidence suggests that the youngest oceanic crust is located closer to the axis?
Observation of increasing thickness of sediment on oceanic crust as you move away from the axis
Fastest mid-ocean ridge spreading
15 cm/year (East Pacific Ridge)
Slowest mid-ocean ridge spreading
2 cm/year (Mid-Atlantic Ridge)
What process causes melting under mid-ocean ridges?
A process whereby old ocean crust is pushed down into the mantle at trenches
3 main pieces of evidence of subduction
1. Ocean crust is being produced by sea floor spreading
2. the band of earthquake foci called the Benioff Zone, which angle down to the earth from trenches
3. The line of volcanos paralleling trenches
Why does melting occur under arcs?
Water mixes with magma crating reaction as plate subducts
Band of earthquake foci which angle down into the earth from trenches
A rigid portion of the lithosphere that forms a mid-ocean ridge and is destroyed at trenches; make up the whole lithosphere
Theory that describes and explains the creation and destruction of lithosphere plates and their movement over earth’s surface
3 main types of plate boundaries
1. Divergent boundary
2. Convergent boundary
3. Transform fault
Processes that occur along a divergent boundary
Plates move apart and new lithosphere is created (plate area increased)
Processes that occur along convergent boundaries
Plates come together and one plate is recycled into the mantle (plate area decreases)
Processes that occur along transform faults
Plates slide horizontally past each other (plate area doesn’t change)
What type of plate boundary produced the Himalayas?
What kind of crust is present on each side of the Himalayas?
What type of plate boundary produced the Andes?
What kind of crust is present on each side of the Andes?
Oceanic crust and continental crust
What type of plate boundary is the San Andreas Fault?
Strike-slip fault (transform)
Why do hot spots produce tracks of volcanos?
Hot plumes rise upward, forming volcanos on the overlying crust
Typical in solids, heat transferred atom to atom, no flow of atoms, relatively slow
Typical in fluids (gases and liquids), invokes flow of atoms carrying heat, relatively fast
Transfer of heat into space from glowing body
Ways to transfer heat