Chapter 5 Flashcards
1
Q
Sir Francis Bacon
A
noted that shorelines of the Americas “fit” those of Africa and Europe (late 1600s, early 1700s)
2
Q
Antonio Snider-Pellegrini
A
- proposed that all continents were once connected but catastrophically separated in the past
- thought the mechanism by which this occurred was Noah’s flood
- published book in 1859
3
Q
Alfred Wegener
A
- meteorologist and geophysicist
- studied glaciers
- continental drift
- Pangaea
4
Q
Continental drift
A
- 1915
- slow and gradual movement of continent over eons and eons of time
5
Q
scientific revolution
A
profound reversal of ideas
6
Q
Pangaea
A
“all land” -for a supercontinent whose breakup results in all current continents
7
Q
Wegener’s Lines of Evidence
A
- “Fit” of continents
- matching geology of continents
- fossil distribution
- living organisms distribution
- ancient climate
8
Q
fit of continents evidence
A
especially South America and Africa
9
Q
matching geology of continents evidence
A
especially with mountain chains
10
Q
fossil distribution
A
-similar fossils found on continents now separated by oceans
11
Q
good candidates for fossils
A
-terrestrian-meosaurus (reptile) and glossopteris (plant)
12
Q
living organisms distribution
A
-marsupials in South America and Australia
13
Q
ancient climate
A
evidence of glaciers in rock record at places that today could not make/sustain glaciers
14
Q
Sir Edward Bullard and 2 associates constructed a map that what?
A
pieced together the edges of the continental shelves of South America and Africa at depths of 900 meters
15
Q
glossopteris fossils were found where?
A
-Africa, Australia, India, South America, and Antarctica
16
Q
when did Wegener’s proposal attract criticism?
A
1924 when it was translated into English, French, Spanish and Russian
17
Q
main problem with continental drift
A
no mechanism to move the continents-doesn’t explain Rocky Mountains. in all only explains 1/3 of geology
18
Q
1960s
A
declassified Navy data seafloor
19
Q
big discovery
A
mid-ocean ridge
20
Q
how was mid-ocean ridge discovered?
A
sonar
21
Q
dredging of ocean floor revealed 2 patterns
A
1) sediments were thickest near continent and thiner near mid-ocean ridge
2) sediments near continents were young and old types, but those near the mid-ocean ridge were only young
22
Q
seafloor spreading
A
occurs at the mid-ocean ridge (divergent boundary)
23
Q
lithosphere
A
uppermost mantle and crust behave as a strong rigid layer
24
Q
plates
A
segments of lithosphere
25
where is lithosphere thinnest?
oceans
26
asthenosphere
weak region in mantle underneath lithosphere
27
tectonic plates
- aka lithospheric plates
- 20 segments
- in constant motion with respect to one another
28
largest plate
Pacific plate
29
plates that account for 94% of Earth's surface area
North American, South American, Pacific, Eurasian, Australian-Indian, Antarctic
30
as plates move the distance between 2 locations on different plates ____ _____ whereas the distance between sites on the same plate remains ____ _____.
gradually changes; relatively constant
31
most major interactions among plates occurs on their
boundaries
32
plate tectonics=
continental drift + seafloor spreading
33
The earth's surface is composed of
mobile plates (lithosphere)
34
divergent boundaries
- aka constructive plate margins
- aka spreading centers
- where new crust is made
35
2 locations divergent boundaries are prominent
1) Mid-ocean ridges
| 2) Continental Rift Valley
36
example of continental rift valley
east african rift
37
oceanic ridges
elevated areas of the seafloor that are characterized by high heat flow and volcanism
38
how much of earth's surface do oceanic ridges account for?
20%
39
seafloor spreading
the mechanism that operates along the oceanic ridge to create new seafloor
40
primary reason for elevated position of oceanic ridge
newly created oceanic crust is hot, making it less dense than cooler rocks found away from the ridge axis
41
cooling ___ hot material directly below oceanic crust, adding to plate's _____
strengthens, thickness
42
continental rifting occurs where
opposing tectonic forces act to pull lithosphere apart
43
convergent boundaries
- aka destructive plate margins
| - aka subduction zones
44
oceanic lithosphere is ____ ____ than the athenosphere
more dense
45
continental lithosphere is ___ ___ and resists _______
less dense, subduction
46
deep ocean trenches
surface manifestations produced as oceanic lithosphere descends into the mantle
47
angle at which oceanic lithosphere descends depends on its
density
48
as oceanic lithosphere ages, it
thickens and increases in density
49
oceanic-continental convergence
leading edge of plate caped with continental crust converges with a slab of oceanic lithosphere
50
sediments and oceanic crust contain a large amount of
water that is carried to great depths by a subducting plate
51
partial melting
the wedge of mantle rock is sufficiently hot that the introduction of water from the slab below leads to some melting
52
examples of oceanic-continental convergence
South America (Andes), Pacific NW (Cascade Mountains)
53
oceanic-oceanic convergence
2 oceanic slabs converge, one descends beneath the other, initiating volcanic activity by the same mechanism that operates at all subduction zones
54
examples of oceanic-oceanic convergence
Japan, Philippines, Middle Earth
55
continental-continental convergence
one landmass moves toward the margin of another because of subduction of the intervening seafloor
56
examples of continental-continental convergence
Himalayan, past Appalachians
57
subduction
sinking of ocean crust into the mantle
58
transform boundaries
- aka fault boundaries
- plates slide past one another
- near MOR's
59
ex. transform boundaries
San Andreas Fault
60
fracture zones
include active and inactive transform faults
61
where do active transform faults lie?
between 2 offset ridge segments, defined by weak, shallow earth quakes
62
transform faults provide
means by which oceanic crust created at ridge crests can be transported to a site of destruction
63
hot spots
a stationary plume of magma sourced from the lower mantle. Plates move over top of the hot spot.
64
examples of hot spots
Hawaii and Yellowstone National Park
65
new plate boundaries can be created or destroyed in response to
changes in the forces acting on the lithosphere
66
mantle plume
cylindrically shaped upwelling of hot rock (like beneath island of Hawaii)
67
hot-spot track
a chain of volcanic structures
68
paleomagnetism
the record of Earth's magnetic field as known via rocks
| -helps settle out polar wander and magnetic
69
some naturally occuring minerals are magnetic and hence
are influenced by Earth's magnetic field (ex. magnetite which is abundant in lava flows of basaltic composition)
70
Curie point
threshold for magnetism
71
polar wandering
idea that magnetic poles migrated
72
If the magnetic poles remain stationary, their apparent movement is produced by
continental drift
73
normal polarity
when rocks exhibit the smae magnetism as the present magnetic field
74
reverse polarity
when rocks exhibit the opposite magnetism are said to have reverse polarity
75
chrons
major divisions of magnetic time scale
76
magnetometers
used to do magnetic surveys of the ocean floor
77
high-intensity magnetism
regions where paleomagnetism of the ocean crust exhibits normal polarity that enhance Earth's magnetic field
78
low-intensity magnetism
regions where the ocean crust is polarized in the reverse direction and weaken the magnetic field
79
simplest type of convection
- analogous to heating a pot of water on a stove
- heating base causes material to rise in thin sheets that spread out at the surface and cool
- surface layer thickens and sinks to bottom until it reheats again
80
mantle convection
- more complex than simple convection
- mantle shape is spherical with a larger upper boundary than lower boundary
- driven by combination of 3 thermal processes
81
3 thermal processes that drive mantle convection
1-heating at the bottom by heat loss from Earth's core
2-heating from within by decay of radioactive isotopes
3-cooling from the top that creates thick, cold lithospheric slabs that sink into the mantle
82
what researchers agree on concerning convection
1-connective flow in the rocky mantle is the underlying driving force for plate movement
2-mantle convection and plate tectonics are part of the same system
3-convective flow in the mantle is the primary mechanism for transporting heat away from Earth's interior to the surface where it is eventually radiated into space
83
driving forces sof plate motion
- subduction of cold, dense slabs of oceanic lithosphere (aka slab pull)
- ridge push that results from elevated position of oceanic ridge and causes lithosphere to slide donwn the flanks of the ridge
- mantle drag-when flow in athenosphere is moving at a velocity that exceeds that of the plate
84
any acceptable model for plate-mantle convection
must explain compositional variations know to exist in the mantle
85
types of plate-mantle convection
-layering and whole-mantle convection
86
layering
2 zones, thin dynamic layer in upper mantle and thick sluggish layer underneath
87
whole-mantle convection
cold oceanic lithosphere sinks to great depths and stirs the entire mantle
-predicted that this type would cause entire mantle to completely mix which would eliminate chemically distinct magma sources
88
The unequal distribution of heat in Earth's interior generates
some type of thermal convection that ultimately drives plate-mantle motion
