Download Plate Tectonics and the Earth`s Interior

Plate Tectonics and the Earth’s
Interior
Chapter 5

Crust

Mantle

Core

Earth’s Internal Structure
Thin
Cr u s t
– ocean basins
 ~ 3 miles
– mountain ranges
 ~ 30 miles

Deepest hole drilled
– About 7 miles
 Russia
Cr u s t

Constitutes less than 1% of Earth’s total mass

Average density
– 2.8 g/cm3

Crust ―floats‖ on mantle

Continents stand higher
– thick and less dense

Oceanic crust
– thin and more dense
Cr u s t
Oceanic Crust vs Continental Crust

Continental crust made of sial

Oceanic crust made of sima
– rocks containing silicon and aluminum
– e.g., granite
– rocks containing silicon and magnesium
– e.g., basalt
 Boundary
Mohorovicic Discontinuity
between the crust and the mantle
– 1 to 2 km thick
– seismic P-waves increase in velocity

1800 miles thick

Density

80% Earth’s volume
–
Mantle
4.5 g/cm3
Mantle

Mostly solid

Denser silicates rich in Mg and Fe
– olivine
Lithosphere
(Gk. stone shell)

~ 100 miles thick

Crust + Upper mantle
Asthenosphere

Part of upper mantle

Plastic layer
(Gk. weak shell)
– Completely liquid in places (magma)

18-60 miles thick
Mesosphere
(Gk. middle shell)

Solid dense mantle below asthenosphere
Core

~ 2000 miles thick

Density

Half the radius and one-third mass of Earth
–
11.0 g/cm3
Outer Core

Liquid

molten iron, nickel, cobalt, sulfur, or silicon

origin of Earth’s magnetic field
Inner Core

Solid (near melting point or partly molten)

Iron

8000° F

3 million atm
Plate Tectonics
Have the continents drifted?
Have the continents drifted?

Antonio Snider (1859) proposed the continents drifted
– Creationist
– Based his idea on Genesis 1:9-10
Genesis 1:9-10
9
And God said, Let the waters under the heaven be
gathered together unto one place, and let the dry land
appear: and it was so
 10 And God called the dry land Earth; and the gathering
together of the waters called he Seas: and God saw that it
was good.
Evidence?




The fit of the continents (taking into account the continental
shelves).
Correlation of fossil types across ocean basins.
A zebra-striped pattern of magnetic reversals parallel to mid-ocean
floor rifts, in the volcanic rock formed along the rifts, implying
seafloor spreading along the rifts.
Seismic observations interpreted as slabs of former ocean floor
now located inside the earth.
Continental Drift

Positional shifting of continents

Alfred L. Wegner
– German Geologist (1880-1930)

Pangaea
– ―all lands‖
– supercontinent
 The
Pangaea
Plate Tectonic Theory
earth's surface (lithosphere) consists of rigid plates,
each moving relative to adjacent plates. Deformation
occurs at the edges of the plates by three types of
horizontal motion:
– Divergence – plates moving apart
– Convergence – plates compressing together or one sliding under
the other (subduction)
– Transform –plates sliding past each other along a fault line
Earth’s plates
Theory of Plate Tectonics

Movement of plates explains:
– mountain formation
– earthquakes
– volcanoes

Divergent Boundaries
Occurs as the sea floor pulls apart at rifts or splits
– Mid-Atlantic Ridge
Convergent Boundaries

Occurs when one plate slides under another (subduction) or two plates collide
together
–
–
–
Pacific Plate beneath Japan
Cocos Plate beneath Central America
Indian-Australian plate colliding with Eurasian plate
Three Types of Convergent Boundaries
 Ocean-ocean
– two oceanic plates converge with one
subducting under the other
– Associated with island arcs (Aleutian Islands)
 Ocean-continent
– oceanic plate and continental plate
collide with oceanic plate subducting under continental
plate
– trenches and volcanic mountain chains (Sierra Nevada mountain
range)
 Continent-continent
―buckle‖
– No subduction
– two continental plates collide and
– Upfolded mountains (Appalachian Mountains and Himalayan
Mountains)
Transform Boundaries

Occurs where one plate slides horizontally past another
– San Andreas Fault (Pacific Plate slide against North American Plate)
Mid-Atlantic Ridge




20,000 feet below surface
~38,000 miles of ridges around globe (oceanic ridge)
divides Atlantic Ocean into two equal parts
At sea level, forms Iceland
Mid-Atlantic Ridge

Rift (trough) in middle of crest
– 20 miles wide

Submarine earthquakes under crest

Heat escaping rift

Iceland
ground cracks in Iceland are widening, often accompanied by
volcanic activity
– Between 1975 and 1984 there was a 23 feet separation
Mid-Atlantic Ridge
Satellite imagery
Interpretation of Observations of Mid-Atlantic
Ridge
 Magma
rises up at the rift forming new oceanic crust
– ―Younger‖ crust is at ridge and ―older‖ crust away from ridge
 Rocks
acquire magnetism as they cool
– Records earth’s magnetic field direction at time
– Continuous seafloor spreading should have a smooth magnetic
―tape recording‖ of reversals
Zebra stripe pattern
Problems for ―Slow and Gradual Plate Tectonics‖
 Zebra
stripe pattern has been confirmed
– Drilling in the basalt shows magnetic polarity changes in patches
down the holes with no consistent pattern with depth.
 Indicates rapid formation of basalt—not slow and gradual formation
 Magnetic
rapidly

reversals in lava have been shown to occur
Mid-Atlantic Ridge spreads about 2 inches per year
Is the present really the key to the
past?
Catastrophic Plate Tectonics
 Pre-flood supercontinent and dense ocean floor rocks
 Cold dense ocean floor sinks into softer, less dense mantle
– Edges sink faster due to friction and drag the rest of the floor
with it in conveyor belt fashion
 Faster
Catastrophic Plate Tectonics
movement creates more friction and heat in the
mantle, reducing its resistance, and making the mantle
move faster
– Runaway subduction
Catastrophic Plate Tectonics
 Mantle
material is displaced, causing large scale movement
through entire mantle
– Causes enough tension throughout earth to break up original
single land mass
 Hot,
mantle material rises up amid cracks and vaporizes
some ocean water causing geysers (Gen 7:11; Gen 8:2)
 Steam condenses in atmosphere to cause global rain (Gen
7:11-12)
 Rapid
Catastrophic Plate Tectonics
subduction of the cooler pre-flood ocean floor into
the mantle would have resulted in increased circulation of
viscous fluid (note: plastic, not molten) rock within the
mantle.
 accelerated convection in the core would cause rapid
geomagnetic reversals
– these would be erratic and locally patchy, laterally and at depth,
just as the data indicate
 Model
Catastrophic Plate Tectonics
provides mechanism for retreat of flood waters
(Psalm 104:6-8)
– Vertical earth movements at end of flood as opposed to
horizontal movements at beginning
 Plate
collisions would have pushed up mountains
– Slow movement would not be forceful enough to push up
Himalayans at Indian-Australian and Eurasian plates
6
Psalm 104:6-8
You covered it with the deep
as if it were a garment;
the waters stood above the mountains. 7 At Your rebuke
the waters fled;
at the sound of Your thunder they hurried away -
8 mountains rose and valleys sank -to the place You
established for them
 The
Final Summary
idea is quite new, and radical, and much work has yet
to be done to flesh out the details. There may even be
major modifications to the theory that increase its
explanatory power, or future discoveries could cause the
model to be abandoned. Such is the nature of scientific
progress. Scientific models come and go, "But the word of
the Lord endures forever" (1 Peter 1:25).
Future Consequences predicted by Plate
Tectonic Theory
 Portions
of California will separate from the rest of North
America
 The Italian ―boot‖ will disappear
 Australia will link to Asia
 Africa will separate from the Near East