PPllaattee TTeeccttoonniiccss aanndd tthhee EEaarrtthh’’ss IInntteerriioorr Chapter 5 Earth’’s Internal Structure Crust
Mantle
Core Crust Thin – ocean basins . ~ 3 miles
– mountain ranges . ~ 30 miles
Deepest hole drilled – About 7 miles . Russia Crust Constitutes less than 1% of Earth’’s total mass
Average density – 2.8 g/cm3
Crust Crust ―floats‖ on mantle
Continents stand higher – thick and less dense
Oceanic crust – thin and more dense
Oceanic Crust vs Continental Crust Continental crust made of sial – rocks containing silicon and aluminum – e.g., granite Oceanic crust made of sima – rocks containing silicon and magnesium – e.g., basalt Mohorovicic Discontinuity Boundary between the crust and the mantle – 1 to 2 km thick – seismic P-waves increase in velocity Mantle 1800 miles thick
Density – 4.5 g/cm3
80% Earth’’s volume Mantle Mostly solid
Denser silicates rich in Mg and Fe – olivine Lithosphere (Gk. stone shell) ~ 100 miles thick
Crust + Upper mantle Asthenosphere (Gk. weak shell) Part of upper mantle
Plastic layer – Completely liquid in places (magma) 18-60 miles thick Mesosphere (Gk. middle shell) Solid dense mantle below asthenosphere
Core ~ 2000 miles thick
Density – 11.0 g/cm3
Half the radius and one-third mass of Earth
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 PPllaattee TTeeccttoonniiccss Have the contiinents 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
Pangaea Plate Tectonic Theory The 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:
– 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 pllate and continental plate collide with oceanic plate subducting under continental plate – trenches and volcanic mountain chains (Sierra Nevada mountain range)
Continent-continent – two continental plates collide and ―buckle‖ – No subduction – 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 oceaniic 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 reversals in lava have been shown to occur rapidly
Mid-Atlantic Ridge spreads about 2 inches per year
IIss tthhee pprreesseenntt rreeaallllyy tthhee kkeeyy ttoo tthhee ppaasstt?? 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
Catastrophic Plate Tectonics Faster 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) Catastrophic Plate Tectonics Rapid 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 geomagnetiic reversals – these would be erratic and locally patchy, laterally and at depth, just as the data indicate Catastrophic Plate Tectonics Model 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
Psalm 104:6-8 6 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 Final Summary The 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