Transcript My PP Ch.22 Pt I

Structure of the Earth
Tectonics
Chapter 22
ISCI 2001
Crust
 (1). Thin, brittle
 Oceanic
 Basalt rock (dark); greater density
 Continental
 Granitic rock (lighter); less dense
 Less dense than mantle
 Floats
Mantle
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(1). Most of the volume (82%) and mass (65%)
– Thickest layer
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(2). Rich in Si and O
– Contains Fe, Mg, Ca (causes increased density)
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Density increased by weight of crust also
(3). Hotter than crust
– High pressure
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Caused by radio active decay of elements
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Flow of heat from core
(4). Regions – Upper Mantle
– Lithosphere
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Stiff, cool – similar to crust (forms one layer together)
– Asthenosphere
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Solid, plastic (solid flow)
(5). Upper Mantle
– Solid and rigid
– Plastic but not as much as upper mantle
Core
 Consist of:
 Metallic Fe
 2x dense as mantle
 (2). Inner Core
 Solid
 4000 to 7000 C
 Radioactive elements
 Earth development; matter hitting the surface
 Core sinking to the center
 (3). Outer Core
 Flows due to less pressure
 Rotation of Earth stirs up core material
 Produces magnetic field (flowing electrical charge)
Plate Tectonics
 (1). Continents sit atop of tectonic plates
 What are the plates made of?
 What is a continent?
 (2). Plates
 Consist of mantle and the crust (lithosphere)
 Plates move atop the asthenosphere (plastic)
 Continents move because they are embedded into the plates
 (3). Plate boundaries and continents
 Continents and plates do not have the same boundaries (overlapping) Figure
22.18
 A lot of action occurs at the plate boundaries!
Plates
How were the Plates Discovered?
 (1). Alfred Wegener
 Proposed the theory of “Continental Drift”
 Continents are in motion; drifting over geologic time
 Pangea (figure 22.8)
 Same fossils found in several different continents
 Matching rocks on both sides of Atlantic Ocean
 (2). Evidence for CD
 Seafloor Spreading
 Magnetic Stripes
Pangea
Evidence for Continental Drift –
Seafloor Spreading
 (1). Magma flows out of breaks in lithosphere
 New lithosphere is formed and old lithosphere will be recycled back
in trenches (22.16)
 Mid-ocean ridge
 Pushes the continents in specific directions
Evidence – Magnetic Stripes
 (1). Lava contains Fe and magnetite (Fe and O)
 Crystals are magnetic – line up with the magnetic field of the Earth
 Crystals point North and south / cool and freeze and become locked in
 Contains a record of the history of the magnetic field of the Earth
 Gives a striped, bar pattern (22.17)
 Alternates normal (today’s field) and reversed field from years ago.
 Runs along the spreading seafloor
How do the Plates Move?
 (1). As magma is heated deep in the Earth it moves upward
via convection currents (22.21)
 Hot rocks from lower mantle move upward cool in the upper
mantle and return
 Hit the lithosphere and can crack it – seafloor spreading
 Plates move atop ‘convection cells’