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1) Earth’s internal heat engine.
2) Earth’s magnetic field.
3) Intro. to Seismology: Tools for seeing into the Earth’s interior.
(Chaps. 2-4)
TODAY’s LECTURE:
Convection in the Mantle Drives Plate Tectonics! But how?
3 reasons for internal heat:
Earth’s internal heat engineEarth’s internal heat engine
1) from impact during Earth formation 2) radioactive decay of uranium, thorium, potassium
3) heat released as inner core forms
Ways to transfer heat:
1) conduction - motion of atoms
2) convection - mass movement of material
Density:
Defined as the mass of a material, per unit volume.
Usually given in grams per cubic centimeter (g/cm3).
For comparison, the density of water is 1.0 g /cm3
.
Earth’s internal heat engineEarth’s internal heat engine
Hot materials are less dense and rise.Cooler materials are denser and sink.
Convecting materials in the Earth’s mantle originate deep, near the core-mantle boundary
Most heat from the deep interior is transferred to the shallow mantle by buoyant masses of
hot, low density material called “plumes”.
Hawaiian Islands
Plumes Create Volcanic Hotspots
Earth’s internal heat engineEarth’s internal heat engine
Cold down-goingmaterial
Hot upwellingMaterial
.
See: MantleUpwelling.MOV
See: MantleDownwelling.MOV
Earth’s internal heat engineEarth’s internal heat engine
See: MantleConvection.MOV
Heat of the upper mantle sets up shallowHeat of the upper mantle sets up shallowconvection cells that drive plate motions.convection cells that drive plate motions.
There are Three Basic Plate Margin Types: Can You Identify Them?
See Video:EarthOceanFloors.MOV
Consequences of Plate Motions: Mountain Building
Volcanic Activity
Mt. Mayon, Philippines
Consequences of Plate Motions: Earthquakes!
Convection Also Drives Deep Seafloor Hydrothermal Systems
The magnetic field is generated by an organized flow of electrons in the molten outer core.
Earth’s magnetic field:Earth’s magnetic field:
Earth’s magnetic field is a dipole with north and south Earth’s magnetic field is a dipole with north and south ends of opposing polarity. The magnetic poles and ends of opposing polarity. The magnetic poles and geographic (rotational) pole are offset by 23.5geographic (rotational) pole are offset by 23.500
Earth-Sun Interactions:(See: Bio_North_America.MOV
& Aurora.Mov)
Earth’s Earth’s magnetic magnetic field:field:
Lines of Lines of magnetic magnetic force are force are ~parallel to ~parallel to the Earth’s the Earth’s surface at surface at the equator, the equator, but are but are vertically at vertically at the poles.the poles.
Earth’s magnetic fieldEarth’s magnetic field
Naturally-occurring magnetic mineral
grains, like the mineral magnetite,
act as tiny bar magnets and become
oriented parallel to the field lines of the Earth’s magnetic field
Moon:
No magnetic field.
No molten outer core.
MARS: Had a magnetic field early in its history, but not today. How do we know? Remnant magnetism!
Magnetic Reversals:Magnetic Reversals:
Earth’s magnetic field reverses its polarity on an Earth’s magnetic field reverses its polarity on an irregular time scale of a few tens of thousand to irregular time scale of a few tens of thousand to hundreds of thousands of years. hundreds of thousands of years. (see MagFieldRev.MOV)(see MagFieldRev.MOV)
Magnetic reversals are recorded in igneous Magnetic reversals are recorded in igneous rocks by the remnant field orientations rocks by the remnant field orientations frozen into by the magnetic minerals (e.g. frozen into by the magnetic minerals (e.g. magnetite) that crystallize from magma as magnetite) that crystallize from magma as it cools.it cools.
Magnetic reversals can be dated!Magnetic reversals can be dated!
This is accomplished by using radiometric dating This is accomplished by using radiometric dating methods to date igneous rocks that preserve the methods to date igneous rocks that preserve the
remnant magnetism.remnant magnetism.