TODAY’s LECTURE: 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) Convection in the Mantle Drives Plate Tectonics! But how? Earth’s internal heat engine reasons for internal heat: 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 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” 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 Earth’s magnetic field: The magnetic field is generated by an organized flow of electrons in the molten outer core Earth’s magnetic field is a dipole with north and south ends of opposing polarity The magnetic poles and geographic (rotational) pole are offset by 23.50 Earth-Sun Interactions: (See: Bio_North_America.MOV & Aurora.Mov) Earth’s magnetic field: Lines of magnetic force are ~parallel to the Earth’s surface at the equator, but are vertically at the poles Earth’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 MARS: Had a magnetic field early in its history, but not today How we know? Remnant magnetism! Magnetic Reversals: Earth’s magnetic field reverses its polarity on an irregular time scale of a few tens of thousand to hundreds of thousands of years (see MagFieldRev.MOV) Magnetic reversals are recorded in igneous rocks by the remnant field orientations frozen into by the magnetic minerals (e.g magnetite) that crystallize from magma as it cools Magnetic reversals can be dated! This is accomplished by using radiometric dating methods to date igneous rocks that preserve the remnant magnetism [...]... flow of electrons in the molten outer core Earth’s magnetic field is a dipole with north and south ends of opposing polarity The magnetic poles and geographic (rotational) pole are offset by 23.50 Earth-Sun Interactions: (See: Bio_North_America.MOV & Aurora.Mov) Earth’s magnetic field: Lines of magnetic force are ~parallel to the Earth’s surface at the equator, but are vertically at the poles Earth’s... 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 MARS: Had a magnetic field early in its history, but not today How do we know? Remnant magnetism! Magnetic Reversals: Earth’s magnetic field reverses its polarity on an irregular time scale of a few tens of thousand to hundreds... Heat of the upper mantle sets up shallow 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 Earth’s magnetic field: The magnetic... years (see MagFieldRev.MOV) Magnetic reversals are recorded in igneous rocks by the remnant field orientations frozen into by the magnetic minerals (e.g magnetite) that crystallize from magma as it cools Magnetic reversals can be dated! This is accomplished by using radiometric dating methods to date igneous rocks that preserve the remnant magnetism