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.