Earth Systems ScienceChapter 7

I. Structure of the Earth

II. Plate Tectonics

The solid part of the earth system includes processes, just like the atmosphere and oceans. However, the time scales for processes in the solid earth are much longer. As a result, solid earth processes are important for climate over much longer time scales (e.g. millions of years).

Earth Systems ScienceChapter 7

I. Structure of the Earth

1. Seizmology, structure of the earth

2. The crust and lithosphere

3. The mantle

4. The core

Seismology: study of earthquakes and related phenomena

Earthquake: sudden release of energy resulting from the rapid movement between two blocks of rock

Body Waves

Surface Waves: like ocean surface

Seismology: study of earthquakes and related phenomena

Body Waves:

P-Waves

Primary waves

S-Waves

Secondary waves

Seismology: study of earthquakes and related phenomena

Surface Waves (similar to ocean waves):

Direction of wave movement

Direction of particle movement

Structure of the Earth

using seismology, the general structure of the earth can be determined

Moho

Moho: the boundary between the crust and the mantle

Upper mantle

Lower mantle

Metallic fluid

Metallic Solid

Structure of the Earth

http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml

The Crust and Lithosphere

• Continental crust: thicker, less dense, older20 km (weathered areas) to 75 km (younger areas) thick

• Oceanic crust: thinner, more dense, more recent~7km thick

• Lithosphere: the crust and uppermost (rigid) mantle

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This system is dynamic, not static!

The Crust and Lithosphere

The Mantle

• asthenosphere: The relatively plastic layer of the upper mantle of the Earth on which the tectonic plates of the lithosphere move; small fraction of molten material

• Upper mantle, lower mantle: upper differs from lower in seismic wave velocity, but not clear what causes the difference

• Composition of mantle is similar to carbonaceous chondrites, the original nebular composition, except depleted in volatiles and iron

• Where did the volatiles and the iron go?

The Core

• Mostly iron, ~6% nickel ~8-10% other materials

• More dense than the mantle

• Source of the earth’s magnetic field

• When a metal (conductor of electricity) undergoes convection, a magnetic field is created

• Over geologic time the polarity of the magnetic field shifts back and forth (North becomes South, and vice versa)

II. Plate Tectonics

1. Sea Floor Spreading

2. Continental Drift

3. Plate Tectonics

4. Deep Earth Processes

5. The Rock Cycle

Sea floor spreading: ocean topography

Sea floor spreading: magnetic polarity and age

Sea floor spreading: magnetic polarity and age

Sea floor spreading: magnetic polarity and age

Pangea

Continental Drift and Pangea

Plate Tectonics: plates and plate boundaries

Periods of statis (stress builds up between plates)Periods of movement (stress is released, earthquakes)

Plate Tectonics: plates and plate boundaries

Periods of statis (stress builds up between plates)Periods of movement (stress is released, earthquakes)

Plate Tectonics: plates and plate boundaries

Periods of statis (stress builds up between plates)Periods of movement (stress is released, earthquakes)

Plate Tectonics: plates and plate boundaries

Types of boundaries, or margins:

a) Divergent: plates moving away from each other

b) Convergent: plates moving towards each other

c) Transform: plates slipping past each other

Plate Tectonics: plates and plate boundaries

Plate Tectonics: plates and plate boundaries

Periods of statis (stress builds up between plates)Periods of movement (stress is released, earthquakes)

passive margin

transform margin

convergent margin

divergent margin

http://neic.usgs.gov/neis/plate_tectonics/plates.html

Plate Tectonics: plates and plate boundaries

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Deep Earth Processes

1. Heat

• Radioactive decay

• Gravitational energy released during accretion and formation of

earth

Deep Earth Processes

2. Mantle convection

Not sure exactly how the convection occurs

Deep Earth Processes

3. How they affect plate movement: Gravitational forces associated with density differences, due to hot less-dense magma from mantle

less densemore dense

The Rock Cycle: igneous rocks

• Rock Types: Igneous, sedimentary, metamorphic

• Igneous: cooling and solidification of magma that upwells from the mantle in mid-ocean ridges; all rocks originate from igneous

• Ocean lithosphere: average age 80 M yrs; max age 200 M yrs

• Continental lithosphere: max age 4 B yrs; parts of the continent that became tectonically dormant and now reside in the middle of continents, called cratons

• Why is the maximum age of the ocean crust so much less than the maximum age of the continental crust?

The Rock Cycle: cratons

• Weathering: decomposition of exposed rocks into finer material called sediments and dissolved into water

• Weathering caused by physical, biological, and chemical forces

• Erosion: transport of sediments and dissolved material by wind, landslides, and streams to basins in the ocean or on land

• Erosion forms landscapes: more resistant material is not eroded, leaving landforms such as peaks and ridges

The Rock Cycle: weathering, erosion, & sediments

• Sediments overly much of the oceanic and continental crust. Ocean sediments: sediments that were washed in through rivers, as well as shells from plankton near the ocean surface, that settle through the water column and settle on the ocean floor.

Continental sediments: from weathering on mountains, sediments accumulate in low lying basins; also, largely from former ocean floors that were transported, exposed, and uplifted due to tectonic activity

• Sediments are deposited in layers, accumulating through time; as the depth increases, temperature and pressure increases

• Lithification: Sediments are compacted into sedimentary rocks

The Rock Cycle: sediments and sedimentary rocks

http://neic.usgs.gov/neis/plate_tectonics/plates.html

Plate Tectonics: plates and plate boundaries

• uplift: due to continental collisions, former low-lying surfaces are forced up creating mountains and plateaus

• As soon as higher areas are formed, weathering and erosion begins

• In general, higher mountain ranges are younger, having experienced less erosion

• Subduction: sediments deposited in subduction zones are transported into the earth’s mantle; igneous rocks that were never eroded also enter subduction zones

• Metamorphism: subducted material undergo intense heat and pressure, are transformed into magma in the upper mantle, eventually to re-surface through mid-ocean ridges

The Rock Cycle: uplift, subduction, and metamorphism

The Rock Cycle

Kump et al. system diagram

The Rock Cycle

Mountains (all types)

Sedimentary Basinserosion,

sedimentation

Subduction Zone (all types)

subduction

Aesthenosphere (metamorphic)

metamorphism

Sea floor (igneous)

extrusion, volcanism

uplift

Frei system diagram

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