Earth Systems Science
Chapter 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 Science
Chapter 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
Surface Waves: like ocean surface
Earthquake: sudden
release of energy
resulting from the
rapid movement
between two blocks
of rock
Body
Waves
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: the boundary between the crust and the mantle
Moho
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, older
20 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
This system is dynamic, not static!
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml
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
Spinning globe with crustal ages
http://www.ngdc.noaa.gov/mgg/image/images.html#crustage
Continental Drift and Pangea
Pangea
Continental Drift
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml
Continental Drift
1) Begins with view of Earth with continents in their present positions, 2)
continents move back in time to reunite as Pangaea, 3) Pangaea label
appears, 4) Locations of stratigraphic and fossil evidence that Wegener used
to argue in favor of continental drift is added.
http://www2.nature.nps.gov/geology/usgsnps/animate/A14.gif
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
convergent
margin
transform
margin
divergent
margin
Plate Tectonics: plates and plate boundaries
http://neic.usgs.gov/neis/plate_tectonics/plates.html
Deep Earth Processes
1. Heat
• Radioactive
decay
• Gravitational
energy released
during accretion
and formation of
earth
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml
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 dense
more 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
The Rock Cycle: weathering, erosion, & sediments
•
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: sediments and sedimentary rocks
•
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
Plate Tectonics: plates and plate boundaries
http://neic.usgs.gov/neis/plate_tectonics/plates.html
The Rock Cycle: uplift, subduction, and metamorphism
•
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
Kump et al. system diagram
The Rock Cycle
http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Inside.shtml
1
Mountains
Sedimentary
(all types) erosion, Basins
5
sedimentation
uplift
Sea floor
(igneous)
Frei system diagram
4
extrusion, Aesthenosphere
volcanism (metamorphic)
2
subduction
Subduction Zone
(all types)
metamorphism
3