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Chapter 8
Earth Materials and Plate Tectonics
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface
The Geologic Timescale
4.5 billion years of Earth’s history
Divided into Eons, Eras, Periods
Source: USGS
Continents of the Past
Alfred Wegener proposed first fullscale scientific theory of the
breakup of one supercontinent
into multiple drifting continents
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•
•
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Pangaea: supercontinent
Intact about 300 million years ago
Outlines of continents fit across ocean
Tectonic structures match across
continents
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Fossil remains
Source: USGS
Earthquakes
Source: USGS
Magnetic Striping and Polar Reversals
Source: USGS
Continents of the Past
Satellite data show
rates of plate movement
from about 5 to 10 cm
(2-4 inches) per year
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Animation plate movement
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust
The Earth’s Interior
•Core: spherical central mass of the
Earth composed largely of iron; consists
of an outer liquid zone and an inner
solid zone
•Mantle: rock layer of the Earth beneath
the crust and surrounding the core.
•Crust: outermost solid layer of the
Earth, composed largely of silicate
minerals
• Oceanic crust: mafic rocks
• Continental crust: lower zone mafic
rock, upper zone felsic (less dense)
• Continental crust thicker than
oceanic
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Plates of the world
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface
The Lithosphere and Asthenosphere
Lithosphere: rigid outer shell of Earth, includes crust and upper mantle
Asthenosphere: plastic layer below the lithosphere
Lithospheric Plate: segment of lithosphere moving as a unit, in
contact with adjacent lithospheric plates along plate boundaries
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Plate Tectonics
Motion of lithospheric plates drives formation of Earth’s
mountains and other surface features.
Convergent
ocean-continental
ocean-ocean
continental-continental
Divergent
Transform
Plate Tectonics: theory of
tectonic activity dealing with
lithospheric plates and their
activity
Plate Tectonics
Subduction Tectonics
Denser plate subducts
Subduction: descent of the edge of a lithospheric plate
under an adjoining plate and into the asthenosphere
Source: USGS
Convergence
Source: USGS
Divergent
Source: USGS
Major Relief Features of the Earth’s Surface
Relief Features of the Ocean Basins
• Oceanic crust <60 million years old; continental crust >1 billion years old
• Ocean basins have:
• Midoceanic ridge
• Axial rift
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Transform Boundary
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Source: USGS
Hot Spot
Source: USGS
Rocks and Minerals of the Earth’s Crust
Igneous Rocks
Igneous rock: rock formed from the
cooling of magma
Magma: mobile, high-temperature
molten state of rock
• Intrusive Igneous rock: rock formed
from magma that solidifies below the
Earth’s surface
• Visible mineral crystals
• Extrusive igneous rock: rock formed
from magma that cooled rapidly at the
surface or under the ocean
• Mineral crystals microscopic
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tsunamis
http://www.nytimes.com/interacti
ve/2011/03/11/world/asia/mapsof-earthquake-and-tsunamidamage-injapan.html??smid=fbnytimes&WT.mc_id=WO-SM-EFB-SM-LIN-HSP-031411-NYTNA&WT.mc_ev=click
Source: USGS
Rocks and Minerals of the Earth’s Crust
The Earth’s Interior
• Most abundant elements in crust:
• Oxygen, silicon, aluminum, iron, calcium, sodium, potassium,
magnesium
• Minerals: naturally occurring inorganic crystalline chemical
compounds
• Rocks:
• Usually composed of 2 or more minerals
• Rock classes: igneous, sedimentary, metamorphic
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust
Igneous Rocks
Most composed of
silicate minerals:
contain silicon and
oxygen
• Felsic rock:
• Felsic minerals
• Light-colored
• Less dense
• Mafic rock:
• Mafic minerals
• Dark-colored
• More dense
• Ultramafic rock:
• Heavy mafic minerals
• Very dense
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust
Sediments and Sedimentary Rocks
Sedimentary Rock: rock formed from the accumulation of sediment
• Clastic—formed from rock and mineral fragments
• Chemically precipitated: formed by chemical precipitation from
seawater or salty inland lakes
• Organic: formed from organic material
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust
Sediments and Sedimentary Rocks
Sandstone,
deposited in
layers
Conglomerate
Shale
Chalk, a form of limestone
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust
Sediments and Sedimentary Rocks
Coal, a fossil fuel, is an organic sedimentary rock
Fossil Fuels: naturally
occurring hydrocarbon
compounds produced
from remains of organic
matter enclosed in
rock; examples are
coal, petroleum (crude
oil), and natural gas
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust
Metamorphic Rocks
Metamorphic Rock: rock altered in physical or chemical composition by heat,
pressure, or other processes taking place at a substantial depth below the
surface
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust
The Cycle of Rock Change
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.