Spring 2004
Lecture 8
Chapters 11
& 12
Know the progression of Era, Period and Epoch. We are in the Cenozoic Era, Quaternary Period
and Holocene Epoch
General principle of superposition: rock and sediment
arranged in layers from oldest to youngest- the study of this sequence is
stratigraphy.
Fundamental principle of earth science:
uniformitarianism assumes that the same physical processes active today were
active throughout geologic time. (versus catastrophism- a belief that the earth
was formed in a shorter sequence by huge, powerful events.)
Organization of materials from core to lithosphere is
due to gravity- iron towards that center and silica towards the surface.
Earth has 3 areas- Core, mantle and lithosphere
(crust). The fluid outer core generates
90% of Earth’s magnetic field. As it
rotates it generates electrical currents that induce magnetic fields.
Composition of continental (lighter, made of granite)
and ocean (denser, made of basalt) crust is different. The difference is the key to the concept of
drifting continents (when colliding, the denser ocean crust dives below
continental crust.) The crust is in a
constant state of adjustment (isostasy)
Geologic Cycle: Fueled by internal heat and solar
energy with the leveling force of gravity.
3 subsystems (hydrologic, rock and tectonic cycles) Rock cycle produces 3 rock types- igneous,
sedimentary and metamorphic.
Tectonic cycle brings heat energy and new material to
surface and recycles old. Crust (99%)
composed of 8 natural elements. Oxygen
and silicon account for 74.3% of crust.
Sedimentation driven by solar energy and gravity-
water is principal medium
Sea floor spreading produces new crust. Subduction is the collision of ocean floor
and continental crust (remelts, recycled as magma and rises again.) Both areas
are zones of earthquakes and volcanoes.
14 main plates in present crust.
Key
Terms (make sure know the ones in bold)
Geologic time
Lithoshpere
Isostasy
Endogenic (internal) system
Exogenic (external) system
Pangea
Divergent boundary (sea-floor
spreading)
Convergent boundary (collision zone)
Questions: 11 and 12
Definitions: endogenic system, continental drift and
plate tectonics
Tectonic processes deform, recycle and reshape
Earth’s crust.
Principal seismic and volcanic activity zones occur
along plate boundaries.
Crustal orders of relief: 1st (coarsest
landforms = continents and ocean basins), 2nd (intermediate level =
mountain masses, plains and lowlands) and 3rd (detailed relief =
mountains, cliffs, valleys, etc.)
Six orders of topographic regions: plains, high
tablelands, hills and low tablelands, mountains, widely spaced mountains and
depressions.
The oceans are much deeper than the continents are
high.
Endogenic processes result in
gradual uplift and new landforms.
Rock Stress: tension (streching), compression
(shortening) & shear (twist/tear)
Strain is how rocks respond to stress: folding
(bending- like pushing a cloth together on a table), or faulting
(breaking-earthquake)
3 types of convergent plate collisions that cause orogenisis:
oceanic plate-continental plate collision: Pacific
coast-
oceanic plate-oceanic plate collision:
continental plate-continental plate collision:
Himalayans
Two world mountain chains: Cordilleran System (
Crustal plates encounter friction as they slide
against each other. The overcoming of
this friction is an earthquake. Know focus (subsurface area along fault), epicenter (surface directly above
focus) and aftershock (waves
happening after main shock.)
Earth has 1300 volcanoes, less than 600 are active
and 50 erupt each year. A volcano is a formation at the end of a
central vent that rises from the asthenosphere through the crust arising as a
volcanic mountain. Lava, gases and
pyroclastics pass through the vent, to the surface and help build the volcanic
landform. They are a function of plate
tectonics and hot spots (page 331.)
Volcanic activity occurs in 3 areas:
1) along subduction boundaries (oceanic plate-continental plate or
oceanic plate-oceanic plate), 2) along sea-floor spreading centers and 3) at
hot spots.
Five volcanic landorms: cinder cone, caldera, shield
volcanoes, plateau basalts and composite volcanoes.
Geothermal energy is produced form magma which is
hot) heating groundwater which erupts as steam, geysers or thermal springs.
Key Terms
(make sure know the ones in bold)
Topography
Hypsometry
Craton (a nucleus)
Fault plane
Horst
Graben
Orogenisis
Seismograph
Richter Scale (Amplitude-magnitude
versus Moment-magnitude scale: be
familiar and the numbers and number per year: Table 12-1 on page 379.)
Questions: 3, 13 and 24
Definitions: Orogenisis and Composite volcano