Transcript What type? - El Camino College

Physical Geography:
Landforms
Overview
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Geologic Time
Movements of the Continents
Earth Materials
Tectonic Forces
Weathering and Erosion Processes
Erosional Agents and Deposition
Geologic Time
Pretend the age of the earth (4.6+ billion years) is compressed
into one calendar year.
January 1 - Earth and planets formed
Early March - liquid water stands in pools.
Late March - earliest life
July - oxygen is important part of atmosphere
October 25 – multi-cellular organisms
Late November - plants and animals abundant
December 15 to 25 - dinosaurs arise and
disappear
11:20 pm, December 31 - Humans appear
One second before midnight - Automobile
invented
What is ‘tectonics’?
• From Greek ‘tektonikus’
meaning building or construction
• Plate tectonics refers to the process of
earth crust formation, movement, and
destruction.
What is a ‘Plate?’
• Lithospheric plate: crust + upper
mantle
• Aesthenosphere: plastic mantle
History of Plate Tectonics
• ‘Fit’ of coastlines recognized early
– Sir Francis Bacon (1600s)
• No mechanism for motion
• 1915 Alfred Wegener
proposes theory of
continental drift.
• Supercontinent Pangaea (‘all-earth’) [225mya].
• Fragmentation and drift to current positions.
Plate
Movement
History
• Wegner’s evidence
– Fit of continents
– Fossil plants, animals, rock types / geology
• match on opposite shores
• deposits inconsistent with current geography
Striking Match of Geologic
Regions
Striking Match of Biological Regions
History of Plate Tectonics
• Problem with continental drift?
– No sound mechanism for the ‘drift’!
– Wegner hypothesizes spin of earth or tides…..
History of Plate Tectonics
• New theory for motion: Arthur Holmes
(1930s)
– thermal convective cells in the upper mantle
(aesthenosphere)
– theory is largely ignored
History of Plate Tectonics
• In the 1960s, Harry Hess and Robert Deitz
(geophysicists) propose sea floor spreading
along mid-oceanic ridges for plate motion.
Sea Floor Spreading
Plate Tectonics Theory
• Continental Drift + Sea Floor Spreading
+ new data  Theory of Plate Tectonics
Plate Tectonics Theory
• Plate boundaries: main location for
Earth’s volcanic and earthquake activity.
This is main place where mountains are
created.
• Type of plate boundary determines
activity.
• 3 types
– diverging (spreading)
– converging (colliding)
– transform (sliding past each other)
Geography of the Plates
• 7 major plates; several minor plates
• Small plates / boundaries still unknown
Plate Margins: how do we know?
• Marked by volcanic and tectonic activity
Convergent Plate Boundaries
• Activity:
– subduction; shallow to deep earthquakes;
volcanism (continental)
• Features:
– ocean trench; explosive volcanic mtns on
continental margin
Divergent Plate Boundaries
• Landscape features:
– land: rift valleys,
volcanic mountains,
thinning crust
– ocean/sea: rift
valleys, mountain
ranges
Divergent Plate Boundaries
• Examples:
– Atlantic Mid-Oceanic
Ridge
– Red Sea
– Rift valleys of eastern
Africa
The Rock Cycle
Earth Materials
• Formation of Earth
• Three major rock
types
– Igneous
– Sedimentary
– Metamorphic
Formation of the Earth’s Interior
• @5 bya, plantesimals (meterorites,icy
comets) collide  heat released
(Kinetic energy to thermal energy)
• Entire planet melts (still cooling today)
• Gravity sorts
materials by density
– Fe in center
– Si and O compounds
towards surface
The Earth’s Interior
• General trends: temperature, density
• Horizon composition, behavior
Distance: 6730 km (3963 miles)
Igneous Rocks
• Igneous (ignus = fire)
• Formed from the cooling of molten rock
(magma/lava), a process called
crystallization.
– Slow cooling  larger crystals > dense rock
– Rapid cooling  small crystals > lighter rock
• Two classes of igneous rocks
– intrusive: formed inside the Earth
– extrusive: formed at Earth’s surface
Igneous
Extrusive
Landscapes
Volcanic Crater and Cinder Cone: Indonesia
Volcanic cones, obsidian flow: Mono
Craters, CA
Volcanic neck and dike: Shiprock, NM
Igneous Extrusive Rocks
• Cools rapidly - exposed to surface
• No visible crystals
• Examples
- rhyolite
- andesite
-basalt
Some unique volcanic rock types
 Pumice
(vesicular)
- sometimes so
light it floats!
Obsidian 
– glassy, ‘curved’
fracturing
– used for
arrowheads by
Native Americans
Igneous Intrusive Rocks
• Cools slowly (thousands of years)
• Visible crystals
• Examples
- granite
Typical Igneous Intrusions
Exposed Batholiths
Sierra Nevada, CA
Sedimentary Rocks
Sedimentary
Rocks
Relative Abundance by
Type
Compaction
Cementing
Formation
Limestone (CaCO3)
Sandstone (larger grains)
Shale (fine grains)
Where do Sedimentary Rocks
Form?
Terrestrial
environments
(non-marine)
 Rivers and floodplains
(fluvial environment)
 Lakes
 Deserts (aeolian
environment)
Marine
environments
 Continental shelf
 Continental slope
and rise (deep sea
fans)
 Abyssal plain
 Beach and barrier
islands
Metamorphic Rocks
or That’s very Gneiss, but
I don’t give a Schist!
Schist (narrow foliation)
Gneiss (broad foliation)
Which Type?
Which Type?
Sedimentary - limestone and shale
What type?
Metamorphic
Amitsoq
What type? Gneiss, Greenland, 3.8 billion old
What type?
What type? Sedimentary - Sandstone in
Utah
What type?
What type? Extrusive Igneous Reunion Island, Indian Ocean
What type?
What type? Folded Sedimentary ‘Sheep Fold’, Wyoming
What type?
What type? Sedimentary - Vasquez
Rocks, Southern California
Morro Rock, CA
What type?
Devil’s Tower, Wyoming
Morro Rock, CA
What type? Intrusive Igneous
The Rock Cycle