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Overview
• Geologic Time• Movements of the Continents• Earth Materials• Tectonic Forces• Weathering and Erosion Processes• Erosional Agents and Deposition
Geologic TimePretend the age of the earth (4.6+ billion years) is
compressed into one calendar year.
January 1 - Earth and planets formedEarly March - liquid water stands in pools.Late March - earliest lifeJuly - oxygen is important part of atmosphereOctober 25 – multi-cellular organismsLate November - plants and animals abundantDecember 15 to 25 - dinosaurs arise and disappear11:20 pm, December 31 - Humans appearOne 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.
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.
• Wegner’s evidence– Fit of continents– Fossil plants, animals, rock types /
geology • match on opposite shores• deposits inconsistent with current geography
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.
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
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
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
• General trends: temperature, density • Horizon composition, behavior
The Earth’s Interior
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 neck and dike: Shiprock, NM
Volcanic cones, obsidian flow: Mono Craters, CA
Volcanic Crater and Cinder Cone: Indonesia
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
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!
Gneiss (broad foliation)
Schist (narrow foliation)