Presentation on theme: "Physical Geography: Landforms. Overview Geologic Time Movements of the Continents Earth Materials Tectonic Forces Weathering and Erosion Processes Erosional."— Presentation transcript:
Physical Geography: Landforms
Overview 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 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 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