Module 2 Week 1 Geologic Cycles

Overview Endogenic and Exogenic Systems Geologic Cycle The Earth’s Interior Rock Cycle Tectonic Cycle (Plate Tectonics)

Endogenic and Exogenic Systems Exogenic systems are systems that are external to the earth Driven by insolation (solar radiation) Gives energy to air, water and ice, setting them in motion under the influence of gravity Example: Hydrologic Cycle Endogenic systems are systems internal to the earth Driven by heat from pressure and radioactive decay Fractures the earth’s surface, sets it in motion, builds mountains and triggers volcanoes and earthquakes Example: Tectonic Cycle

The Geologic Cycle The process by which landforms are shaped by balancing endogenic (building-up) and exogenic (wearing down) systems Interaction between hydrologic, tectonic, and rock cycles

Earth’s Internal Structure Opposition of gravity (inward pulling) and internal heating (outward pushing) Differentiation into alternating rigid and plastic layers

Inner core is solid iron possibly a single iron crystal Outer core is molten iron generates magnetic field geomagnetic reversals 9 in last 4 million years strength reduces to about 25% greater exposure to solar wind and high energy charged particles

Mantle Comprises 80% of Earth’s volume Composed of FeO, MgO, SiO 2 Rigid and Dense Increases with depth, pressure and temperature Gutenberg discontinuity separates Mantle from Outer Core Zone of transition density and velocity type of material

Upper Mantle Lithosphere Continental Crust “ sial” and granite Oceanic Crust “ sima” and basalt Mohorovi ĉ i ć (Moho) Discontinuity Boundary between crust and uppermost mantle Uppermost mantle Oxides and Silicates of Fe, Mg Asthenosphere: a region within the upper mantle 10% molten, unevenly distributed Additional heating from radioactive decay Convection currents create tectonic movement

Lithosphere is buoyant on the asthenosphere Free to move horizontally and vertically Horizontal motion expressed as plate tectonics Vertical motion expressed as isostasy Isostasy Vertical motion of lithosphere Crust exerts downward pressure on uppermost mantle and asthenosphere Exogenic processes redistribute the crust’s weight, changing downward pressure Results in isostatic rebound vertical motion of the crust does NOT contribute to horizontal tectonic motion

Rock Cycle Occurs where the earth’s crust comes into contact with exogenic processes Hydrologic cycle wind Original volcanic material of the crust becomes transformed into different rock types Tectonic cycle > molten mantle material > igneous rocks (e.g. basalt, granite) Hydrologic cycle > physical and chemical weathering of igneous rocks > sedimentation > deposition and compression > sedimentary rocks Tectonic cycle > sedimentary rocks become subducted, transform under heat and pressure to become metamorphic rocks Tectonic cycle > further subduction melts metamorphic rocks, available to become igneous again

Igneous Rocks Formed from magma Extruded as lava over the surface of the earth (Basalt) Intruded beneath the surface of the earth, erosion eventually reveals them (Granite) Plutons, Batholiths, Dikes, Laccoliths, Sills Most of the earth’s crust is made of igneous rocks Other rock types are produced through processes at the surface

Sedimentary Rocks Produced by: Sedimentation Weathering and erosion of any rock type to produce sediment Transportation and deposition of sediment Lithification Compaction, cementation, chemical actions Sediments deposited on bottoms of lakes or oceans Settle into horizontal layers or strata Stratigraphy Principle of Superposition Igneous intrusions typically appear within sedimentary strata. Erosion of these sedimentary layers reveals them Sandstone, shale (clay-sized particles), limestone (biotic – coral)

Metamorphic Rocks Any rock type, when exposed to extreme temperatures and pressure over millions of years can change form Metamorphic rocks can be formed by a variety of processes associated with subduction Compression from plate collisions Sheared and stressed along earthquake fault zones From weight of overlying materials during subduction Often found at the roots of mountains

Tectonic Cycle A function of the planet’s structure Occurs in the outermost layer of the planet Lithosphere and Upper mantle Driven by internal heating Gravitational compression Impact heating Radioactive decay Half-life

Geologic Time Uniformitarianism The same geological processes that operated in the past are operating in the present A time scale that measures the entire life of the planet 4.6 billion years old Eons, era, period, epoch Divisions typically based on fossil evidence Time system defined by interaction between biosphere and other spheres Often marked by mass extinctions Precambrian Eon Vast majority of earth’s history (roughly 4 billion years) Early period sees the first bacteria, photosynthesis and evolution of atmosphere End of period marked by formation of modern atmosphere

Tectonic motion occurs on the timescale of hundreds of millions of years Pangaea to present continental distribution: 248 million years Landform building processes associated with tectonic activities occur on a timescale of tens of million of years Orogeny: mountain building Current time period Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene epoch Geomorphologists take the late Quaternary Period, inclusive of the Holocene, as their period of study Separates physical geographers from geologists Humans are present during this period Holocene: 10,000 years ago, marks the rise of agriculture End of an Era? Possibly even an Eon? Mass extinction, atmospheric change

Plate Tectonics Two main factors: Buoyancy of Lithosphere on Asthenosphere Uneven heating and convection within Asthenosphere Results in: Fragmentation of Lithoshpere into mobile plates Places where the plates move away from each other Divergent plate boundaries or sea-floor spreading Places where plates move toward each other and collide Convergent plate boundaries or subduction zones Evidence Abraham Ortelius (1596), Francis Bacon (1620) noted “fit” of coastlines Alfred Wegener (1915) proposed the idea of drift Similarity in rocks and geographic features across continents Similarity of certain fossil species across continents

End of Precambrian Eon, beginning of Phanerozoic.

End of Paleozoic Era, beginning of Mesozoic

Early Cretaceous period, Mesozoic Era Opening of North Atlantic Ocean

End of Cretaceous Period and Mesozoic Era, beginning of Cenozoic Era Mass extinction of dinosaurs, rise of large mammals Asteroid or comet impact (in what is now the Yucatan Peninsula)? Opening of the South Atlantic Ocean

Divergent Plate Boundaries Occur where molten material from the Asthenosphere penetrate through the crust A form of volcanism Occur in the oceans because oceanic crust is thinner than continental crust Creates new crust Pushes plates apart (sea-floor spreading) Basalt (extrusive) Features Mid-oceanic ridges Fracture zone , Transform faults

Convergent Plate Boundaries Occurs where two plates collide One plate slips beneath the other Subduction (hence subduction zone ) Subducted plate passes back into asthenosphere Friction between plates melts rocks of the lithosphere Creates continental crust Granite (Intrusive) Features Orogenesis (mountain building) Oceanic trenches Volcanoes Earthquakes

Note: Subduction zones, especially ringing the Pacific Ocean

Note: association of volcanoes with subduction zones Note also: Hotspots

Hot spots Places in the crust away from plate boundaries where molten material from the asthenosphere punches through the crust Typically in oceanic crust Produces basalt The motion of the plate over the hot spot often creates chains of volcanic mountains Island chains (such as Hawaii) Mauna Loa in Hawaii is the world’s tallest mountain if measured from the ocean floor Seamounts

Module 2 Week 1 Geologic Cycles

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Module 2 Week 1 Geologic Cycles