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Transcript
Bio 126 Introduction to Geology Overview • • • • What is Geology the Earth’s structure Geologic changes Internal process – Plate tectonics – Rock cycle • Rock types • External process – Erosion – Weathering – Soil formation • Geology is the study of the Earth, primarily by studying rocks • Rocks are aggregates of minerals • Minerals are naturally formed, solid, inorganic substances having specific chemical compositions and crystal structure Earth’s Layers- Core • At the center of the earth is the core that is divided into two parts: – Inner –Solid ball of iron and nickel about 1,490 miles thick – Outer – Molten of iron and nickel, about 1,430 miles thick Earth’s Layers- Outside Core are the Mantle layers: • Solid Mantle layer –lower mantle mostly solid about 1,740 miles thick • Outer Mantle divided into two layers – Asthenosphere - Outer molten layer of mantle is “plastic consistency” silicate materialcontinents float on this layer – Lithosphere- Rock layers that form surface of the earth – we walk on this layer • Outer-most solid layer of mantle material. • Crust material Earth’s Layers - Crust • Outermost solid very thin layer, floating on molten Asthenosphere mantle material • Oceanic Crust is thinner, only 3 miles thick • Continental Crust is thicker up to 12-40 miles thick • Cracks into Tectonic plates which bump into each other. These land movements we call Plate Tectonics, and cause earthquakes. Oceanic Crust Atmosphere Vegetation Biosphere and animals Soil Crust Rock Continental Crust Lithosphere Upper mantle Asthenosphere Lower mantle Core Mantle Crust (soil and rock) Biosphere Hydrosphere (living and dead (water) organisms) Lithosphere Atmosphere (crust, top of upper mantle) (air) Fig. 3-6, p. 54 Layers of the Earth 35 km (21 mi.) avg., 1,200˚C Crust 100 km (60 mi.) 200 km (120 mi.) Crust Low-velocity zone Mantle Lithosphere Solid 10 to 65km 2,900km 100 km (1,800 mi.) 3,700˚C Outer core (liquid) Core Asthenosphere (depth unknown) 200 km 5,200 km (3,100 mi.), 4,300˚C Inner core (solid) Fig. 10.2, p. 212 Volcanoes Abyssal hills Oceanic crust (lithosphere) Abyssal Oceanic floor ridge Abyssal floor Trench Folded mountain belt Abyssal plain Craton Continental shelf Continental slope Continental rise Continental crust (lithosphere) Mantle (lithosphere) Fig. 15-2, p. 336 Plate tectonics • The study of the deformation and movement of earth structures in semi rigid lithosphere. • Internal forces from the core create heat that keeps asthenosphere molten. It slowly flows. – Convection cells – Heated magma flows up, and cool near surface and moves back down. – Mantle Plumes bring hot magma towards surface like a fountain Convection Cell in Mantle Spreading center Collision between two continents Subduction zone Continental crust Oceanic crust Ocean trench Oceanic crust Continental crust Material cools Cold dense as it reaches material falls the outer back through mantle mantle Hot Mantle material convection rising cell through the mantle Two plates move towards each other. One is subducted back into the mantle on a falling convection current. Mantle Hot outer core Inner core Fig. 15-3, p. 337 Plate tectonicsDivergent Areas Lithosphere Asthenosphere Oceanic ridge at a divergent plate boundary • Plates spread apart in Divergent (constructive) areas forming new land as mantle material flows upwards. – Makes thinner Basalt Plate – Oceanic ridges still growing, as in Atlantic Ocean. – Rift valleys form on divergent land areas Fig. 10.6a Slide Convergent zones • • • • Plates move together and collide An Oceanic Plate sinks under Continental in a Subduction zone. – Along California, the Pacific Plate collides with and is is moving underneath North American Plate. – The Subducted Plate melts into asthenosphere convection cell, as it does molten rock moves up into crust of other plate. Lands uplifted, mountains (Sierras) form. Causes Earthquakes, volcanoes Continental plates collide neither subducts, both deform, mountains rise- Himalayas. Arc Island Chains • Some of the subducted plate material is scrapped onto the Continental plate. • Form while still off shore of continental plate • Forms Arc Islands • Japan • Arc Islands formed part of what became the North Coast ranges Trench Volcanic island arc Convergent plates Rising magma Subduction zone Lithosphere Asthenosphere Trench and volcanic island arc at a convergent plate boundary Fig. 10.6b, p. 215 Slide 8 Fracture zone Transform Faults Transform fault Lithosphere Asthenosphere Transform fault connecting two divergent plate boundaries • Plates in opposite directions in a fault • Run parallel to each, not colliding • Stresses as plates slip by each other cause earthquakes • Example: San Andreas Fault Fig. 10.6c, p. 215 Slide 9 Plate Tectonic Movements Plate Map Reykjanes Ridge EURASIAN PLATE JUAN DE FUCA PLATE CHINA SUBPLATE Transform fault PHILIPINE PLATE PACIFIC PLATE MidIndian Ocean Ridge Transform fault INDIAN-AUSTRLIAN PLATE Southeast Indian Ocean Ridge NORTH AMERICAN PLATE COCOS PLATE East Pacific Rise MidAtlantic Ocean Ridge EURASIAN PLATE ANATOLIAN PLATE CARIBBEAN PLATE ARABIAN PLATE AFRICAN PLATE SOUTH AMERICAN PLATE Carlsberg Ridge AFRICAN PLATE Transform fault Southwest Indian Ocean Ridge ANTARCTIC PLATE Convergent plate boundaries Plate motion at convergent plate boundaries Divergent ( ) and transform fault ( boundaries ) Plate motion at divergent plate boundaries Fig. 10.5b, p. 214 Slide 6 Earthquakes Liquefaction of recent sediments causes buildings of sink Two adjoining plates move laterally along the fault line Earth movements Cause flooding in Low-lying areas Landslides may occur on hilly ground Shock waves Epicenter Focus Fig. 10.9, p. 217 • • • • Slide 12 Abrupt movement along a fault line Energy move out in shock waves Focus is the point of initial movement Epicenter is location on surface above focus. Earthquake Faults • Strike – Slip faults move sideways – San Andreas • Dip-Slip faults move up / down motion – Uplifting mountains – Grabens form when an area drops down • Livermore Valley, Lake Tahoe “Richter Scale” Moment magnitude scale • • Magnitude of earthquake Measured on a seismograph Each unit has ten times greater the impact – 5.0 is 10x greater then a 4.0. Less than 4.0 4.0-4.9 insignificant 5.0-5.9 damaging 6.0-6.9 destructive 7.0-7.9 major Over 8.0 great minor The Ring Of Fire Volcanoes Earthquakes Fig. 10.5a, p. 214 Slide 5 Plate Map Reykjanes Ridge EURASIAN PLATE JUAN DE FUCA PLATE CHINA SUBPLATE Transform fault PHILIPINE PLATE PACIFIC PLATE MidIndian Ocean Ridge Transform fault INDIAN-AUSTRLIAN PLATE Southeast Indian Ocean Ridge NORTH AMERICAN PLATE COCOS PLATE East Pacific Rise MidAtlantic Ocean Ridge EURASIAN PLATE ANATOLIAN PLATE CARIBBEAN PLATE ARABIAN PLATE AFRICAN PLATE SOUTH AMERICAN PLATE Carlsberg Ridge AFRICAN PLATE Transform fault Southwest Indian Ocean Ridge ANTARCTIC PLATE Convergent plate boundaries Plate motion at convergent plate boundaries Divergent ( ) and transform fault ( boundaries ) Plate motion at divergent plate boundaries Fig. 10.5b, p. 214 Slide 6 Plate tectonics • Over time great movements of the continents have taken place. • Pangea formed when all the continents collide into one large land mass, about 250 Million years Ago • It then broke into Laurasia and Gondwanaland – 135 MYA – In recent Geologic time, Europe and North America Touched for a long time and we share many species • Current configuration only about 10 MYA – South and North America join recently with CA – Land bridge. Species still migrating across. History of Continental Drift Mountain Building Three Rock Types: • Igneous –unchanged cooled mantle material (Magma) • Sedimentary – weathered products of other rocks compacted together • Metamorphic – reworked rocks. Stressed by heat and pressure. Igneous Rocks Abyssal hills Abyssal Oceanic floor ridge Oceanic crust (lithosphere) • Plutonic or Intrusive Rocks form by cooling magma under earth’s surface. Abyssal floor Abyssal plain Pluton Mantle (lithosphere) Trench Folded mountain belt Craton Volcanoes Continental shelf Continental slope Continental crust (lithosphere) Mantle (lithosphere) Mantle (asthenosphere) – Ex. Granite – May be brought up in very large blocks called Batholiths such as the Sierra Nevada. These form as Plutons of new molten rock merge lower down in crust. • Volcanic or Extrusive Rocks cool rapidly at the earth’s surface. – Ex. Pumice, Lava Stone A Rock Crystals • Form as magma cools • Large crystals – form over a longer period of time – a slower cooling period – Form deeper down on crust - intrusive – Coarse grain rock with visible crystals granite • Volcanic activity has fastest cooling on surface - extrusive – Forms very fine grain crystals Sierra Granite Large Crystal sizes Sedimentary Rocks • Only 5% of crust, but make up 75% of rocks found on surface. • Laid down in layers or beds called Strata under water, then compacted. • Three types by origin of rock material: – Clastic (particles)– weathering of other rocks and deposition of debris – Chemical – precipitations in sea – Organic “Rock” Classification of sediments based on particle size Sediment Gravel Very Coarse Sand Coarse Sand Medium Sand Fine Sand Very Fine Sand Silt Clay Particle Size (mm) Larger than 2.0 2.0 – 1.0 1.0 – 0.5 0.5 – 0.25 0.25 – 0.10 0.10 – 0.05 0.05 – 0.002 Less than 0.002 Parent material (rock) Biological weathering (tree roots and lichens) Chemical weathering (water, acids, and gases) Particles of parent material Physical weathering (wind, rain, thermal expansion and contraction, water freezing) Fig. 15-6, p. 340 Sand 0.05–2 mm diameter Silt 0.002–0.05 mm diameter Water High permeability Clay less than 0.002 mm diameter Water Low permeability Fig. 3-25, p. 70 Clastic Sedimentary Rocks • Named by clastic (particle) size that makes up the framework of the rock • Smallest to largest particles: – Shale - Forms in Clay deposits – Siltstone – Forms in Still water – Sandstone – Forms in Slow moving water, marine seas, bays – Conglomerate – Gravel, pebbles & larger forms in high energy environments. – Breccia – angular rocks in conglomerate. • Smaller particles (clay & silt) travel farther, settle in low energy areas. Chemical Sedimentary Rocks • From from the precipitation of dissolved substances as water evaporates – Limestone – calcium carbonate in water • May also be biological (organic) – Halite – Salt dissolved in water and deposited as water evaporates. • Has be mined for years in areas. Leaves salt caves – Chert – Silica Dioxide:Flint, Jasper, Petrified Wood – Gypsum – Calcium Sulfate – Plaster, Alabaster Organic or Biological Sedimentary “Rocks” • Deposits of organic material, fossils • Not a true rock, not true minerals • Limestone- also may form as deposits of marine fossil skeletons & shells. – Most of organic material decomposed, oncemineralized part remains (Microscopic shells). • Coal – only partially decomposed, deposits of organic material – still energy rich. Metamorphic Rocks • Altered rocks • Formed by intense heat and pressure of being buried • Recrystallize to form new minerals • Often form layers perpendicular to direction of pressure – clue to mountain building events. Partial List of Metamorphic Rocks (* know these) Metamorphic Rock Original Rock Slate Shale Quartzite Quartz Sandstone Schist Slate Gneiss Granite Marble Limestone Serpentine Basalt, Grabbro Tectonic – Rock Cycle • New Rocks form from mantle material – Either as old plates melt into lower lithosphere and plutons of new rock rise up – Or as lava emerges from a volcano / vent • Sedimentary Rocks form from weathering & deposition • Metamorphic Rocks form as tectonic movements that only partially melt rocks The Rock Cycle Transportation Deposition Sedimentary Rock Slate, sandstone, limestone Erosion Heat, pressure, stress Weathering EXTERNAL PROCESSES INTERNAL PROCESSES Igneous Rock Granite, pumice, basalt Cooling Heat, pressure Magma (molten rock) Metamorphic Rock Slate, marble, quartzite Melting Fig. 10.8, p. 217 Erosion Transportation Weathering Deposition Igneous rock Granite, pumice, basalt Sedimentary rock Sandstone, limestone Heat, pressure Cooling Heat, pressure, stress Magma (molten rock) Melting Metamorphic rock Slate, marble, gneiss, quartzite Fig. 15-8, p. 343 Geologic changes • Internal processes – Heat from interior – Gravity • External processes – Erosion – Weathering • Chemical • Physical Soil forms from external processes • Erosion – Material is dissolved or worn away and moved by wind, water,etc. – Streams, rivers most important agents • Weathering loosens material from rocks – Mechanical – frost wedging. Water moves into crack, freezes and expands breaking off chips. – Chemical- water and acids, bases break down rock, very important in soil formation. It continues even under ground. External Processes and the Landscape Lake Tidal flat Glacier Spits Stream Lagoon Dunes Shallow marine environment Barrier islands Delta Dunes Beach Shallow marine environment Volcanic island Coral reef Continental shelf Continental slope Continental rise Abyssal plain Deep-sea fan Fig. 10.7, p. 216 Slide 10 • • • • • • • • Valleys Plains Marshes Deltas Lakes Dunes Beaches Bays Soil Composed of three components: • Eroded Parent Rock (dirt) – May determine special soils like serpentine – Broken down by weathering – the physical and chemical processes. • Organic Matter builds up as the remains of plants and animals living on the soil • Soil has an entire unique Living Microflora of bacteria, algae, fungi, and micro animals Soil Profile - Formation Oak tree Fern Word sorrel Lords and ladies Dog violet Earthworm Millipede Mole Honey fungus Grasses and small shrubs Organic debris Builds up Moss and lichen Rock fragments O horizon Leaf litter A horizon Topsoil Bedrock B horizon Subsoil Immature soil Regolith Young soil Pseudoscorpion C horizon Parent material Mite Nematode Actinomycetes Root system Mature soil Red earth mite Springtail Fungus Bacteria Fig. 10.12, p. 220 Soil Layers – or Horizons • O horizon – surface layer – Freshly fallen plant debris,animal wastes • A horizon – humus layer – Partially decomposed organic matter – Some inorganic minerals – Darker and looser (porous) than deeper layers • O & A layers essential for plant growth – Anchored by plant roots, trap nutrients – ALIVE !! Teams with micro flora, bacteria, fungi • C Horizon – parent Rock material Simplified Soil Food Chain Rove beetle Pseudoscorpion Flatworm Centipede Ant Ground beetle Mite Adult fly Roundworms Fly larvae Beetle Protozoa Mites Springtail Millipede Bacteria Sowbug Slug Fungi Actinomycetes Snail Mite Earthworms Organic debris Fig. 10.13, p. 221 Slide 16 Soil Conservation • Loss of O & A layers can doom agriculture • Tilling of soil increase erosion • Poor agricultural practice and drought made the Dust Bowl of 1930’s. • Soil Erosion Act passed congress in 1935 Kansas Colorado Dust Bowl Oklahoma New Mexico Texas MEXICO Fig. 10.20, p. 227 Slide 24 Areas of Soil Erosion Areas of serious concern Areas of some concern Stable or nonvegetative areas Fig. 10.19, p. 226 Desertification • • • • • • Loss of agriculture ability in dry areas. lose of top soil due to overgrazing Deforestation Tilling steep hillsides Soil compaction by machinery Salinization – irrigation water evaporates leaving a buildup of salts in soil – 35% of California crop lands suffer from levels of salinization Fig. 10.23, p. 229 Severe salinization in Colorado Slide 27 Desertification Moderate Severe Very Severe Fig. 10.21, p. 228 Stopping Soil Erosion • Terracing- making flat plateaus in hillsides – Good on steep slopes – Traditional form for rice in Bali, Andes etc. • Contour cropping –plowing rows with across slope. – Good on gentle slopes • Strip cropping alternate rows of crops – corn & alfalfa – One traps soil eroded by the food crop. • Agroforestry – several crops are planted together in rows between trees – Trees block wind, provide fruit, mulch, fuel • Terracing, contour planting, strip cropping, alley cropping, and windbreaks can reduce soil erosion. Figure 13-16