Ch. 2 The Sea Floor Notes

Name____________________________________Date______________________Ch. 2 The Sea Floor NotesMrs. Pecksea floor geologically different from continentsgeological processes that occur beneath sea affect oceans and dry landhabitats (natural environments where organisms live) are shaped by geologicalprocesses, therefore, marine biologists are interested in geologyThe Water PlanetEarth is 4.5 billion yrs oldoceans cover 71% of earth's surfaceoceans imp in regulating our climate and atmosphereThe Geography of the Ocean Basins fig. 2.1Ocean classified into 4 basins:1. Pacific- deepest & largest2. Atlantic- 2nd largest3. Indian - just a little smaller than atlantic, similar depth4. Arctic - smallest & shallowestSeas: shallow and connected to oceansMediterranean Sea, Gulf of Mexico, South China Sea, Bering SeaCaribbean Sea, Baltic Sea, North Sea, Arabian Sea, Coral Seaworld ocean- a concept is used to indicate that all oceans on earth areinterconnected4 oceans are interconnected: seawater, materials and organisms may move from one ocean to anothersouthern ocean-the continuous body of water that surrounds Antarctica fig 2.2*the world ocean, which covers 71% of the planet, is divided into four major basins: the Pacific,Atlantic, Indian, and Arctic oceans.The Structure of the EarthEarth formed 4.5 billion yrs. ago from dust particles (from big bang) that collidedand formed bigger particles......and so on....building up earth & other planetsbig bang -theory that a cosmic explosion produced clouds of dust & gas fromwhich the earth and solar system originatedoccured ~ 15 billion yrs agodensity- the mass of a given volume of a substancemass- the amount of matter of a substancevolume- the amount of space a substance occupies

The Geography of the Ocean Basins 2The Structure of the EarthDensity is the mass of a substance per unit volume. Substances of low density willfloat on substances of higher density. density = mass / volumeAs the earth formed: earth was molten-densest mat. flowed toward center-lightest mat. floated toward the surface....cooled...formed thin crust-atmosphere formed & then oceans formedInternal Structurefig2.3concentric layers: formed according to materials densitycore- the innermost layer of earth, consisting of alloys of iron2 parts: 1. solid Inner core2. liquid Outer core- swirling motion of Fe forms earth’smagnetic fieldmantle- the semi-liquid region between the crust and coremostly solid, extremely hot.(melting pt of rock)...some actuallyflows slowly2 parts: 1. Lower Mantle- thick layer2. Upper Mantle- thinner layer2 parts- A. Asthenosphere- lower part ->flowingB. Lithosphere-towards surface->solidupper mantle & crustcrust- thin outermost solid layer of earthcomposition is diff. for crust of oceans & crust of continents2 types: 1. Oceanic Crust2. Continental CrustThe earth is composed of three main layers: the iron-rich core, the semiplasticmantle, and the thin outer crust.Continental and Oceanic Crustsmany physical and chemical differences b/w 2 crustsOceanic Crust Continental Crustmakes up sea floormore dense less densefloats lower on top of mantle floats higher on mantleconsists of basalt-dark-colored rock consists of granite-light-colored rock that formsthat forms the sea floor or oceanic crust most of the continental crustgeologically young (200 mya) geologically very old (3.8 billion yrs)

The Origin and Structure of the Ocean Basins 3Early Evidence of Continental Driftcoal deposits, geological formations, & fossils are similar on opposing coastsWegener: 1. proposed 1st hypothesis of Continental Drift fig. 2.4continental drift- the movement of continental masses on the surface of the earth2. coined Panagea-suggested that all continents once were joined intoa “supercontinent”Panagea-the single large landmass, or supercontinent, that broke up to formtoday’s continentsTheory of Plate Tectonicsplate tectonics-the process involved in the movement of large plates on the earth’scrustDiscovery of the Mid-ocean Ridgemid-ocean ridge-the continuous chain of volcanic submarine mountains thatextends around the earth. fig 2.5 , fig 2.6largest geological feature on earthsome submarine mountains reach surface to form islandseg. Iceland, Azores (east of spain)transform faults-large horizontal displacement in mid-ocean ridgecracks in earth’s crust along mid-ocean ridgeincludes 1. Mid-Atlantic Ridge- portion of mid-ocean ridge in thecenter of the Atlantic2. East Pacific Rise - portion of mid-ocean ridge in Pacificridge forms upside down Y extendingup eastern side of PacificThe mid-ocean ridge system is a continuous, submarine range of volcanic mountains that runsthrough all of the ocean basins.trenches- a narrow, deep depression in the sea floorcommon in Pacific

The Origin and Structure of the Ocean Basins 4Significance of the Mid-Ocean Ridge-many earthquakes and volcanoes are associated with Mid-Ocean Ridge-sediment-loose mat. (sand & mud) that settles on the bottomgets thicker moving away from ridge-as move away from ridge....the older the rocks & sediment-patterns of bands of rock that move away from ridge reveal a reversal in earth’smagnetic field every million yrs! fig 2.8 really cool stuff!!!magnetic anomalies- magnetic bands in the sea floor that run parallelto the mid-ocean ridge-the sea floor was not formed all at once but in strips that parallel the midoceanridgeEarthquakes and volcanoes are associated with the mid-ocean ridge. The sedimentsare thicker & the rock of the actual sea floor is older the farther they are from the ridge.Bands of rock alternating between normal & reversed magnetism parallel the ridge.Creation of the Sea Floor fig 2.9induction-the development of a generalized conclusion from a series ofisolated observationssea-floor spreading-the process by wh/ new sea floor is formed as itmoves away from spreading centers in mid-oceanic ridgessteps: 1. rift forms- a crack in earth’s crust formed as pieces of crust separate2. releases pressure in mantle ->hot mantle melts & rises thru rift3. ascending mantle mat. pushes up oceanic crust (around rift) formingmid-oceanic ridge4. molten mantle mat. cools & solidifies forming new oceanic crustpushing older crust further away from ridge5. process repeats->sea floor moves away from ridge creating new floor*this is why sediment gets thicker and rocks get older as moveaway from ridge*new sea floor created “freezes” the mag. field of that time,preserving that magnetization as it moves away from ridge.When earth’s mag. field reverses, a new “stripe” begins on floor

Sea-Floor Spreading & Plate Tectonics fig 2.10lithosphere-top rigid layer->crust & top part of mantle tht covers earth’s surfacemeans “rock sphere”“floats” on top of asthenospherebroken into lithospheric plates- plates that can contain continentalcrust, oceanic crust or bothasthenosphere-layer of upper mantle that lies below the lithospheredenser & more plastic(flowing-like) than lithospere*it is the slow swirling motion of asthenosphere tht drives motion oflithospheric platesearth’s surface is broken up into a # of plates. These plates, composed of crust & toppart of the mantle, make up the lithosphere. These plates are ~ 60 miles thick.The Origin and Structure of the Ocean BasinsSea-Floor Spreading & Plate Tectonics fig 2.11 & 2.12Plate Boundaries (3 types) ridges, trenches, shear boundary1. At Ridges:-at ridges lithospheric plates move apart (sea-floor spreading) and newoceanic lithosphere is formed.-if plate includes part of continental crust, then continent is moved away fromridge as plate moves away.........continental drift!-plates move b/w .8-7 inches apart a year!-*as new lithosphere is created at ridge.....old lithosphere is destroyed attrenches2. At Trenches:subduction-downward movement of a plate into the mantle thatoccurs in trenchessubduction zones- trenches where subduction occurs1. formed when 2 plates collide & one plate dips below the otherand sinks back down into the mantle2. plate sinks and breaks up in mantle causing earthquakes3. plate melts in mantle...some of molten rock rises to form volcanoes

The Origin and Structure of the Ocean Basins 6Sea-Floor Spreading & Plate Tectonics fig 2.11 & 2.12oceanic plate colliding with continent: oceanic plate always descends intomantle (bcs continental plate less denseand “floats” on topvery old rocks only found on continents bcsoceanic crust destroyed in trenchesdevelops continental volcanoesalong coastal mountain rangeseg. Andes on pacific coast of S. Am.oceanic plate colliding with oceanic plate: one plate dips below the other(either plate can be the one that dips)creates earthquakes and volcanoes-these volcanoes may rise to form chainsof volcanic islands called island arcs-a curvedchain of volcanic islands that form along a trencheg. Aleutian and Mariana islands fig2.13continental plate colliding w/ continental plate: both are “floating” so neitherwill sink or be subducted. Therefore notrench is formed and 2 plates become“welded” together....increase force causesrock/crust to buckle & fold like accordionforming mountain rangeseg. Himalayas (India & Asia collided)Plate Boundaries (3 types) ridges, trenches, shear boundary3. Shear Boundaries:shear boundary-boundary between 2 plates that move past each other on theearth’s surfacefault-a crack in the earth’s crust usually formed when two pieces of crust aremoving past each other-2 plates can slide past each other (neither creating or destroying lithosphere)-great friction between plates...they get locked together...building up stress-plates break free and slip all at once....causing earthquakeeg. San Andreas Fault in California fig 2.14

The Dynamic Mantle 7mantle- semi-liquid region between the crust and coreswirling motion of mantle cause lithospheric plates to move~ 45 hot spots on earth- place where magma (molten rock deep in mantle) wells upin mantle and forces its way up through lithosphere...cause volcanic activityGeysers- are volcanic activity produced by hot spots.hot spot below sea cause seamounts- underwater volcanoesif grow high enough create islandseg. Hawaiian Islandshot spot associated with mid-oceanic ridges- create 1 island or small clumpof islands, not a chain bcs they are not moving away from ridgeeg. Iceland, Galapagos Islands, AzoresGeological History of the EarthContinental Drift & Changing Oceans fig. 2.15The continents were once united in a single supercontinent called Pangaea thatbegan to break up about 180 million years ago. The continents have since moved totheir present positions.The Record in Sedimentssediment increases in thickness as move away from mid-oceanic ridgesTwo most abundant types of marine sediment are1. lithogenous sediment-comes from the weathering of rocks on land2. biogenous sediment -composed of the shells of marine organisms(diatoms, radiolarians, & foraminiferans).Biogenous sediment is made mostly of 1. calcium carbonate (CaCO3 )2. silica (Si O2 ).

Geological History of the Earth 8The Record in Sedimentsmicrofossil- microscopic shells and other remains of marine organisms that make upbiogenous sedimentsused to determine earth’s climate in pastcarbon dating- procedure used to determine the age of recent fossilsfind ratio of different atomic forms (isotope of carbon) to determine ageisotope -diff # of neutrons but same # protonsClimate and Changes in Sea LevelSea level falls during ice ages because water is trapped in glaciers on the continents. thelast major ice age occurred about 18,000 years ago.greenhouse effect- the increase in the earth’s temp bcs of CO2 in atmosphereCO2 in atm.imp:

The Geological Provinces of the Ocean 9Continental MarginsContinental Margins-edge of a continent; the zone between a continent and thedeep-sea floor fig 2.17*boundary b/w continental crust and oceanic crust3 parts: continental shelf, continental slope, continental rise1. continental shelf- shallow, gently sloping section that extends from the shore to thepoint where the slope gets steepermakes up 8% of ocean’s surface area yet is biologically richest part of oceanwhen sea-level low, shelf exposed to rivers and glaciers eroding deep canyonssubmarine canyon- a narrow, deep depression in continental shelfshelf break-section of continental shelf were the slope abruptly becomessteepershelf break is the end of continental shelf2. continental slope-steeper seaward section of the continental marginslope is closest thing to the exact edge of the continent3. continental rise- gently sloping area at the base of the continental slopeconsists of thick layer of sediment piled up on the sea floorContinental margins have three main parts. The continental shelf is the submerged part of thecontinent and is almost flat. The relatively steep continental slope is the actual edge of thecontinent. The continental rise is formed by sediments building up on the sea floor at the base ofthe continental slope.Active and Passive Marginsactive margin- a continental margin that is colliding with another plate and as a resultis geologically active fig. 2.20colliding plate slides below continental margin....form trenches...geologic activityeg. west coast of N. and S. Americapassive margin-a continental margin that is located at the “trailing edge” of a continent andas a result shows little geological activity fig. 2.20not a boundary between plates and is inactive geologically

Active and Passive Margins 10ACTIVE MARGINPASSIVE MARGINsteep rocky shorelinesnarrow continental shelfsteep continental slopeswide continental shelfgradual continental slopelack continental rise (sediment is down inthick continental rise(no tectonictrench or scraped up onto continent) process to remove sediment)West coast S. America & N. AmericaEast coast of N. & S. AmericaDeep-Ocean Basinsabyssal plain- nearly flat region of the deep-sea floordotted with seamounts-submarine volcanoesdeep trenches- oceanic plate colliding with oceanic plate (one sinks into mantle)Mid-Ocean Ridge and Hydrothermal Vents Fig. 2.23, 2.24, 2.25central rift valley- depression in mid-ocean ridgehydrothermal vents or deep-sea hot springs-place where heated seawaterforces its way up through the crust fig. 2.24, 2.25black smokers- chimney-like accumulation of mineral deposits that is found athydrothermal vents