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Transcript
Marine Science Unit 3 Earth Structure iceagenow.com 1st Day Objectives • Identify the layers of the Earth in the order in which they occur. • Know general characteristics of each layer (thickness, temperature, elemental composition) • What is isostatic equilibrium? • What is bouyancy? Layers of the Earth • • • • Inner Core Outer Core Mantle Crust myschoolhouse.com The Core • Made up of iron (90%) and nickel with some silicon, sulfur, and other heavy elements • Temperature of 5,500oC (9032oF) • The total core (inner and outer together) have an estimated radius of 3470km(5700mi) • 31.5% of the Earth’s mass and 16% of the Earth’s volume Inner Core • Theorized to be solid due to intense pressure • New evidence suggests that the inner core may get as hot as 6,600oC at its center – hotter than the surface of the sun news.sciencemag.org Outer Core • Less pressure than inner core it is theorized to be a dense liquid • Can have thermal plumes colorado.edu Mantle • Contains silicon and oxygen with some iron and magnesium • Estimated to be about 2,900km thick • Made up of the upper and lower mantle • 68% of the Earth’s mass and 83% of the Earth’s volume • Temperature-40006700oC volcano.oregonstate.edu Mantle • Upper Mantle • Lower Mantle – Made up of two layers – 1. Asthenosphere (asthenes=weak): The layer that is partially melted slowly flowing below the lithosphere extending to a depth of 350-650km – 2. Lithosphere (lithos=rock): Earth’s cool rigid outer layer that is 100-200km thick – Extends to the core – More dense and flows more slowly – Temperature 40006700oC • Made up of the rigid solid upper portion of the mantel and the crust ksl.com Crust • Thin solid outermost layer of the Earth • Relatively cool temperature • 0.4% of Earth’s mass and 1% of Earth’s volume • Composed of oxygen, silicon, magnesium, and iron • Oceanic Crust – Thin and made up of mostly basalt (heavy dark colored rock) • Continental Crust – Thicker and made up of mostly granite (light-colored rock) How does the crust float on the mantle? • Isostatic Equilibrium: Balance between the weight of the crust and the buoyancy provided by the mantle – As material adds to the oceanic crust or leaves the continental crust the balance becomes disrupted – Isostatic Rebound: The additional weight causes the crust to move down while the removal of material will cause the crust to move upwards – To restore equilibrium landmasses rise or sink along a weak area called a fault – One theory of what causes earthquakes is when landmasses on either side of an involved fault do not move together cliffsnotes.com Buoyancy • Archimedes’ Principle of Buoyancy: An object immersed in a fluid (gas or liquid) is buoyed up by a force equal to the weight of the fluid displaced – an object that weighs less than the fluid it displaces will float – If the weight of the crust changes, the landmass must rise or sink to compensate Journey to the Center of the Earth Activity • http://www.youtube.com/watch?v=bKVzVhqP Rf4 2nd Day Objectives • Explain the theory of Continental Drift. • Who developed the theory of Continental Drift? • Explain the different types of evidence that support the theory of Continental Drift. Theory of Continental Drift • 1912 Alfred Wegener proposes that the continents were once a single landmass that drifted apart (and are still doing so) • Pangaea (pan=all; gaea=ocean) “super continent” • Pathalassa (thalassa=the sea) single large ocean geo.tcu.edu Tectonic Jigsaw Activities 1 & 2 Compare the Pangaea you made in Activity 2 to the “real” Pangaea Continental Drift Evidence for Continental Arguments against drift: continental drift: • Shape of Continents • Distribution of minerals and fossil fuels • Distribution of plant and animal fossils • Wegener couldn’t explain how the continents drifted – Plate tectonics now provide an explanation for this • Jigsaw puzzle had gaps – Including the continental shelf fills in the gaps *Wegener disappeared on an expedition to Greenland before his theory became widely accepted… Evidence for Continental Drift • 1600’s - People notice the shape of continents fit together like a jigsaw puzzle • Mountain Range Distribution • http://dynamicearthass essmenttask.blogspot.c om/ rhnet.org Evidence for Continental Drift • Distribution of coal • Salt deposits – Coal forms from remains of plants and animals in swampy climates… coal is present in Antartica where there are currently no swamps – Salt deposits hundreds of millions of years old are found in locations where salt deposits don’t form • Limestone formation – Limestone forms from the remains of coral reefs – Limestone has been found in the north-central United states (where there is no sea water and is too far north to support coral reef growth) http://dynamicearthassessmenttask.blogspot.com/ Evidence for Continental Drift • Distribution of animal fossils – Ex. Lystrosaurus : bearlike extinct animal – Ex. Mesosaurus: Extinct aquatic reptile – Led scientists to conclude that 200 mill yrs ago Pangaea split into to continents • Lower - Gondwanaland • Upper-Laurasia en.wikipedia.org Evidence for Continental Drift • Distribution of plant fossils – 1855 Edward Suess found fossils of Glossopteris fern in South America, Africa, Australia, India, and Antartica – The seeds of this plant are too fragile to travel by sea and are too heavy to travel by wind… so, how did they get to so many different places? suu.edu Invention of Sonar • Detects objects under water by transmitting a sound and receiving an echo • SONAR is an acronym that stands for SOund Navigation and Ranging • Invented around the same time that Wegener proposed the theory of continental drift and partly in response to the wreck of the Titanic • Scientists almost immediately began using sonar technology to map the ocean floor – German Meteor expedition mapped the contours and depths of the South Atlantic in 1925 oscilatii2011.wikispaces.com 3rd Day Objectives • What are mid-ocean ridges, rift valleys, and trenches? • What is the theory of seafloor spreading? • What are three forms of evidence that support the theory of seafloor spreading? The Theory of Seafloor Spreading • In the 1960’s geologists Harry Hess and Robert Dietz hypothesize that the seafloor is in a constant state of creation and destruction • New crust emerges as magma from the asthenosphere pushes up through the rift and solidifies into new crust. This new crust pushes the old crust away from the ridge. • As this theory became accepted, other scientists hypothesized that old sea floor subsides or sinks at trenches as it is drawn downward by gravity and inertia (eventually it reaches the athenosphere and melts into magma again) • Is estimated to occur at about the same rate at which your fingernails grow. • http://www.suu.edu/faculty/c olberg/hazards/platetectonics /30_SeaFloor.html mail.colonial.net 3 Forms of Evidence of Seafloor Spreading 1. Ocean Bottom Sediment Samples – Cores samples from drilling showed that sediment layers were thin or absent at ridges and thicker away from the ridges – they found the thickest layers near continents 2. Radiometric Dating – Used to determine the age of rocks – Using this method, scientists have found seafloor rock to be much younger than continental rock and younger rocks near ridges and older rocks farther away. Drilling Core Samples of Ocean Sediments oceanexplorer.noaa.gov news.rutgers.edu Radiometric Dating of Seafloor ic.ucsc.edu 3 Forms of Evidence of Seafloor Spreading • 3. Magnetometer – Magnetometer: instrument that measures the polar orientation and magnetism of minerals – Symmetrical patterns in basalt (sea rock) show that seafloor on either side of the mid-ocean ridges mirror each other’s polar orientation tulane.edu Seafloor Spreading Activity 4th Day Objectives • What is the Theory of Plate Tectonics? • Explain the difference between convergent, divergent, and transform boundaries. • What is the Hot Spot Theory and how does it support the theory of Plate tectonics? • Explain plate movement. Theory of Plate Tectonics • Unifies Seafloor spreading and continental drift theories • Theory of Plate Tectonics: • The Earth’s lithosphere consists of more than a dozen separate plates – Plates are rigid and float on the lithosphere – Some plates are entirely ocean crust, some are entirely continental crust, and other plates are a combination – Plates move a few centimeters a year because of the movement of magma beneath them vulcan.wr.usgs.gov Plate Boundaries • Plate Boundaries = Where Plates Meet • 3 possible motions when plates meet: – Spreading Apart (Divergent Boundary) – Pushing Together ( Convergent Boundary) – Passing Side-by-Side (Transform Boundary) canarygeog.canaryzoo.com Divergent Boundaries • Two plates are moving apart • The crust pulls apart and forms • http://geology.com/nst valleys a/divergent-boundary• Mid-Ocean Ridges and rift oceanic.gif valleys mark divergent boundaries • Magma from the athenosphere flows up through the rift valley creating new crust and widening the seafloor • Volcanic activity at divergent boundaries can build mountains higher than sea level forming cotf.edu new islands – So, they are also known as constructive boundaries Convergent Boundaries • 3 Types: • Two plates are pushed – Oceanic plate colliding with together/colliding oceanic plate • AKA destructive boundaries • One plate sinks beneath the other • Can cause chain of volcanic islands to form – Oceanic plate colliding with continental plate • Oceanic plate is subducted underneath the continental plate and a trench forms • Can cause volcanic mountain range to form or earthquakes cotf.edu – Continental plate colliding with continental plate • Mountains form as the crust folds Transform Boundary • Two plates slide past each other • Earthquakes are common as rocks move when the plates slide Ex. San Andreas fault in California is the boundary between the Pacific Plate moving north and the N. American Plate moving south gweaver.net cotf.edu Comparing the 3 Types of Plate Boundaries Hot Spot Theory • 1963 – J. Tuzo Wilson observed that some volcanoes exist far from plate boundaries – He theorized that hot spots are small melting areas within the mantel where thermal plumes cause magma columns to push up through the crust (forming volcanoes) •Hot spots can occur at fault lines although most form far from plate boundaries Ex. Yellowstone •Hot spots do not move with tectonic plates, so volcanic areas change on the plate as it moves -This can result in a line or chain of volcanic islands pubs.usgs.gov windows2universe.org Plate Movement • Primary force driving plate movement = convection – Convection: Vertical circulation pattern in a gas or liquid caused by hot materials rising and cold materials sinking • This occurs in the mantel of the Earth when warm molten rock rises and cool magma sinks and creates a current that moves plates • Secondary driving force comes from seafloor spreading – As new seafloor forms, the plates tend to slide away from the elevated midocean ridges – The leading oldest oceanic plate tends to be dense and thick and may subduct/sink down Mountain Maker Earth Shaker… • http://www.pbs.org/wg bh/aso/tryit/tectonics/# 5th DaySediments in the Sea Objectives: • What techniques do scientists use to study ocean sediments? • How do scientists use ocean sediments to study the past? • How are sediments classified by size? • How are sediments classified by origin? • Explain the erosion and deposition of ocean sediments. • How does the rate of continental shelf sedimentation compare to the rate of ocean sedimentation? • http://www.inspirationg reen.com/magnifiedgrains-of-sand.html Marine Sediment • Sediment: Organic and inorganic particles accumulated together in a loose, consolidated form • Origins of sediment: – – – – – – Weathering Erosion Hard-shelled organisms Chemical processes Volcanic Activity Outerspace soest.hawaii.edu Why should we study marine sediments? • They are important to many Earth cycles: – Carbon – Nitrogen – Phosphorous • They play a principle role in plate tectonics as the “crust” • Scientists use them to understand the Earth’s past: – Climate – Ocean circulation patterns – Biological development • Deep within ocean sediments we find natural resources like: – Coal – Oil – Natural gas terradaily.com USGS Sediments PodCast • http://www.youtube.co m/watch?v=X2F2XNns5 X4 Studying Sedimentation • Stratigraphy: the study of sediment layers – Scientists look for clues like rock composition, microfossils, deposition patterns, and use them to draw conclusions about the past. scientificamerican.com Studying Sedimentation • Paleoceanography: Study of prehistoric oceans nps.gov – Study chemical ratios and radioactive isotopes found in microfossils to obtain evidence about prehistoric ocean conditions preachrr.wordpress.com Types of Sediments • Two most common ways to study sediments in by their: – Origin (where they came from) – Size • 4 Origin Categories: – – – – Lithogenous Biogenous Hydrogenous Cosmogenous • Size is classified by “grain” size (or the diameter of individual particles) – Wentworth Scale Classifying Sediments by Size WENTWORTH SCALE Classification Grain Diameter Example Clay Smaller than 0.004 mm Talc or fine powder Silt 0.004 mm - .0625 mm Powder Sand 0.0625 mm – 2 mm Sugar crystals Granule 2 mm – 4 mm Aquarium gravel Pebble 4 mm – 64 mm Grape Cobbler 64 mm – 256 mm Cobblestone Boulder 256 mm and larger Brick or larger Classifying Sediments by Size • Currents and waves tend to distribute sediments by size – The smaller a particle the more easily it is moved by the motion of the water – Heavier particles require more energy to move and therefore don’t travel as far as fine particles • Generally larger, heavier particles settle first… lighter, smaller particles take longer to settle • Erosion: Process by which sediments are removed/transported – Often by weathering, wind, human interaction • Deposition: Process by which sediments, soil, and rocks are added to a landform or land mass Lithogenous Sediments • Come from the land • • • • • Greek lithos=stone Greek generare=produce AKA terrigenous sediments Most abundant sediment by volume Results primarily from erosion by wind, water, and ice carrying rock and minerals into the sea or from landslides or volcanic eruptions • Majority of lithogenous sediments are near continents and islands • Quartz (from granite) is the most common mineral in lithogenous sediments because it is hard and doesn’t break down • Feldspar (also from granite) breaks down to form clay which is another common lithogenous sediment – although clay is often found farther from shore • Rivers carry up to 15 bill metric tons of lithogenous sediments into the ocean annually • 100 million metric tons of lithogenous sediments transfer from land to sea as fine dust and volcanic ash newark.osu.edu Hydrogenous Sediments • Nodules: Hydrogenous • From chemical thought to be reactions in seawater sediments produced by the some of • Greek hydro=water • Chemical reactions cause minerals to come out of solution and form particulates that settle on the bottom of the ocean • Accounts for less than 1% of all sea floor sediments • Found among biogenous and/or lithogenous sediments the slowest chemical reactions in nature… many nodules are more than 10 mill years old – Ferromanganese Nodules: Consist of iron, magnesium, and small amounts of cobalt, copper, chromium, molybdenum, and zinc – Phosphorite Nodules: Consist of phosphorite and other trace minerals Ocean Nodule www.oceanflore • The first nodules were discovered by the HMS Challenger Expedition in the 1870’s. • They are usually found in the abyssal plains of ocean floors. • http://www.isa.org.jm/f iles/documents/EN/Bro chures/ENG7.pdf Cosmogenous Sediments • From outerspace • Greek kosmos=space • Primarily made up of cosmic dust – Cosmic Dust: Small particles the size of sand or smaller – Thought to result from collisions between objects in space like asteroids and comets • Least abundant sediment and make up no more than a few parts per million of marine sediment • 15,000 to 30,000 metric tons of material from space reaches the Earth’s surface per year – Microtektites: glass particles that form when a large meteorite impacts Earth Biogenous Sediment • Come from organisms • Biogenous sediments cover the largest area of the sea floor • Greek bios=life • Most common in the deep • Particles in this sediment come ocean from shell and hard skeletons • Ooze: Deep ocean sediment – Plankton obtain siliceous and that consists of 30% or more calcareous from the sea water for biogenous sediment form shells/skeletons which later settle as sediment when the organisms die – Large organisms shells and hard corals also contribute to this sediment • Under the right conditions … they can form crude oil and natural gas – Accumulates slowly 1 to 6 cm per thousand years – Calcareous Oozes : Composed of plankton remains with calcium carbonate shells – Siliceous Ooze: Composed of plankton remains with silica skeletons http://upload.wikimedia.org/wikipedia/comm ons/thumb/3/31/Diatoms_through_the_micro scope.jpg/800pxDiatoms_through_the_microscope.jpg Continental Shelf Sediments • Continental Shelf: Located in relatively shallow water and near land • Mixture of both lithogenous and biogenous sediments • Tides, waves, and currents control continental shelf sedimentation – Surf and waves carry small particles out to sea which keeps most beaches sandy rather than muddy – Because waves and tides have less effect in deep water, mud is present off shore • Sedimentation rates on the continental shelf vary by region • Sedimentation is more rapid on the continental shelf than in the deep ocean • Continental sediments can affect the deep ocean with “avalanches” called turbidity currents – Thick muddy fluid rushes down from the continental shelf into the deep ocean forming turbidites Deep Ocean Sediments • High in biogenous material (from planktonic organisms) • Clay and other lithogenous material cover about 38% of the deep ocean floor – Their small size allows currents to carry them farther – Forms fine brown, olive, and red clay • Made up of 30% biogenous sediment known as ooze – Accumulates slowly 1 to 6 cm per thousand years • The Atlantic Ocean has twice the sediment that the Pacific Ocean has Carbonate Compensation Depth • The planktonic organisms that leave behind calcarous tests (skeletons) die everywhere in the ocean yet calcareous ooze is only fond in the deep ocean… why? • Calcium carbonate depth varies by region due to temperature and water chemistry • Seawater contains carbon dioxide and is more acidic below 3,000 meters which makes calcium carbonate more soluble in seawater – It also more soluble in the lower temperature of the deep water – At a certain point, calcium carbonate dissolves as fast as it forms= carbonate compensation depth Sediments as Economic Resources • 1/3 of the world’s crude petroleum and ¼ of the world’s natural gas come from sedimentary deposits on the continental shelf • Many geological oceanographers work in the petroleum and gas industry • Other important sediment resources include: – Evaporates like salt, gypsum, calcium carbonate (which are hydrogenous sediments) – Metal sulfide – Dissolved minerals – Sand and gravel (for construction – Diatomaceous earth – water filters, toothpaste, car polish, paints, etc. Sediments Song… • http://www.youtube.co m/watch?v=rvh_DnwrD dM