Introduction to Oceanography

Layers of the Earth

Layers Crust Mantle Core Asthenosphere Mesosphere Outer Core Inner Core

Crust 2 types 1. Continental- 30-70 km thick 2. Oceanic- 8 km thick

Lithosphere Crust and Upper Mantle Made of 7 major plates Solid

Asthenosphere Semi solid (Plastic) Magma is formed here Magma Convection currents Lithosphere (plates) move on top of asthenosphere

Mesosphere Solid because of high temperature and pressure

Outer Core Nickel and Iron Liquid Spins around inner core Causes the Earth’s Magnetic Field Very dense

Inner Core Nickel and Iron Solid Extreme high temperatures and pressure- compacts molecules=solid

Plate Movement- Past, Present and Future

Plate Tectonics The Theory of Plate Tectonics Plate Boundaries Spreading Centers(Divergent) Subduction Zones(Convergent) Sliding Faults (Transform) Plate Movement

The Theory of Plate Tectonics “Continental Drift” - theory* proposed by Alfred Wagner, a German meteorologist (1915) Explained by: geologic fit fossils * Not accepted by scientific community - no mechanism to explain plate movement

Plate Tectonics - evidence for theory of continental drift The Theory of Plate Tectonics (cont’d.) Plate Tectonics - evidence for theory of continental drift Found 3 types lithospheres plate boundaries, ridges (spreading centers) Divergent trenches (subduction zones) Convergent transform faults (plates sliding past one another)

Constructive Margin Mid-Ocean Ridge Destructive Margin  Subduction Zones Constructive Margin Transform

Conservative Margins-Transform Faults

Driving Mechanisms for Plate Motions 3-3 Constructive margins Midocean ridges Destructive margins Subduction zones Driving Mechanisms for Plate Motions

Density differences – cool vs. hot Plate Boundaries a) Divergent- Spreading centers - ‘rift zones’ Process: Convection cells form Density differences – cool vs. hot Convection cells cause frictional drag on lithosphere Lithospheric crust weakens

Faulting – break in overlying lithosphere Magma flows upward Plate Boundaries (cont’d.) a) Spreading centers - ‘rift zones’ (cont’d.) Faulting – break in overlying lithosphere Magma flows upward New lithospheric crust formed

Plates split apart -‘divergent plate’ boundary Plate Boundaries (cont’d.) a) Spreading centers - ‘rift zones’ (cont’d.) Plates split apart -‘divergent plate’ boundary New crust formed - ‘constructive’ plate boundary Convection Video

Lithospheric Plates collide - ‘convergent’ plate boundary Plate Boundaries (cont’d.) b) Convergent- Subduction zones Lithospheric Plates collide - ‘convergent’ plate boundary Crust destroyed - ‘destructive’ plate boundary Forms trenches and mountains

3 types of subduction zones: Plate Boundaries (cont’d.) b) Subduction zones (cont’d.) 3 types of subduction zones: Ocean lithosphere into continental lithosphere – form trenches and mountain ranges Ex. a): Cascade Mtn. Range Ex. b): Andes Mtn. Range

Plate Boundaries (cont’d.) b) Subduction zones (cont’d.) Ocean lithosphere into ocean lithosphere – forms trenches and island arcs Ex. A): Aleutian Islands (Alaska) Ex. B) Isthmus of Panama

Plate Boundaries (cont’d.) b) Subduction zones (cont’d.) Continental lithosphere into continental lithosphere – form mountain ranges Ex. A) Himalayas

Plates slide past one another Plate Boundaries (cont’d.) c) Transform faults Plates slide past one another Lithospheric crust neither created nor destroyed - ‘conservative’ plate boundary Ex. A) San Andreas Fault

Plate Boundaries (cont’d.)

New crust is created at spreading centers at a rate of approximately Plate Movement New crust is created at spreading centers at a rate of approximately 1-10cm per year Old crust is destroyed at the same rate at subduction zones

Magnetic anomalies in ocean crust...look at spreading centers Plate Movement (cont’d.) Magnetic anomalies in ocean crust...look at spreading centers paleomagnetism every so often Earth’s magnetic field flips (every 300K-500K years) magnetic signal recorded in crust at spreading center as it’s formed

More evidence of plate moving..

Plate Boundaries (cont’d.)

islands or sea mountains formed over hotspots Plate Movement (cont’d.) Hot spots Hawaiian Islands islands or sea mountains formed over hotspots (fixed area where magma comes up) lithosphere moves over hotspot volcanic mountain over hotspot and in ‘front’ of hotspot

Hot Spots?

3-3 Mantle plumes deep in the asthenosphere as molten rock which rises and melts through the lithospheric plate forming a large volcanic mass at a “hot spot”.

Age of Ocean Crust http://www.ngdc.noaa.gov/mgg/geology/geology.html

Geological Periods

Geological Periods Precambrian 4.6 B - 570 Ma solidification Cambrian 514 Ma Gondwana, hard shell anim. Ordovician 458 Ma separation, coldest Silurian 425 Ma Laurentia collides with Baltica Devonian 390 Ma pre-Pangea, equatorial forests Early Carboniferous 356 Ma Late Carboniferous 306 Ma western Pangea is complete Permian 255 Ma deserts, reptiles, major ext. Triassic 237 Ma Life begins to rediversify,Pangea Jurassic 195 Ma Dinosaurs, Pangea starts to break Late Jurassic 152 Ma Pangea rifts apart, Atlantic Cretaceous 94 Ma New oceans, India K/T extinction 66 Ma end of dinosaurs Eocene 50.2 Ma India collides with Asia Miocene 14 Ma Modern look Modern Future World +50 Ma N. Atlantic widen Future +100 Ma new subduction Future +250 Ma new Pangea

Precambrian break-up of the supercontinent, Rodinia, which formed 1100 million years ago.   The Late Precambrian was  an "Ice House" World. Source: www.scotese.com Cambrian Animals with hard-shells appeared in great numbers for the first time during the Cambrian.  The continents were flooded by shallow seas.  The supercontinent of Gondwana had just formed and was located near the South Pole.

Ordovician The end of the Ordovician was one of the coldest times in Earth history.  Ice covered much of the southern region of Gondwana. Silurian Coral reefs expand and land plants begin to colonize the barren continents.

Devonian By the Devonian the early Paleozoic oceans were closing, forming a "pre-Pangea".  Freshwater fish were able to migrate from the southern hemisphere continents to North America and Europe.  Forests grew for the first time in the equatorial regions of Artic Canada. Early Carboniferous During the Early Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains.   An ice cap grew at the South Pole as four-legged vertebrates evolved in the coal swamps near the Equator.

Late Carboniferous By the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form  the western half of Pangea.  Ice covered much of the southern hemisphere and vast coal swamps formed along the equator. Permian Vast  deserts covered western Pangea during the Permian as reptiles spread across the face of the supercontinent.

Triassic The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole; and warm-water faunas spread across Tethys. The first mammals and dinosaurs appeared; Jurassic By the Early Jurassic, south-central Asia had assembled.  A wide Tethys ocean separated the northern continents from Gondwana.  Subduction zone Rocky Mountains

Formation of the Rocky Mountains http://wrgis.wr.usgs.gov/docs/parks/province/rockymtn.html

Late Jurassic In the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America.  Cretaceous Notice that North America was connected to Europe, and that Australia was still joined to Antarctica.

K/T extinction The bull's eye marks the location of impact site of a 10 mile wide comet caused global climate changes that killed the dinosaurs and many other forms of life.  By the Late Cretaceous the oceans had widened, and India approached the southern margin of Asia. Eocene 50 - 55 million  years ago India began to collide with Asia forming the Tibetan plateau and Himalayas (destroying the last of Tethys ocean).  Australia, which was attached to Antarctica, began to move rapidly northward.

Miocene 20 million years ago, Antarctica was covered by ice and the northern continents were cooling rapidly.  The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea. Arabia moved away from Africa forming Gulf of Aden and Red Sea; Last Ice Age When the Earth is in its "Ice House" climate mode, there is ice at the poles.  The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles).  The last expansion of the polar ice sheets took place about 18,000 years ago. 

Modern World If we continue present-day plate motions the Atlantic will widen, Africa will collide with Europe closing the Mediterranean, Australia will collide with S.E. Asia, and California will slide northward up the coast to Alaska.

Future +100 Earth is ~ 4.6 bill years old – suggested cyclic of 500 mill year pattern of assembling and disassembling the land masses; Future +250