Transcript oceans
MARINE GEOLOGY http://www.scribd.com/doc/135191/Volcanic-Island-Formation-in-the-South-Pacific Geology • Study of the development and physical characteristics of our planet’s seafloor and continents and the forces that shape them • How did the oceans and continents form? www.grandunificationtheory.com/summary.htm Big Bang • 20 billion years ago • Matter (all elements in periodic table) expanded into space • Matter clumped and planets formed 5 bya • Early on our planet is a hard rock being bombarded by other planetary bodies and experiencing volcanic eruptions http://geology.about.com/od/meteorites/ig/meteorites/chondrite2.htm 82 percent of meteorite falls are chondrites Formation of Earth’s Layers 1. Heating (leftover radioactive heating) Denser (Fe and Ni) material sunk to the center Lighter (Si and O) material rose to surface Some materials vaporized to form early oceans and atmosphere 2. Layers formed 3. Planet cools Our “usual” image of Earth http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html Evidence for layers from Seismic Waves http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html http://www.windows.ucar.edu/tour/link=/earth/images/earthint_image.html&edu=mid Early Atmosphere • 3.5 bya • Water vapor, carbon monoxide, hydrogen sulfide, nitrogen and cyanide www.lpi.usra.edu Early Oceans amp.wpcamr.org/archives/date/2007/12 • 4 bya water vapor from mantle is cooled and collects on surface. • 1000’s of years of thunderstorms and rain • Low lying spots fill to become our early oceans • Water also from comets, volcanoes, meteors, geysers, rocks that contain moisture Origin of the Continents • Alfred Wegener suggested the continents were not always on their present positions • Continental Drift • 200mya a single landmass called Pangea broke up • Evidence – Coastlines fit like a puzzle – Similar fossils and rock formations on different continents Problems With CD • No mechanism for how the continents “drift” • Wegener was a meteorologist…what did he know anyway!!! www.geography-site.co.uk CRUST – thin outer layer • less dense, rocks that floated to the surface when the Earth was formed • between 35km and 70km thick. – not a continuous layer of rock • Split into plates, which are free to drift slowly across the surface of the planet. Moving Plates • Continents move 1 cm/yr • Boundary between plates is a fault – Seismic activity occurs at faults • The lower mantle is heated by the core which creates convection currents • Rising magma may break thru the crust at ridges like the Mid-Atlantic Ridge Moving Plates • Sea floor spreading- plates move apart from rising magma at a ridge • Subduction- two plates collide and the denser plate sinks into the mantle – Forms trenches (Marianas Trench) – Trenches are the deepest parts of the ocean Ocean Floor Formation • Sea floor spreading is source of new ocean floor • Subduction recycles ocean floor back into the mantle • Atlantic is growing • Pacific is shrinking Sea Floor Spreading Evidence • Younger rocks are found closer to the ridge • Less sediment closer to the ridge • Polarity of magnetic minerals is mirror image on either side of the ridge – N and S pole flip periodically – Minerals line up as magma cools with the N pole Plate Tectonics • Unifying theory that combines continental drift and sea floor spreading • Explains the origin of, connections between earthquakes, volcanoes, faults, continental drift and sea floor spreading • Explains how oceans and its features are formed Why We Have Oceans & Why The Ocean Floor Is Not Flat en.wikipedia.org Ocean Floor Topography • Average ocean depth is 3636 m • Sonar is used to map features of the ocean floor • The study of elevations and depressions is topography Oceanic crust is denser than continental crust sinks lower into the mantle This is why it is filled w/ water and has become an ocean basin. 2 Types of Crust •Continental crust •less dense (lighter) •floats on the mantle •35- 70 km thick •3500 million years old •Oceanic Crust •6 Km thick •Younger than 200 million years •Sinks into mantle Typical Features • Continental Shelf-extension of the continent • Continental Slope- steep drop off from shelf and end of the continent and it’s crust • Submarine Canyons- deep valleys in the slope created by underwater landslides or old rivers • Continental Rise- a pile of sediment that has slid down the slope • Seamounts and Guyots- Islands created by underwater volcanoes Plate Tectonics and Continental Coastlines • Active margins (California) –Sites of tectonic activity earthquakes, volcanoes, mountains, –Narrow c. shelf and steep slope ending in trench • Passive –Little to no tectonic activity –Wide shelf, pile of sediment at the bottom of the slope Plate Margins • Converging plates –O & C- oceanic subducts under continental: trenches, volcanic islands & earthquakes –O & O- one plate subducts under the other: trenches, volcanic islands & earthquakes –C & C- mountains& earthquakes Features of Ocean Ridges • Water is superheated (371 C) by hot magma and dissolves minerals from nearby rock • As water comes out from the rock it looks like smoke • Area with these hot springs is called a hydrothermal vent Animals From Hydrothermal Vents • Bacteria are the base of the food chain • Chemosynthesis- make sugars using energy from compounds like H2S • Other vent animals include giant tubeworms, crabs, octopus, shrimp and mussels WHY LEARN ABOUT GEOLOGY • Nature of our planet and its changes • Impact on human life • Predicting future natural disasters Distribution of our Oceans • Cover ¾ of our planet • Southern hemisphere is 80% ocean while Northern hemisphere is 60% ocean • Separate but connected basins • Include features like… • Most of the ocean bottom is an abyssal plain Ocean Bottom Review • • • • Shelf Slope Rise Ocean basin • Continental shelf • Narrow shelf • Wide shelf Continental Margins • ACTIVE MARGINS – Trench • PASSIVE MARGINS – Abyssal plain PLATE TECTONICS • Outer layer of our planet move and deform • Boundary • Converging • Diverging • Transform EVIDENCE • Continental drift • Sea floor spreading – Diverge – Ridges • Subduction – Converge – Trenches