Transcript 03-Core
Exploring the inner and outer shells of earth Earth consists of a series of concentric layers or spheres which differ in chemistry and physical properties. Chemical Layers Physical Layers Physical state is determined by the combined effects of pressure and temperature. • Increasing pressure raises the melting point of a material. • Increasing temperature provides additional energy to the atoms and molecules of matter allowing them to move farther apart, eventually causing the material to melt. • Both pressure and temperature increase toward the center of the Earth, but at variable rates. How do we learn about the inner structure of the planet? Seismology is the study of elastic waves that travel through the earth Two main wave types: Compression waves (Pwaves): travel by squeezing and expanding medium they travel through. They can travel through both solids and liquids (e.g., sound waves). Shear waves (S-waves): travel by shearing medium they pass through. S-waves can travel only through solids since particles need to be bonded to each other to propagate wave (similar to a bull whip) Earthquake are an incredible source of seismic waves • Seismic waves travel along there quickest route, generally through, the planetary interior to the seismic stations, changing speed every time material properties change. Reconstructing the internal structure of the planet • Combining information from many seismic waves we can get a detailed internal structure of the earth. • Crust & upper mantle: large increases in seismic velocities and density • Mantle: Gradual velocity and density increase • Outer core: dramatic density increase and no S-waves • Inner core: Jump in density and P-wave velocity, S-waves return Other planets? Seismic Velocity and Density solid solid, more dense Liquid Iron solid Iron Earthquakes produce waves in the ocean NOAA-GlobalOceanWave.mov NOAA-IndianOceanWave.mov Earthquakes produce waves in the ocean Sea level: RISE FALL Courtesy: K. Satake, unpublished World Seismicity (1898-2003) Mw ≥ 6.0 Mw ≥ 7.7 Many large earthquakes along subduction zonesevents Most “Great” earthquakesoccur are subduction mega-thrust Major Research Programs in Geophysics http://www.earthscope.org/ http://www.margins.wustl.edu/ http://www.neptune.washington.edu/ The Physiography of the North Atlantic Ocean Floor http://topex.ucsd.edu continental margins deep ocean basins midoceanic ridges • Continental margins are the submerged edges of the continents and consist of massive wedges of sediment eroded from the land and deposited along the continental edge. The continental margin can be divided into three parts: the Continental shelf, the Continental slope, and the Continental rise. Continental Margin • Deep Ocean Province is between the continental margins and the midoceanic ridge and includes a variety of features from mountainous to flat plains: Abyssal plains, Abyssal hills, Seamounts, and Deep sea trenches. Deep Ocean Basin • Midoceanic Ridge Province consists of a continuous submarine mountain range that covers about one third of the ocean floor and extends for about 60,000 km around the Earth. Midocean Ridge WHY DO LAND AND OCEAN EXIST? Geologic Differences between 2-3 Continents and Ocean Basins Continents and ocean basins differ in composition, elevation and physiographic features. • Elevation of Earth’s surface displays a bimodal distribution with about 29% above sea level and much of the remainder at a depth of 4 to 5 kilometers below sea level. • Continental crust is mainly composed of granite, a light colored, lower density (2.7 gm/cm3) igneous rock rich in aluminum, silicon and oxygen. • Oceanic crust is composed of basalt, a dark colored, higher density (2.9 gm/cm3) volcanic rock rich in silicon, oxygen and magnesium. Geologic Differences between Continents and Ocean Basins WHY DO LAND AND OCEAN EXIST? OCEANIC CRUST = THIN AND DENSER CONTINENTAL CRUST = THICK AND LITHER A B 100 cm3 39 g WATER 1.03 g/cm 10 cm3 12 g 3 A 100 cm3 39 g WATER 1.03 g/cm 3 A=positively buoyant B=negatively buoyant 100 cm3 39 g WATER 1.03 g/cm 3 A B 100 m3 39 kg WATER 1.03 g/cm 10 m3 12 kg 3 Isostasy refers to the balance of an object “floating” upon a fluid medium. Height of the mass above and below the surface of the medium is controlled by the thickness of the mass and its density (similar to ice floating in water). • Continents are thick (30 to 40 km), have low density and rise high above the supporting mantle rocks. • Sea floor is thin (4 to 10 km), has greater density and does not rise as high above the mantle. Oceanic Crust Versus Continental Crust Three spheres surround the rocky portion of the Earth. • Hydrosphere includes all of the “free” water of the Earth contained in the ocean, lakes, rivers, snow, ice, water vapor and groundwater. • Atmosphere is the gaseous envelope that surrounds the Earth and is mainly a mixture of nitrogen and oxygen. • Biosphere refers to all living and non-living organic matter. End of lecture Exploring the inner and outer shells of earth NOAA-GlobalOceanWave.mov NOAA-IndianOceanWave.mov Exploring the inner outer shells of earth WHY DO WE CARE ABOUT THE GEOMORPHOLOGY OF THE OCEAN FLOOR? (in the context of Oceanography)