Exploring the inner and outer shells of earth

WHY DO WE CARE ABOUT THE GEOMORPHOLOGY OF THE OCEAN FLOOR?

(in the context of Oceanography)

Earth's magnetic fieldI care!

Einstein described geomagnetism as one of the chief unsolved puzzles of physics. Neither Earth's liquid outer core nor its solid, yet superhot, inner core has struck scientists as likely sources of its magnetic field. Heat cooks the magnetism out of magnets, and liquefaction melts it away. Physicists were flummoxed.From Science News, Vol. 156, No. 20, November 13, 1999

Earth consists of a series of concentric layers or spheres which differ in chemistry and physical properties.

ChemicalLayers 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 innerstructure of the planet?

Seism

ic w

aves

Seismology is the study of elastic waves that travel through the earth

Two main wave types:

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)

Compression waves (P-waves): travel by squeezing and expanding medium they travel through. They can travel through both solids and liquids (e.g., sound waves).

• Seismic waves travel along there quickest route, generally through, the planetary interior to the seismic stations, changing speed every time material properties change.

Earthquake are an incredible source of seismic waves

Reconstructing the internal structure of the planet

• 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

solid

solid,more dense

Liquid Iron

solid Iron

• Combining information from many seismic waves we can get a detailed internal structure of the earth.

Seismic Velocity and Density

Other planets?

Earthquakes produce waves in the ocean

NOAA-GlobalOceanWave.mov

Courtesy: K. Satake, unpublished

Sea level: RISE FALL

Earthquakes produce waves in the ocean

World Seismicity (1900-2009)

Many large earthquakes occur along subduction zonesMost “Great” earthquakes are subduction mega-thrust events

Major Research Programs in Geophysics

http://www.earthscope.org/

http://www.margins.wustl.edu/

http://www.neptune.washington.edu/

http://earthquake.usgs.gov/earthquakes/

The Physiography of the North Atlantic Ocean Floor

http://topex.ucsd.edu

continental margins

deep oceanbasins midoceanic

ridges

• Continental margins

Continental Margin

• 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

• 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

• 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?

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.

2-3Geologic Differences between Continents and Ocean Basins

OCEANIC CRUST = THIN AND DENSER

CONTINENTAL CRUST = THICK AND LITHER

Geologic Differences between Continents and Ocean Basins

100 cm3 39 g

31.03 g/cm WATER

10 cm3 12 g

A

B

100 cm3 39 g

31.03 g/cm WATER

A

100 cm3 39 g

31.03 g/cm WATER

A=positively buoyant

B=negatively buoyant

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

NOAA-GlobalOceanWave.mov

NOAA-IndianOceanWave.mov

Exploring the inner and outer shells of earth