Transcript PPT

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 field
I 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.
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
Earthquakes produce waves in the
ocean
Sea level:
RISE
FALL
Courtesy: K. Satake, unpublished
World Seismicity
(1900-2009)
Many large earthquakes occur along subduction zones
Most “Great” earthquakes are subduction mega-thrust events
Major Research Programs in Geophysics
http://www.earthscope.org/
http://www.margins.wustl.edu/
http://earthquake.usgs.gov/earthquakes/
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
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?
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
OCEANIC CRUST = THIN AND DENSER
CONTINENTAL CRUST = THICK AND LITHER
A
B
100 cm3
39 g
WATER
10 cm3
12 g
1.03g/cm
3
A
100 cm3
39 g
WATER
1.03g/cm
3
A=positively buoyant
B=negatively buoyant
100 cm3
39 g
WATER
1.03g/cm
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