Download The Planet Oceanus

The Planet Oceanus
2-1
The Earth’s Structure
Earth consists of a series of
concentric layers or spheres
which differ in chemistry and
physical properties.
The compositional layers of
the Earth are the Crust, the
Mantle, and the Core. The
Core is subdivided into a
molten outer core and solid
inner core.
Layered Earth - Chemical Properties
Layer
Continental Crust
Oceanic Crust
Mantle
Core
Chemical Properties of Earth’s Layers
Chemical Properties
Composed primarily of granite
density = 2.7 g/cm3
Composed primarily of basalt
density = 2.9 g/cm3
Composed of silicon, oxygen, iron and magnesium
density = 4.5 g/cm3
Composed mainly of iron
Density = 13 g/cm3
Note that Earth is density stratified, that is, each deeper
layer is denser than the layer above.
Layered Earth - Physical Properties
Layer
Lithosphere
Asthenosphere
Mantle
Outer Core
Inner Core
Physical Properties of Earth’s Layers
Physical Properties
The cool, rigid outer layer
Hot, partially melted layer which flows slowly
Denser and more slowly flowing than the
asthenosphere
Dense, viscous liquid layer, extremely hot
Solid, very dense and extremely hot
So, when we examine the chemical and physical properties of
Earth’s layers, we see that a cool, rigid, less dense layer (the
lithosphere) floats on a hot, slowly-flowing, more dense layer
(the asthenosphere).
Layered Earth - Evidence Of Earth’s Layers
What evidence supports the idea that Earth has layers?
The behavior of seismic waves generated by earthquakes give scientists
some of the best evidence about the structure of Earth.
(above-left) S waves cannot penetrate Earth’s liquid core.
(above-right) P waves are bent as they pass through the liquid outer core.
2-1 Structure
The Earth’s
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, causing
the material to melt.
• Both pressure and
temperature increase
toward the center of the
Earth, but at different rates.
• Divisions of the Earth based
upon physical state are the
Lithosphere, The
Asthenosphere, the
Mesosphere, the Outer core,
and the Inner core
2-1
The Earth’s
Structure
Three fluid 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.
The air on earth is held by
gravity, pressure, and density
accordingly decreases with
pressure. Log P = -0.06 (H),
where P is pressure and H is
altitude in km.
At 700 km above sea level one
encounters an almost perfect
vacuum.
By definition boundary of
atmosphere set at 1000 km
Exosphere-the sphere above
the atmosphere - is where
molecules escape into space
and have to pass through the
magnetosphere
2-2
The Physiography
of the
Ocean Floor
Physiography and bathymetry (submarine
landscape) allow the sea floor to be subdivided
into three distinct provinces: continental
margins, deep ocean basins and 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.
•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
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
2-3 between Continents and Ocean
Geologic Differences
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.
2-3
Geologic Differences
between Continents and
Ocean Basins
•The moho is the boundary between
rocks of the crust and the denser (3.3
gm/cm3) rocks of the mantle.
Geologic Differences between
Continents and Ocean Basins
2-3
Continents and ocean
basins differ in
composition, elevation
and physiographic
features.
2-3
Geologic Differences
between Continents and
Ocean Basins
Isostacy 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).
• Greater the density of the mass, the lower it will sink in the
medium.
• Greater the thickness of the mass, the higher a portion of it
will rise above the medium.
• 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.