Download interior structure of the earth

MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 5: EARTH’S ATMOSPHERE AND OCEANS
CLASS NOTES
EARTH’S FIRST ATMOSPHERE
The Earth had an atmosphere before the Sun was fully formed five billion years ago (5 BYA). This
primitive atmosphere was composed of hydrogen and helium.
EARTH’S SECOND ATMOSPHERE
The next step occurred when gases trapped in Earth’s hot interior escaped through volcanoes and
fissures. The atmosphere composition was: 85% water vapor, 10% carbon dioxide, and 5% nitrogen.
EARTH’S THIRD ATMOSPHERE
The production of free oxygen did not occur until the primitive plants known as stromalites and green
algae appeared. Stromalites and green algae, like all green plants, use photosynthesis to convert carbon
dioxide and water to hydrocarbon and oxygen:
CO2 + H2O + light  CH2O + O2.
EARTH’S MODERN ATMOSPHERE
With the production of free oxygen, an ozone layer (O3) formed in the upper atmosphere. The ozone
layer acts like a filter to reduce the amount of harmful ultraviolet radiation reaching the Earth’s
surface.
ATMOSPHERIC PRESSURE
Gravity holds gas molecules close to the Earth’s surface. The density of air molecules is greatest at the
Earth’s surface and decreases with height. Because air molecules have weight, they exert atmospheric
pressure on the ground.
ATMOSPHERIC GASES
Earth’s present-day atmosphere is a mixture of various gases: primarily nitrogen (78%) and oxygen
(21%). It also contains small percentages of water vapor, argon, and carbon dioxide.
STRUCTURE OF THE ATMOSPHERE
The Earth’s atmosphere is divided into layers based on temperature differences. From surface to outer
space, the layers of the atmosphere are: troposphere, stratosphere, mesosphere, thermosphere, and
exosphere.
TROPOSPHERE
Almost all weather occurs in the troposphere, the lowest layer of the atmosphere. The troposphere
extends to a height of 10 kilometers and contains 90% of the atmosphere. Air temperature steadily
decreases from the Earth’s surface to the bottom of the stratosphere, the next layer of the atmosphere.
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THE TROPOSPHERE AND STRATOSPHERE
STRATOSPHERE
Above the troposphere is the stratosphere, which reaches a height of 50 kilometers. Ultraviolet
radiation from the Sun is absorbed by the ozone layer near the top of the stratosphere. Temperature in
the stratosphere varies from – 50o C at the bottom to 0o C at the top.
MESOSPHERE
Above the stratosphere, lies the mesosphere. The mesosphere extends upward from 50 to 80
kilometers. The gases that make up the mesosphere absorb very little of the Sun’s radiation. As a result,
the temperature decreases from 0o C at the bottom of the mesosphere to - 90o C at the top.
THERMOSPHERE
Extending upward from 80 – 500 km above the Earth’s surface, the thermosphere contains very little
air, but absorbs enough solar radiation to reach 2000oC. The ionosphere is an ion-rich region within the
thermosphere. The charged particles within the ionosphere are produced from the interaction between
high-frequency solar radiation and atmospheric ions.
EXOSPHERE
The exosphere is the uppermost layer of Earth’s atmosphere. It extends above the thermosphere and
contains air molecules that can eject into outer space.
DISTRIBUTION OF SOLAR ENERGY
The temperature of Earth’s surface ultimately depends on the Sun. The Sun provides radiation measured
in terms of energy per unit of surface area. Energy per unit area depends on the angle between the Sun’s
rays and the Earth’s surface.
DISTRIBUTION OF LIGHT ENERGY
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THE SEASONS
The tilt of the Earth and the corresponding angle of solar radiation produce the yearly cycle of seasons.
EARTH’S SEASONS
SOLAR CONSTANT
The amount of solar energy received by the Earth is measured by the solar constant. Imagine a square
pane of glass measuring 1 meter on a side and floating at the top of the atmosphere. The amount of solar
energy that strikes this imaginary pane of glass (the solar constant) is 1400 joules per second (1400
W/m2).
THE SOLAR CONSTANT
TERRESTRIAL RADIATION
The Earth absorbs solar radiation. In turn, it re-radiates part of it back to outer space in the form of
infrared radiation. This is called the greenhouse effect, and it plays a significant role in global
warming.
THE GREENHOUSE EFFECT
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SALINITY
Salt makes up 99.7% of the ocean’s dissolved materials. The amount of dissolved salt in seawater is
called salinity. Salinity is the mass of salt dissolved in 1000 grams of seawater. Seawater is fairly
uniform around the world: 96.5% water and 3.5% salt.
LAYERS OF THE OCEAN
Scientists have categorized the ocean into three vertical layers: the surface zone, the transition zone,
and the deep zone.
THE OCEAN’S VERTICAL STRUCTURE
SURFACE ZONE
The top layer of the ocean, the surface zone, represents two percent of the ocean’s volume. Seawater in
the surface zone is well-mixed and adjusts vertically in response to changes in Earth’s atmosphere.
TRANSITION ZONE
Below the surface zone is the transition zone. The transition zone is the area between the surface and
the deep ocean. Sea water within the transition zone moves horizontally according to density changes.
DEEP ZONE
Below the transition zone is the deep zone, a fairly uniform area that accounts for 80% of the ocean’s
volume. The deep zone is nearly isolated from contact with the atmosphere.
CONVECTION CURRENTS
As warm air rises, it expands and cools. Cooler air aloft sinks to occupy the region left vacant by rising
warm air. This circulation of air is called a convection current.
WIND
Wind results when convection currents stir the atmosphere. Wind is the movement of air along the
Earth’s surface. Winds are generated in response to pressure differences in Earth’s atmosphere, which
are largely the result of temperature differences.
PRESSURE-GRADIENT FORCES
A difference in air pressure between two different locations is called a pressure-gradient. When air
moves against an object, it exerts a force on that object. This is the pressure-gradient force.
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AIR CIRCULATION
The underlying cause of air circulation is unequal heating of the Earth’s surface. On a global scale,
equatorial regions receive the most energy from the Sun. As air heated at the equator rises, it moves in
the upper atmosphere towards the polar regions and sinks at the poles. Then it moves back to the
equator along the ground.
THE CORIOLIS EFFECT
The Earth’s day-night rotation greatly affects the path of moving air. Think of the Earth as a large
merry-go-round. You and a friend are playing catch. Although the ball travels in a straight-line path, it
appears to curve to the right.
EXAMPLE OF CORIOLIS EFFECT
EFFECTS OF CORIOLIS EFFECT
The result of the Coriolis effect is the deflection of winds toward the right in the Northern Hemisphere
and to the left in the Southern Hemisphere.
NORTHERN HEMISPHERE
SOUTHERN HEMISPHERE
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GLOBAL CIRCULATION PATTERNS
Global winds are the result of unequal solar heating of the Earth’s surface coupled with the effects of the
Earth’s rotation.
GLOBAL WINDS
UPPER ATMOSPHERIC CIRCULATION
“Rivers” of rapidly moving air meander around the Earth 10 kilometers off the ground. These highspeed winds are called the jet streams. With wind speeds averaging 100 miles per hour, the jet streams
play an essential role in the global transfer of solar energy from the equator to the poles.
OCEANIC CIRCULATION
The forces that drive the winds also drive ocean currents. In the open ocean, the major movement of
seawater results from two types of currents: wind-driven surface currents and density-driven deepwater currents.
SURFACE CURRENTS
As winds blow across the ocean, frictional forces set surface waters into motion. If distances are short,
the surface waters move in the same direction as the wind. For longer distances, the Coriolis effect
causes surface waters to spiral in a pattern called a gyre.
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CIRCULATION OF THE OCEAN’S SURFACE WATERS
DEEP-WATER CURRENTS
Surface waters are driven by winds, but deep waters are driven by gravity. Deep-ocean currents act
like a conveyor belt, transporting cold water from the North Atlantic to the equator, and then to the
Antarctic. From the Antarctic, water flows eastward then northward into the Pacific and Indian Oceans.
DEEP-OCEAN CURRENTS
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