Download Chapter 7 Origin of Earth`s Atmosphere Earth`s atmosphere came

Chapter 7
Origin of Earth’s Atmosphere
Earth’s atmosphere came from gases vented by erupting volcanoes.
This process is known as outgassing.
Gases vented by erupting volcanoes contained mostly
water vapor(water in the form of gas), carbon dioxide and nitrogen.
Most of the hydrogen escaped into outer space due to its low density.
The carbon dioxide was used by living organisms that gave off oxygen.
The carbon dioxide was also absorbed by oceans.
As a result, nitrogen became the primary gas in our atmosphere.
Structure of the Atmosphere
Thermosphere
Mesosphere
Stratosphere
Troposphere (Contains most of the mass of the atmosphere)
(Lithosphere)
See ESRT p. 14
Changes in Air Temperature
At Earth’s surface in air temperature tend to be cyclic.
Our weather is controlled by:
Daily weather cycle
(*coldest temp. early morn. Late night; warmest mid-day)
Seasons
Temperature is measured by average vibrational energy of molecules.
The higher the temperature, the more kinetic (vibrational) energy the atmosphere contains.
Common thermometers have bulbs that contain liquids.
The liquids expand when the temperature increases.
The liquids contract as temperature decreases.
Three Scales for Measuring Temperature:
Fahrenheit & Celsius-measured in units of degrees
Kelvin-no degree sign
starts at absolute zero (considered to be the lowest temp.)
What Causes Air Pressure?
Air Pressure is also known as atmospheric pressure and is caused by the weight of the
Atmospheric pressure is measured in millibars (mb)
Air pressure is greatest at Earth’s surface and decreases with altitude.
At Earth’s surface air pressure is 1013.2 mb or 14.7 lbs. per inch.
This average sea level pressure of 1013.2 mb is equal to 1 atmosphere.
atmosphere.
Air pressure is exerted in all directions:
Example-When you drink from a straw you are actually lowering the air pressure inside
straw, increasing pressure on the liquid outside the straw. This increased pressure
pushes liquid up the straw.
the
Measuring air pressure:
Barometer-Instrument used to measure air pressure
These instruments used to use mercury, water other liquids in a tube.
Most modern barometers are called aneroid barometers and they use an airtight box to
rotate a pointer across a calibrated dial.
Factors that Affect Atmospheric Pressure:
AltitudeAtmospheric pressure decreases with altitude because as air rises, there is
less of the atmosphere above it pushing down. Because pressure is decreasing, air
expands as it rises, making it less dense.
TemperatureCooler air contracts and becomes more dense. It exerts more pressure on whatever is
beneath it causing atmospheric pressure to rise.
Heated air expands and becomes less dense, causing atmospheric pressure to
decrease.
Humidity(water vapor content of the air)Humid air is less dense than dry air.
As water vapor is absorbed into the atmosphere, the mass of the water molecules is less
dense than the nitrogen and oxygen molecules they displace. The air becomes less
dense which results in lower atmospheric pressure. As humidity increases, atmospheric
pressure decreases.
Dew Point: The temperature at which air
becomes saturated with moisture
(water vapor)
If temperature falls below the dew point, the air
can no longer hold as much water vapor, so the
water vapor condenses to liquid water.
Measuring moisture content of the atmosphere:
First, you would use a sling psychrometer.
Two thermometers mounted side by side.
One measures air temperature (dry bulb temp.)
The other has its bulb covered with a wet
cloth.
Evaporation of the water from the cloth causes this
thermometer to read a lower temperature.
(wet bulb temp.)
After you subtract the we bulb temperature from
the dry bulb temperature you can determine the dewpoint.
Use the table from the ESRT to determine the dew point.
Jet streams are currents, or very fast winds, that flow
in the upper atmosphere.
Jet streams do not follow the same patterns as
surface winds.
Jet streams usually blow from west to east in
mid-latitudes where cold polar air meets with
warmer tropical air.
Prevailing Winds:
Winds that blow more often from one direction
than from any other.
Winds and ocean currents tend to move the same way.
Coriolis Effect:
apparent curvature of the winds, ocean currents,
or objects moving along Earth's surface; caused by
Earth's rotation on its axis
How is wind measured?
Using an anemometer
wind speed
&
wind direction
Most precipitation starts as snow...why?
As snowflakes fall to lower elevations,
temperatures increase, and snow changes to rain...
What about the other forms of precipitation?
Drizzle: smaller raindrops that fall slowly
Sleet: partially frozen mixture of rain and snow
that occurs when the surface temperature
is just above freezing
Hail: "ice balls" associated with violent thunderstorms