Origin of the atmosphere

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Earth science the study of the Earth and its
processes Geology - study of nature and
development of Earth (how does it work and how
did it get that way) Geography - science of
distribution of Earth's features and human's
effect on them (what is it like right now and
how does it relate to people)
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Earth

• 3rd planet from the sun (93 million miles away)
• 71 Earths surface is covered by water
• The only planet with a climate that allows water
  to exist in 3 phases (ice, liquid, vapor)
• The only planet in our solar system to have an
  atmosphere that allows life to exist

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Solar System Formation and Structure  

• Gravity
• Mutual attracting force exerted by mass on all
  other objects
• Planetesimal hypothesis
• Suns condense from nebular clouds

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PLANETARY EVOLUTION
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PLANETARY EVOLUTION
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Origin of the atmosphere

• The original atmosphere
• Probably made up of hydrogen and helium.
• These are fairly common in the universe.
• Original atmosphere stripped away by the solar
  wind
• H and He are very light
• Hydrogen and helium have the smallest atoms by
  mass.
• The early earth was not protected by a magnetic
  field.
• Thus the current atmosphere is secondary

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• As Earth formed by accretion of matter
• once it reached 3/10 of its current diameter,
  Earth had enough gravity to begin holding gases
  in an atmosphere
• this secondary atmosphere was mainly water vapor
  and CO2 (both greenhouse gases)

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The secondary atmosphere

• Formed from degassing of volcanoes
• Gasses emitted probably similar to the gasses
  emitted by volcanoes today.
• H2O (water), 50-60
• CO2 (carbon dioxide), 24
• SO2 (sulfur dioxide), 13
• CO (carbon monoxide),
• S2 (sulfur),
• Cl2 (chlorine),
• N2 (nitrogen),
• H2 (hydrogen),
• NH3 (ammonia) and
• CH4 (methane)

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• CO2 is a colorless gas
• allows the sun's visible radiation to pass
  through to Earth's surface
• radiation is absorbed and re-emitted as infrared
  radiation
• some of infrared radiation is reabsorbed by CO2
  and some is bounced back to the surface
• this causes the temperature at the surface of
  Earth to increase to extremely high levels

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• H2O water vapor
• is an even stronger greenhouse gas
• temperatures at the surface would have been so
  high that water could only exist as a gas
• the planet would have been totally covered in
  clouds of vapor
• Over time the planet was fully formed at its
  current size and started cooling
• the water vapor condensed and it started to rain
• a lot
• this eventually formed the first ocean

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Occasionally asteroids would still hit the
planet some were large enough to vaporize the
whole ocean, sending steam into the atmosphere
until it condensed and rained out again (it is
thought that the moon was formed by a very large
planet-sized body crashing into Earth sometime
before 4.6 by ago causing a huge chunk of Earth
to escape gravity and begin orbiting Earth)
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Eros. Taken by NEAR http//nssdc.gsfc.nasa.gov/img
cat/hires/nea_0127504836_mos.jpg
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Modern atmosphere

• Nitrogen (N2)-
• 78,
• Oxygen (O2)-
• 21,
• Carbon Dioxide (CO2) 0.03 ,
• Where did all the oxygen come from?

The current atmosphere traps enough heat to keep
the planet from freezing
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• Where did all the O2 come from?
• Where did all the CO2 go?

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Formation of the oceans

• The earth is cool enough that H2O condenses to
  form the oceans.
• Estimates of the amount of H2O outgassed is not
  enough to fill the oceans
• It seems likely that a large volume of water was
  added by the impact of icy meteors on the
  atmosphere.
• CO2 dissolves into the oceans.

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In the oceans life evolves

• Ingredients necessary for life
• NH3 ammonia
• CH4 Methane
• H2O Water
• These can produce amino acids, the building
  blocks of life

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• Life may have originated
• under the primitive atmosphere
• or at hydrothermal vents deep in the oceans
• or deep in the earths crust

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Life changes the atmosphere

• With the evolution of life the first cellular
  organisms (cyanobacteria) began to use the gasses
  in the early atmosphere (NH3 ammonia, CH4
  methane, H2O water) for energy.

Photosynthetic organisms evolve. These
organisms use CO2 and produce oxygen (O2) as a
waste product.
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• Where did the O2 come from?
• Produced by photosynthetic life.
• Where did the CO2 go?
• Dissolves in water in the oceans
• Used by life by photosynthesis and buried when
  plants and micro-organisms die.
• The source of coal and oil

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Early history of life and the atmosphere

• The Earth is about 4.5 billion years old.
• Life first appears in the oceans at least 3.5
  billion years ago.
• 0.9 billion years ago there is enough oxygen in
  the atmosphere to produce the ozone layer and
  life can finally move onto land.
• The ozone layer protects the earth from harmful
  ultra violet radiation from the sun.

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Figure 2.1
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The other planets

• Venus
• Closer to the sun
• Very hot at the surface so water vapor in the
  atmosphere does not condense.
• Runaway greenhouse effect (482oC, 900oF).
• No oceans or rainfall so CO2 does not dissolve.
• Has a very dense atmosphere.

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From Venera 13
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The other planets

• Mars
• Further from the sun
• Smaller than Earth
• So small that most of the atmosphere escaped into
  space.
• No oceans or rainfall so CO2 stays in atmosphere.
• 98 of atmosphere is CO2.

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• Jupiter
• Huge (318x earths mass)
• Kept all its original atmosphere
• 80 Hydrogen
• 20 Helium

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• Scientific Method - the basis for all the
  sciences
• 1. observations/measurements of the natural world
• 2. inductive reasoning
• ideas (models) to explain the observations,
  search for patterns
• 3. hypothesis
• a testable statement that summarizes what is
  known so far

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• 4. predictions
• using the hypothesis to predict what
  observations should be seen
• verification (or not) of these predictions using
  more measurements or experiments simulating the
  real world
• 5. general theory
• after many years of testing and revising
  hypotheses, a theory may be earned - it still can
  be proven wrong but has not been yet.

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Example of the scientific method in real life
In 1821, William Redfield traveled through an
area of New England that had been recently hit by
a hurricane 1. He noticed that in S central
Connecticut all the fallen trees pointed NW, but
in NW Connecticut 70 miles away all the trees had
fallen pointing SE (observations) 2. He thought
that a hurricane must be a whirling vortex of
wind (hypothesis)  
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3. He researched in ships' logs for weather
information (many storms in many locations over
time) and plotted the wind patterns on maps
(verification of hypothesis) 4. Finally, he
published his theory that described cyclones as
having wind that blows in a spiral rotating
around a central axis, that moves
counterclockwise in the N hemisphere and
clockwise in the S hemisphere (mini-theory) Redfie
ld did not discover the whole of the big picture,
but a key part of it It took many years and the
work of many scientists to explain why this all
works, which we now know as the Coriolis effect.
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Basics of time and space on Earth
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Latitude
High Latitude Polar regions Low
Latitude Tropics
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Latitude
Latitude An angular distance north and south of
the equator
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Remember The largest circumference on Earth is
at the equator Any other latitude makes a
smaller circle (this will become important later
when we talk about Coriolis)
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• Examples of important latitudes
• Tropic of Cancer (23.5 degrees N) and Tropic of
  Capricorn (23.5 degrees S)
• they are the furthest parallels from the equator
  that still experience perpendicular rays of the
  sun at noon
• Arctic Circle (66.5 degrees N) and Antarctic
  Circle (66.5 degrees S)
• they are the furthest parallels from the poles
  to experience 24 hours of day in summer and 24
  hours of night in winter
• And of course the equator at 0 degrees

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Longitude
meridians are measured relative to an arbitrary
longitude called the prime meridian, which runs
through Greenwich, England
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Longitude
If you cut the Earth along any plane that also
cut through both the N and S poles, that would
give you a meridian
All lines of longitude are perpendicular to all
lines of latitude by definition
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• Latitude is easily measured by reference to fixed
  celestial objects
• the sun during the day and stars at night
• adjusting for the seasonal tilt of the Earth and
  for the time of day.
•  Longitude cannot be measured in the same way
  because the Earth is constantly rotating,
  changing the apparent location of the sun and
  stars

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• The solution to measuring longitude lies in
  knowing the exact time in two places at the same
  time
• Earth rotates 360 degrees in 24 hours 15
  degrees of longitude every hour
• therefore if you know the time at a
  fixed point on the surface (say, the port you set
  sail from)
• and the time at your location adjusted
  at local noon (when the sun is at its peak) every
  day as you travel
• then you can determine the difference in
  your longitude relative to that fixed point.
• This was hypothesized by Galileo in the early
  1600s, but could not be tested until technology
  advanced to the point when clocks remained
  accurate at sea in 1728.

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Time zones
each new day begins at 1201AM
Greenwich Mean Time (GMT)
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From the International Date Line, the new day
moves westward because Earth rotates from W to
E so time moves westward (Note AM stands for
ante meridiem or before noon, PM stands for post
meridiem or after noon) Imagine a giant Monty
Python-esque hand with a figure pointed to one
spot on Earth and focus your thought on that
spot. Sunrise is going to happen wherever that
finger is pointed - so as Earth moves from W to
E, the location of sunrise moves westward.
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Seasons of the Earth
(This is not the Earth, this is the sun.)
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• Perihelion closest at January 3
• 147,255,000 km (91,500,000 mi)
• Aphelion farthest at July 4
• 152,083,000 km (94,500,000 mi)

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Reasons for Seasons 

• Revolution
• Earth revolves around the Sun
• Voyage takes 365.25 days
• Earths speed is 107,280 kmph (66,660 mph)
• Rotation
• Earth rotates on its axis once every 24 hours
• Rotational velocity at equator is 1674 kmph (1041
  mph)

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Revolution and Rotation
Figure 2.13
The sun can only illuminate the side of Earth
facing it At the equator there is always 12
hours of day and 12 hours of night, but
everywhere else the length of day varies with the
seasons
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• Remember
• Earth's circumference is smaller as you move to
  the poles
• therefore the velocity of a point on the equator
  will be the greatest (1041 mph to make 1 rotation
  every 24 hours)
• at the poles the velocity is 0 mph
• at a point halfway between, the velocity is
  intermediate (40 degrees latitude, Columbus,
  Ohio, 798 mph)
• (this becomes important when we talk about
  Coriolis)

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Reasons for Seasons 

• Tilt of Earths axis
• Axis is tilted 23.5 from plane of ecliptic
• Axial parallelism
• Axis maintains alignment during orbit around the
  Sun
• North pole points toward the North Star (Polaris)
• Earth's sphericity
• Earth is not a perfect sphere but is squashed at
  the poles slightly
• This means there is a greater area near the poles
  that receives less solar energy than it would
  otherwise

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Tilt of the earths axis
SUN
Memphis
Equator
The equator on Earth is not in line with the
plane made by the Earth's orbit around the sun -
it is tilted by 23.5 degrees
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Axial Tilt and Parallelism
Parallelism - the axial tilt does not change as
the Earth rotates around the sun
Figure 2.14
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Length of day changes with seasons Examples
dawn and twilight Dawn is a period of diffused
light just before sunrise Twilight is diffused
light after sunset Determined by the amount of
atmosphere the light has to pass through before
it hits Earth's surface Equator experiences the
shortest periods (30-45 min) and the periods
increase as you move toward the poles, with up to
2.5 hours at 60 degrees latitude the poles
experience 7 weeks of dawn and 7 weeks of
twilight during the 6 months that the sun is
completely below the horizon, leaving only 2.5
months of total darkness.
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Annual March of the Seasons

• Winter solstice December 21 or 22
• N hemisphere is tilted away from sun time of
  northern winter
• sunlight passes through a greater amount of
  atmosphere and the insolation is diffused
• above the Arctic Circle (66.5 degrees) the sun
  remains below the horizon all day
• Vernal equinox March 20 or 21
• the circle of illumination passes through both
  poles and all points on Earth experience 12 hours
  of day and night
• above the Arctic Circle, the first sunrise of the
  new year occurs

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Annual March of the Seasons

• Summer solstice June 20 or 21
• N hemisphere is facing the sun radiation passes
  through the least amount of atmosphere all year
  and the sun is strongest
• above the Arctic Circle receives 24 hours
  daylight, called the midnight sun
• Autumnal equinox September 22 or 23
• circle of illumination again passes through both
  poles and all points on Earth experience 12 hours
  of day and night
• above the Arctic Circle the sun finally sets and
  will not be seen until the following vernal
  equinox in March

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Annual March of the Seasons
Figure 2.15