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The Earth and Its Atmosphere:
1.Chemical composition and
2. Vertical structure
RECAP
• Definition
of an atmosphere: the gas surrounding a
planet/satellite/comet/…
• Origin
of the atmosphere. Three stages:
♦ I - gravitational capture of the gasses in the proto planetary
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nebula of the Sun (mainly H2, He);
♦ II - outgassing of the planet (volcanoes, geysers,…);
formation of an ocean (perhaps?); material from meteorites
and comets;
♦ III – evolution of the atmosphere due to the presence of life
and human activity.
The early atmosphere of the Earth is very different from the
atmosphere today!
We learn about the formation and the evolution of the Earth’s
atmosphere from the Earth’s geological records and by studying
other planets.
The role of the atmosphere: protection from UV and cosmic
rays, shields us from meteorites, decreases the day/night
temperature variations…
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Planets in the Solar System
Definition of a planet: a celestial body which
♦ is in orbit around the sun
♦ has sufficient mass for its self-gravity to
overcome rigid body forces so that it assumes a ...
nearly round shape
♦ has cleared the neighborhood around its orbit
Pluto disqualified since orbit overlaps with Neptune's.
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The Gainesville Solar Walk
Along NW 8th Ave from 34th St. to 22nd St.
Alachua Astronomy Club (AAC) says
♦ It is the AAC's judgement that Pluto is here to stay and any future
modifications of the Solar Walk should be additions or improvements
(Approved by the AAC Board, 2006 Sept. 5)
Future enhancement: additional benches, an asteroid rock
garden, nighttime lighting, enhanced landscaping
Origin of the atmospheres
Planets:
Gas Giants:
Jupiter,
Saturn, …
Terrestrials:
Venus, Mars
Earth
Stage I:
H2 and He
Yes
Yes but lost
due to weak
gravity
Yes but lost
due to weak
gravity
Stage II:
Outgassing
Not important
Yes: H2O, CO2 … Yes, H2O, CO2…
Stage III:
Life forms
NA
NA
Life: abundance
of oxygen,
human impact
The Terrestrial Planets
260
Mercury Venus Earth Mars
0.39
0.72
1
1.5
-235
Mass ME.
480
T=15 C
Pluto
39.4
0.055
0.815
1
0.1
0.0025
0.38
0.95
1
0.53
0.176
5.43
5.24
5.5
3.94
2
Gravity. 3.62
8.57
9.78
3.7
0.3
0
2.7
23.4
25
62
0.24
0.6
1
1.88
247
1407
5832
24
24.6
153
-
CO2
N2, O2
CO2
CH4
-60
Density.
-110
-190
-225
-215
The Giant Planets
Earth Jupiter Saturn Uranus Neptune
1
5.2
9.5
19.2
30
Mass ME 1
318
94.5
14.5
17
11
9.5
4
3.9
Density 5.5
1.31
0.69
1.29
1.64
Gravity 9.78
22.9
9
8.7
11
23.4
3
27
98
30
1
11.9
29.5
84
165
24
10
10
18
19
1
N2, O2
H2, He
H2, He H2,He,CH4 H2, He
Neptune’s atmosphere: 80% H2, 19% He, 1% CH4
Uranus’ atmosphere:
83% H2, 15% He, 2% CH4
Sample test questions
• Since the turn of this century, CO in the atmosphere has:
a.
b.
c.
d.
2
been increasing in concentration
been decreasing in concentration
remained at about the same
concentration from year to year
disappeared entirely
• The earth's first atmosphere was composed primarily of:
a.
b.
c.
d.
carbon dioxide and water vapor
hydrogen and helium
oxygen and water vapor
argon and nitrogen
Permanent gasses
The Earth’s Atmospheric Composition Today
Nitrogen (N2)
78.08%
Oxygen (O2)
20.95%
Argon (Ar)
Nobel gasses (Ne, He, H2, Xe)
Variable gasses
Water vapor (H2O)
0.93%
<0.003%
0-4 %
Carbon dioxide (CO2)
0.037 %
Methane (CH4)
1.7 ppm
Nitrous Oxide (N2O)
0.3 ppm
Ozone (O3)
Particles (dust …)
0.04 ppm
<0.15 ppm
Chlorofluorocarbons (CFCs) 0.0002 ppm
1%=1/100
1ppm=1/1000,000
Important gas components
• Nitrogen: N
IN OUT
2
♦ Input: decaying plant and animal products
♦ Output: biological processes (soil bacteria, plankton)
• Oxygen: O
2
♦ Input: photosynthesis;
♦ Output: decay of organic matter, production of oxides,
breading (CO2).
• Water vapor: H O
2
♦ Input: evaporation
♦ Output: condensation
♦ A highly variable greenhouse gas, not visible, results in large
latent heat.
• Carbon dioxide: CO
2
♦ Input: plant decay,
exhalation, fossil fuels,
deforestation.
♦ Output: photosynthesis,
dissolves in the ocean
♦ Greenhouse gas, steadily
increases with time.
CO2
• Ozone: O
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3
♦ O3 in the stratosphere (25 km)
shields the UV light;
♦ At the ground level it results in
photochemical smog.
Dust, aerosols and pollutants: also
can have a greenhouse effect
Mass,Weight, Density, Pressure
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Mass M:
♦ property of matter,
♦ SI unit: kg. Other units: 1kg=1000 g, 1 lb=450 g

W
Weight
:
♦ a force, has a magnitude and direction (vector).
♦ weight = mass x gravity
g(Earth)= 9.78 m/s2
♦ SI unit: kg m/s2 -> N
g(Mars)= 3.7 m/s2
Density r:
♦ mass per unit volume: density = mass / volume
♦ SI unit: kg/m3, Other: g/cm3
Pressure p:
♦ p= force/area
♦ SI units: Pa=N/m2, Other: 1bar=100 Pa
Atmospheric pressure
Atmospheric pressure and density decrease with altitude exponentially!!!
Vertical Structure of the Earth’s
Atmosphere
99.9%
90%
Atmospheric layers
(according to the temperature)
• Troposphere:
♦ The temperature T decreases with height about 6.5 K/km.
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♦ Well mixed as a result of turbulence and convection;
♦ Weather phenomena
Tropopause:
♦ isothermal (T constant)
♦ located 8-15 km above the ground.
Stratosphere:
♦ Increasing temperature;
♦ O3 layer at 25 km altitude;
♦ The atmosphere is very stable.
Stratopause: T=const
Mesosphere:
♦ T is decreasing: effective cooling through IR emission.
Mesopause: the coldest region on Earth.
Thermosphere: fast T increase. Diffusive separation of gasses.
Atmospheric layers
• Mixing:
♦ Homosphere:
well mixed,
the chemical
composition is
constant.
♦ Heterosphere:
no turbulence and
mixing,
diffusive separation
of gasses
Ionization:
♦ Ionosphere: part of the
atmospheric gas is ionized
through photo ionization
or impact ionization.
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