the earth and its atmosphere: 1.chemical composition and 2. vertical structure
TRANSCRIPT
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The Earth and Its Atmosphere:
1.Chemical composition and 2. Vertical structure
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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 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
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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
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The Terrestrial Planets
Mercury PlutoEarth MarsVenusDistance AU.
Radius RE.
Density.
Gravity.
Rotational period
Orbital period.
Obliquity
1
1
1
23.4
9.78
5.5
24
1
0.39
0.055
0.38
0
3.62
5.43
1407
0.24
0.72
0.815
0.95
2.7
8.57
5.24
5832
0.6
1.5
0.1
0.53
25
3.7
3.94
24.6
1.88
39.4
0.0025
0.176
62
0.3
2
153
247
Mass ME.
260
480
T=15 C
-60
-110
-190
-215-225
-235
Main components
- CO2CO2N2, O2 CH4
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The Giant Planets
Jupiter NeptuneEarth UranusSaturnDistance AU
Radius RE
Density
Gravity
Rotational period
Orbital period
Obliquity
1
1
1
23.4
9.78
5.5
24
1
5.2
318
11
3
22.9
1.31
10
11.9
9.5
94.5
9.5
27
9
0.69
10
29.5
19.2
14.5
4
98
8.7
1.29
18
84
30
17
3.9
30
11
1.64
19
165
Mass ME
Main components
N2, O2 H2, He H2,He,CH4 H2, HeH2, He
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Neptune’s atmosphere: 80% H2, 19% He, 1% CH4
Uranus’ atmosphere: 83% H2, 15% He, 2% CH4
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Sample test questions
•Since the turn of this century, CO2 in the atmosphere has:a. been increasing in concentrationb. been decreasing in concentrationc. remained at about the same
concentration from year to yeard. disappeared entirely
•The earth's first atmosphere was composed primarily of:a. carbon dioxide and water vaporb. hydrogen and heliumc. oxygen and water vapord. argon and nitrogen
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The Earth’s Atmospheric Composition Today
Nitrogen (N2) 78.08%
Oxygen (O2) 20.95%
Argon (Ar) 0.93%
Nobel gasses (Ne, He, H2, Xe) <0.003%
Water vapor (H2O) 0-4 %
Carbon dioxide (CO2) 0.037 %
Methane (CH4) 1.7 ppm
Nitrous Oxide (N2O) 0.3 ppm
Ozone (O3) 0.04 ppm
Particles (dust …) <0.15 ppm
Chlorofluorocarbons (CFCs) 0.0002 ppm
Permanent gasses
Variable gasses
1%=1/100 1ppm=1/1000,000
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Important gas components
•Nitrogen: N2
♦ Input: decaying plant and animal products ♦ Output: biological processes (soil bacteria, plankton)
•Oxygen: O2
♦ Input: photosynthesis;♦ Output: decay of organic matter, production of oxides, breading (CO2).
•Water vapor: H2O
♦ Input: evaporation♦ Output: condensation♦ A highly variable greenhouse gas, not visible, results in large latent heat.
IN OUT
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•Carbon dioxide: CO2
♦ Input: plant decay, exhalation, fossil fuels, deforestation.
♦ Output: photosynthesis, dissolves in the ocean
♦ Greenhouse gas, steadily increases with time.
CO2
•Ozone: O3
♦ 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
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Mass,Weight, Density, Pressure
•Mass M: ♦ property of matter,♦ SI unit: kg. Other units: 1kg=1000 g, 1 lb=450
g
•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 : ♦ 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
Wr
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Atmospheric pressure
Atmospheric pressure and density decrease with altitude exponentially!!!
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Vertical Structure of the Earth’s Atmosphere
99.9%
90%
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Atmospheric layers(according to the temperature)
•Troposphere: ♦ The temperature T decreases with height about 6.5 K/km.
♦ 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.
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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.