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

nebula of the Sun (mainly H2, He);♦II - outgassing of the planet (volcanoes, geysers,…);

formation of an ocean (perhaps?); material from meteoritesand comets;

♦III – evolution of the atmosphere due to the presence of lifeand 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’satmosphere from the Earth’s geological records and by studyingother planets.• The role of the atmosphere: protection from UV and cosmicrays, shields us from meteorites, decreases the day/nighttemperature variations…

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.

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

Life: abundanceof oxygen,human impact

NANAStage III:Life forms

Yes, H2O, CO2…Yes: H2O, CO2 …Not importantStage II:Outgassing

Yes but lostdue to weakgravity

Yes but lostdue to weakgravity

YesStage I:H2 and He

EarthTerrestrials:Venus, Mars

Gas Giants:Jupiter,Saturn, …

Planets:

The Terrestrial PlanetsMercury PlutoEarth MarsVenus

Distance 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

480T=15 C

-60

-110

-190

-215-225

-235

Main components - CO2 CO2N2, O2 CH4

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

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, 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

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

Perm

anen

t ga

sses

Variab

le ga

sses

1%=1/100 1ppm=1/1000,000

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

• Carbon dioxide: CO2

♦Input: plant decay,exhalation, fossil fuels,deforestation.

♦Output: photosynthesis,dissolves in the ocean

♦Greenhouse gas, steadilyincreases with time.

CO2

• Ozone: O3

♦O3 in the stratosphere (25 km)shields the UV light;

♦At the ground level it results inphotochemical smog.• Dust, aerosols and pollutants: also

can have a greenhouse effect

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 ρ:♦ 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

W

r

Atmospheric pressure

Atmospheric pressure and density decrease with altitude exponentially!!!

Vertical Structure of the Earth’sAtmosphere

99.9%

90%

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.

Atmospheric layers

• Mixing:♦Homosphere:

• well mixed,• the chemical

composition isconstant.

♦Heterosphere:• no turbulence and

mixing,• diffusive separation

of gasses• Ionization:♦Ionosphere: part of the

atmospheric gas is ionizedthrough photo ionizationor impact ionization.