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 H 2, 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…

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 8 th Ave from 34 th St. to 22 nd 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: H 2 and He YesYes but lost due to weak gravity Stage II: Outgassing Not importantYes: H 2 O, CO 2 … Yes, H 2 O, CO 2… Stage III: Life forms NA Life: abundance of oxygen, human impact

The Terrestrial Planets Mercury PlutoEarthMarsVenus Distance AU. Radius R E. Density. Gravity. Rotational period Orbital period. Obliquity Mass M E T=15 C Main components - CO 2 N 2, O 2 CH 4

The Giant Planets Jupiter NeptuneEarthUranusSaturn Distance AU Radius R E Density Gravity Rotational period Orbital period Obliquity Mass M E Main components N 2, O 2 H 2, HeH 2,He,CH 4 H 2, He

Neptune’s atmosphere: 80% H 2, 19% He, 1% CH 4 Uranus’ atmosphere: 83% H 2, 15% He, 2% CH 4

Sample test questions Since the turn of this century, CO 2 in the atmosphere has: a.been increasing in concentration b.been decreasing in concentration c.remained at about the same concentration from year to year d.disappeared entirely The earth's first atmosphere was composed primarily of: a.carbon dioxide and water vapor b.hydrogen and helium c.oxygen and water vapor d.argon and nitrogen

The Earth’s Atmospheric Composition Today Nitrogen (N 2 ) 78.08% Oxygen (O 2 ) 20.95% Argon (Ar) 0.93% Nobel gasses (Ne, He, H 2, Xe) <0.003% Water vapor (H 2 O) 0-4 % Carbon dioxide (CO 2 ) % Methane (CH 4 ) 1.7 ppm Nitrous Oxide (N 2 O) 0.3 ppm Ozone (O 3 ) 0.04 ppm Particles (dust …) <0.15 ppm Chlorofluorocarbons (CFCs) ppm Permanent gasses Variable gasses 1%=1/1001ppm=1/1000,000

Important gas components Nitrogen: N 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 (CO 2 ). Water vapor: H 2 O ♦ Input: evaporation ♦ Output: condensation ♦ A highly variable greenhouse gas, not visible, results in large latent heat. IN OUT

Carbon dioxide: CO 2 ♦ Input: plant decay, exhalation, fossil fuels, deforestation. ♦ Output: photosynthesis, dissolves in the ocean ♦ Greenhouse gas, steadily increases with time. CO 2 Ozone: O 3 ♦ O 3 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 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/s 2 ♦ SI unit: kg m/s 2 -> N g(Mars)= 3.7 m/s 2 Density  : ♦ mass per unit volume: density = mass / volume ♦ SI unit: kg/m 3, Other: g/cm 3 Pressure p: ♦ p= force/area ♦ SI units: Pa=N/m 2, 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. ♦ 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; ♦ O 3 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.