Lecture_08 - Lecture 8: Earth's Atmosphere 1.0 Thickness...

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Lecture 8: Earth’s Atmosphere 1.0 Thickness >82 km 2.0 Composition Nitrogen (N 2 ) 78%, oxygen (O 2 ) 21%, inert gases (Ar, Ne) 0.93%, carbondioxide (CO 2 ) 0.037%, helium (He) 0.0005%, methane (CH 4 ) 0.0002, hydrogen (H) 0.00005% Compared to other planets Terrestrial planets Venus almost entirely CO 2 . Atmospheric pressure 90 x that of earth’s. Mars almost entirely CO 2 . Atmospheric pressure is ~1% that of earth's. Jovian planets Jupiter, Saturn mostly H, He, and lesser amounts of CH 4 and ammonia (NH 3 ) 3.0 Pressure decreases exponentially with elevation At sea level ~1 bar top of Mt. Everest (8.8 km) ~0.32 bar Density decreases with elevation 1x10 -3 ->1x10 -12 @150km ½ of atmosphere lies below 5.6 km
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4.0 Temperature Range: 17 to –88 ºC with pauses and inversions. Mesopause ~ -88ºC @ ~80-85 km Stratopause ~ 0ºC @ ~47 km T ropopause ~ -57ºC @ ~10 km 5.0 Structure Thermosphere: ~85-600 km, temperature increase due to absorbtion of very short-wave high-energy solar radiation by atoms of o and n, molecule “travel distance” >1km. Mesosphere: ~47-80 km, negative temperature gradient, coldest part of atmosphere. Stratosphere: ~10-47 km, thermally stable, contains ozone layer 24-48 km, warming due to adsorption of ultraviolet ( uv) radiation . Troposphere: ~0-10 km, heated by sun’s energy at base, negative temperature gradient, well mixed, weather system, “to change”, molecule “travel space” one millionth of cm. 6.0 Evolution of Earth’s atmoshere First (primitive) atmosphere – 4.6-4.0 b.y. ago Composition - probably H 2 , He, NH 3 (ammonia) and CH 4 (methane) . Accretion (gravitational capture) of solar nebula, vaporization of incident comets. Evidence – atmosphere of jovian planets
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Heat from still molten crust and intense ultraviolet radiation present in early solar system broke apart nh 3 and ch 4 molecules, freeing h and n atoms. Being light in weight, h able to escape earth's atmosphere, leaving atmosphere depleted in H, enriched in N. Atmosphere completely
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Lecture_08 - Lecture 8: Earth's Atmosphere 1.0 Thickness...

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