1. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Yo, who turned up the

2. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan QUIZ! Last Updated: June 1, 2016 On a scale of 0 - 10: The ozone hole and global warming are related. 0 No way! 10 You Betcha! 5 Coward

3. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Driving Questions 1. The composition of the atmosphere has changed quite naturally in the past. How did THAT happen? 2. How does our present atmosphere’s composition influence the flow of energy to and from the Earth’s surface? 3. The thermal characteristics of our atmosphere vary with altitude. How and Why? Today’s Issues: Last Updated: June 1, 2016

4. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Comparison with other Planets The composition of the earth’s atmosphere is markedly different from that of our neighboring planets. Nonetheless they originated from the same process. Atmospheric Composition

5. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Stages of Atmospheric Formation 1.Origin In formative years the atmosphere was composed of H and He. 2.Chemical/ pre-biological era Atmosphere formed from volcanic outgassing lead dominated by water vapor, CO 2, SO 2 and others. 3.Microbial era Initial O 2 formed through photolysis allowed ozone layer, early microbes emitted O 2 as waste product. 4.Biological era Simultaneous decrease in atmospheric CO 2 and the increase in O 2 due to life processes. Atmospheric Composition

6. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Initial Atmosphere Composed Largely of Water Vapor and Carbon Dioxide The atmosphere grew from the outgassing of the cooling planet. Assuming that the gases we presently observe were also released by early volcanoes the atmosphere would be made of water vapor (H 2 O), carbon monoxide (CO), carbon dioxide (CO 2 ), hydrochloric acid (HCl), methane (CH 4 ), ammonia (NH 3 ), nitrogen (N 2 ), & sulfur gases. The atmosphere was reducing (no free oxygen). Volcanic Origins Gas plume as lava enters the Pacific Ocean at Kilauea volcano, Hawaii. Photo copyrighted by Paul J. Buklarewicz.

7. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Slow removal of Carbon Dioxide and Water Vapor through Precipitation and Chemical Weathering As planet cooled through release of long-wave radiation the temperature fell to a point that water vapor could condense to liquid water. The ensuing precipitation removed water to the surface and carried away soluble gasses like carbon dioxide and sulfur dioxide. The carbon became sequestered in ocean sediment through chemical weathering. oWater reacts with CO 2 to produce carbonic acid. oCarbonic acid reacts with Calcium and Magnesium silicate rocks to yield Calcium Carbonate (CaCO 3 = limestone) or Magnesium Carbonate (MgCO 3 = Dolomite) and Silicon Oxide (SiO 2 ). Example: CaSiO 3 + CO 2  CaCO 3 + SiO 2 Weathering Removes CO 2

8. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan The amount of water the atmosphere can hold is a function of its temperature. Cooling Removes Water Vapor Clausiuys-Clapyron Relationship

9. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan The initial oxygen formation lead to feedbacks that further enhanced the formation of oxygen Consequences of Oxygen Build-Up Some atmospheric oxygen formed through photodissociation of water vapor: Some formed as waste product os photosynthetic autotrophs. Development of an ozone (O 3 ) layer, which absorbs harmful UV radiation and eventaully allowed life on land. End of banded iron formations which only formed in low O 2 Beginning of deposition of red beds - iron oxides Development of the eukaryotic cell (~2.1 Ga)

10. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Oxygen formed was at first sequestered in oxidation of iron but transition to aerobic life and photosynthesis lead to build-up of atmospheric oxygen. Arrival of Oxygen

11. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Oxygen concentrations are balanced between photosynthetic formation by autotrophs and respiratory destruction by heterotrophs and decay. Arrival of Oxygen

12. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Changes in CO2 We know the concentration of some gases have changed significantly over time. Changes in Atmospheric Composition Geochemically inferred. NOW

13. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Units One way to express relative concentrations of gases in the atmosphere is to compare their percentages by volume. A second way is to express their parts per million by volume. Atmospheric Composition EXAMPLES: N 2 78.08%780,800 ppm O 2 20.95%209,500 ppm Ar 0.93% 9,300 ppm CO 2 0.036% 360 ppm

14. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Who Let the CO 2 Out? Today’s atmospheric composition is dominated by Nitrogen and Oxygen, neither of which were dominant in outgassing and carbon dioxide has fallen to trace levels. Atmospheric Composition

15. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Blackbody Radiation Selective Absorbers An object that absorbs all radiation incident upon it is called a “blackbody.” Radiative Properties Some gases only absorb in selected wavelengths dictated by their atomic structure. In the atmosphere so-called “greenhouse gases” are “selective absorbers” that absorb in the wavelengths of Earth emissions. E =  T 4 max = C/T

16. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Energy Balance Ultimately the selective absorbers influence the flow (flux) of energy to and from the earth’s surface. Energy Balance Controls Temperature

17. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Pressure Temperature Force exerted per unit area. In most sciences the standard unit of measure is the pascal (Pa), but in meteorology either millibar (1 mb = 100 Pa) or inches of Mercury (in Hg = 3386 Pa) are used. A measure of the average kinetic energy of the molecules comprising a substance. The Structure of the Atmosphere

18. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Pressure Temperature Force exerted per unit area. In most sciences the standard unit of measure is the pascal (Pa), but in meteorology either millibar (1 mb = 100 Pa) or inches of Mercury (in Hg = 3386 Pa) are used. A measure of the average kinetic energy of the molecules comprising a substance. The Structure of the Atmosphere

19. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan The thermosphere is the fourth layer of the Earth's atmosphere and is located above the mesosphere. The air is really thin in the thermosphere. A small change in energy can cause a large change in temperature. For this reason the temperature of the thermosphere is very sensitive to solar activity. When the sun is active, the thermosphere can heat up to 1,500°C or higher! The Earth's thermosphere also includes the region of the atmosphere called the ionosphere. The ionosphere is a region of the atmosphere that is filled with charged particles. The high temperatures in the thermosphere can cause molecules to ionize. This is why an ionosphere and thermosphere can overlap. Thermosphere

20. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Thermosphere

21. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan In the Earth's mesosphere, the air is relatively mixed together and the temperature decreases with altitude. The atmosphere reaches its coldest temperature of around - 90°C in the mesosphere. This is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere. Mesosphere

22. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan In the Earth's stratosphere, the temperature increases with altitude. On Earth, ozone causes the increasing temperature in the stratosphere. Stratosphere Ozone is concentrated around an altitude of 25 kilometers in the “ozone layer.” The ozone molecules absorb dangerous kinds of sunlight, which heats the air around them.

23. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan The troposphere is the layer in contact with the Earth’s surface and hence its temperature structure is predicated by energy transmitted to and from the surface. Troposphere

24. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Troposphere The troposphere is the layer in contact with the Earth’s surface and hence its temperature structure is predicated by energy transmitted to and from the surface.

25. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Summary Driving Questions 1. The composition of the atmosphere has changed quite naturally in the past. How did that happen? Keywords: Outgassing Chemical weathering Photosynthesis Photolysis Oxidation

26. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Summary Driving Questions 2. How does our present atmosphere’s composition influence the flow of energy to and from the Earth’s surface? Keywords: Selective absorbers Longwave radiation Shortwave radiation

27. Evolution of the Atmosphere: Structure and Composition Composition Structure Summary Evolution Issues ©2001, Perry Samson, University of Michigan Summary Driving Questions 3. The thermal characteristics of our atmosphere vary with altitude. How and Why? Keywords: Troposphere Weather Stratosphere Ozone Layer Mesosphere Thermosphere Ionosphere, Aurora