The Origin of the Atmosphere Intro to Atmospheric Physics 08/26/15 Dr. Chris Moore cmoore@dri.edu

http://www.iup.uni-heidelberg.de/institut/studium/lehre/ Atmosphaerenphysik/WS1011/01_Physics_of_the_Atm-WS2010_Intro_tl.pdf

How did our atmosphere develop?

Geologic time scales Understanding the evolution of the atmosphere involves looking at the development of Earth and planets in general The development of the Earth’s atmosphere is still a hot topic of research with new breakthroughs happening all the time There are two processes governing the development of Earth and the early atmosphere: 1) Accretion 2) Outgassing http://web.eng.ucsd.edu/~pcabrales/research2.html

Accretion Earth formed from the Solar Nebula (swirling disk of interstellar dust and hydrogen surrounding the earliest form of the sun) about 4.6 billion years ago Iron and nickel core forms first due to cooling and they solidify at the highest temperature Then continued collisions and differentiation separates areas due to different densities http://facweb.bhc.edu/academics/science/harwoodr/geog102/study/origin.htm

Outgassing Process where gases trapped in interior get released Early oceans of hot magma existed on the surface overturning planetary material Volatile gases released from interior CO2 CO H2 N2 H2O Gases remained trapped in a surface layer by gravity Still occurs today through volcano eruptions Following accretion into a large planet-sized object during the early years of the solar system, Earth’s first major atmosphere was formed by the release of gases trapped in the restless interior, a process that still goes on today in volcanoes (Figure 8.1). These early years are marked by swirling oceans of hot magma that no longer exists today on any planet in our solar system. Extreme volcanism in Earth’s early history occurred in response to this energetic motion of then-molten mantle material. As planetary material violently overturned, volatile gases from the interior, especially Carbon dioxide (CO2), Carbon monoxide (CO), Hydrogen (H2), Nitrogen (N2) and water vapor (H2O), were released, and accumulated in a gaseous surface layer that was trapped by gravitational forces. Radiation from the nearby Sun swept lighter gases as H and He away, leaving only heavier molecules in this early atmosphere. Chemical reactions in the hot surface layer formed other simple atmospheric compounds, such as methane (CH4) and ammonia (NH3). While far less abundant, the latter compounds are highlighted as they are key components of amino acids, which are the fundamental building blocks of life’s proteins. Note also that Oxygen (O2), key to the survival of many forms of modern life, was not present in the early atmosphere. http://www.globalchange.umich.edu/gctext/Inquiries/Inquiries_by_Unit/Unit_8.htm

Early Atmosphere The early atmosphere was devoid of oxygen (reducing) There is still debate about when the current oxidizing atmospheric composition developed Traditionally this was thought to have occurred around 400 million years ago driven entirely by O2 produced from photosynthetic activity

Recent developments Atmosphere as we know it (oxidizing) may have actually started forming 4 billion years ago This has large implications for our understanding of the development of life as the current understanding is that life developed during the reducing atmospheric conditions Very interesting area of on-going research…

Evolution of Carbon http://butane.chem.uiuc.edu/pshapley/Environmental/L29/2.html

Biological Evolution The evolution of the current atmosphere is strongly linked to the evolution of plants to produce the oxygen 13.2: Postulated rise in atmospheric oxygen over geologic time, and its relationship to ice ages (blue bars) and biospheric evolution. If the step-like rises in oxygen were rapid, consequent destruction of atmospheric methane (a powerful and potentially major greenhouse gas in the early atmosphere) could account for the Makganyene and Sturtian snowball earths. If the oxygen rises were slow (millions of years), methane destruction might be offset by CO2 rise modulated by silicate weathering feedback. The Marinoan snowball earth, coming <75 Myr after the Sturtian, is more difficult to attribute to methane destruction, requiring a methane-oxygen see-saw. http://www.snowballearth.org/week13.html

http://www.iup.uni-heidelberg.de/institut/ studium/lehre/Atmosphaerenphysik/WS1011/ 01_Physics_of_the_Atm-WS2010_Intro_tl.pdf

http://www.iup.uni-heidelberg.de/institut/ studium/lehre/Atmosphaerenphysik/WS1011/ 01_Physics_of_the_Atm-WS2010_Intro_tl.pdf

Atmospheric “Floors” Characteristic temperature profiles in the layers http://www.windows2universe.org/earth/Atmosphere/layers_activity_print.html

Tropopause Can be defined by temperature changes Can also be defined chemically Lower stratosphere has higher ozone and lower water vapor

hectopascal A

Atmospheric Pressures It is often easiest to represent the atmosphere via pressure (isobaric) to make equations either to deal Therefore, it’s good to get used to the approximate pressures at different heights

Atmospheric Chemistry

No. of Different Species

Hg biogeochemical cycle From www.mfe.govt.nz

Mercury in the Arctic Fragile Arctic ecosystems Methyl mercury is a neurotoxic pollutant and accumulates in living organisms Piscivorous fish Polar Bears Whales Seals Muktuk Valera et al. 2012 NeuroToxicology; Tian et al. 2011 Environment International

Mercury and Ozone in the Arctic Surface Layer From Steffen et al. 2008 ACP

Quiz! Thanks to Thomas Leisner at IUP (Institute of Environmental Physics) Heidelberg for the many slides