GEO 102 Lecture 29 Outline of Last Lecture I Extinction Outline of Current Lecture II Major Mechanisms III Greenhouse Gases IV Glaciations V Causes and Consequences Current Lecture Major Mechanisms Solar output o Over long time scales Atmospheric content o Greenhouse gases like methane and carbon dioxide Orbital cycles o Controls 100 000 year glacial and monsoon cycles Solar output forcing faint young sun paradox o Young stars are weak o Only 70 of modern solar output Greenhouse Gases EM radiation is filtered by gases Incoming solar radiation is short wave o Passes through most atmospheric gases At night the earth radiates long wave radiation o Filtered and trapped by certain gases o Notably water methane and CO2 for some examples Greenhouse gases through time These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Addition of O2led to oxidation of methane at the end of Archean o First known global ice house Weathering in later Proterozoic led to snowball Earth Change in carbon cycle in Carboniferous led to ice house Ice House vs Greenhouse Earth was usually warmer than now 5 major and 1 minor ice house Each seems to have been caused by changes to the atmosphere and greenhouse gases o Within each there were higher frequency climate shifts Huronian Glaciation Oldest known event Glacial impact in rock record Caused by addition of O2 to atmosphere Oxidized methane to produce CO2 CO2 is a weaker greenhouse gas so earth cooled to ice house since the sun was still faint then Snowball Earth Late Proterozoic glaciation Largest one ever Ice was nearly or entirely frozen over repeatedly Causes and Consequences Low greenhouse gas levels with a weak sun Perhaps driven by equatorial weathering Evidence in chemistry and glacial rocks at sea level in the tropics Huge impact on early life o Life isolated into small microcosms o Changed ocean chemistry Later Atmospheric Glaciations Ordovician Glaciation o Cause is complex and poorly understood o Greenhouse related Late Paleozoic Glaciation o Change in C cycle related to land plant evolution Mid Mesozoic Glaciation o Small ice age Cenozoic Glaciation o Related to tectonic and oceanic CO2 decreases
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