Last LectureOutlineLectureEES 1040 1st Edition Lecture 10Last Lecture Prokaryotes vs. EurkaryotesOutlineI. The Greenhouse EffectII. AtmosphereIII. The Snowball Earth HypothesisLectureI. The Greenhouse EffectA. Green Houses1. Direct sunlight passes into greenhouse2. Sunlight strikes surfaces3. When sunlight is reflected, much of it is scattered as longer wavelength infra-red light4. Infrared-wavelength light can’t pass through the glass as easily5. Much of it is trapped in greenhouse and converted to heatB. Exactly the same principle explains how Earth’s surface is heatedC. Surface is surrounded by gases in atmosphere which act like the glass in a greenhouse1. “greenhouse gases”a. Ex. methane, CO2D. CO2 +H2O photosynthesis sunlgight CH2O + O2E. Resporation energy for metabolismII. AtmosphereA. O2 CO2B. Animal respiration PhotosynthesisC. Decomposer respiration “fixed” in the structures of the plantD. K Dies and buriedE. K C buried in sediments (“sequester”)F. K weathering and erosionG. Usually the system is in balanceH. Burial of organic C ~= weathering erosionI. BUT, increased burial of organic C:1. Decrease CO2 atmosphere2. Decrease greenhouse warmingJ. Remember, photosynthesizers prefer 12C1. 12C/13C ratioIII. The Snowball Earth HypothesisA. Brian Harland (Cambridge) 19641. Neoproterozoic glacial deposits on every continenta. 600-700 MAB. Mikhail Budyko (Leningrad)1. Early climate models2. Albedo:a. % of sunlight of sunlight reflected from Earth’s surfaceC. As glaciation grows, albedo provides positive feedback1. More glaciers higher Albedo colder more glaciers, etc.D. Estimated “critical point” 30 degrees North and South (tropics)E. Joe Kirschrink (Cal Tech) 1980s1. Where are the glacial deposits2. Paleomagnetisma. Within a few degrees of the equator F. Banded Iron formations1. Gone for over a BA2. Suddenly back and associated with glacial deposits G. Paul Hoffman and Dan Schrag (Harvard)1. “Cap Carbonates“a. Glacial deposits are immediately capped by dolostone carbonatesb. All around the world, even if no other carbonatesc. “Reversal mechanism”- Mid oceanic ridges- Volcanoes ii. Insanely high CO2iii. Revers Albedo and extreme greenhouseiv. Water vapor is a greenhouse gas- More positive feedback for deglaciationv. Temps soar in a few hundred years - -40 Celsius +50 Celsius vi. Intense hydrological cycle- Pounding rainvii. Carbonic acid rainviii. Intense chemical weathering of exposed landix. Sudden, intense precipitation of carbonate in the world’s shallow oceans2. C
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