Geology 305 Notes for October 17
Geology 305 Notes for October 17 Geology 305
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This 2 page Class Notes was uploaded by Brandon Cook on Tuesday October 18, 2016. The Class Notes belongs to Geology 305 at University of South Carolina - Columbia taught by Dr. Susan Lang in Fall 2016. Since its upload, it has received 6 views. For similar materials see Earth Systems Through Time in Geology at University of South Carolina - Columbia.
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Date Created: 10/18/16
Back From Fall Break Faint Young Sun What is paradoxical about F Y S ? What evidence is there for liquid water on Early Earth? What could explain the faint young sun paradox? Stars including sun becomes brighter over its life Young Stars are fainter than older stars In Archean sun was ¼ less bright about 233 K now at 256 K With the same amount of GHG the earth would be frozen before 2 bya Pillow Basalts require liquid water to form common in Archean greenstone belt 3.8 bya other evidence is sedimentary structures occurred too Delta O18 zircons indicate the presence of liquid water as early as 4.4 bya Many Archean rocks are sediments of deep water origin, cherts halites and gypsum Pillow basalts and O18 zircons Also no evidence of glaciation until 2.3 bya Earth temperature between 0-100C for the first 2.2 bya To warm planet enough to prevent frozen water would require 100-1000x more CO2. High CO2 results in siderite in the soils Absence of siderite in Archean paleosoils to account for it Record from Archean indicate raindrops are large indicates air density was similar to present day Suggest very high CO2 level unlikely Evidence paleobarometers suggests CO2 unlikely to be that high Methane is 8x stronger GHG Early Earth was oxygen free CH4 resulted in a brown hazy sky Could have provided sufficient global warming without high CO2 levels Methane can only happen in the absence of oxygen Microbes formed methane (methanogenesis) Oxygen is present- form water Present day 0.7 ppmv High methane levels lead to an organic haze which reflects sunlight Very high CH4 levels unlikely Magnetite in Archaean chemical sediments CO2 and H2 mixing ratios nots significantly different than present Why? Early earth may had much lower albedo than today Water has a lower albedo than land surface Fewer clouds with fewer Cloud condensation nuclei CCN Presently CCN formed due to plants and algae Early earth was combination of higher GHG and lower albedo than present day Earth
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