Lecture 4.5 Notes

Lecture 4.5 Notes - I. EARLY EARTH AND THE ORIGIN AND...

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I. EARLY EARTH AND THE ORIGIN AND DIVERSIFICATION OF LIFE 14.1 Formation and Early History of Earth Formation 4.5 bya First fossil evidence of microbial life in rocks from 3.86 bya 14.2 Origin of Cellular Life Surface origin hypothesis: unlikely due to hostile and unstable conditions (e.g. – high levels of UV radiation prior to ozone shield,) Subsurface hypothesis o Hydrothermal springs on ocean floor – less hostile more stable conditions o Steady abundant supply of reduced inorganic compounds (H 2 and H 2 S) o Montmorillonite clays – catalyzed formation of amino acids, simple peptides, sugars, nitrogenous bases and nucleotides. The RNA world o Evolution of self-replicating RNAs at reactive surfaces Lipid membranes and cellular life o Entrapment of self-replicating nucleic acids by lipid vesicles independence from external environment and autonomous compartmentalization. o Evolution of LUCA Early metabolism o Anoxic conditions of early earth and absence of abundant sources of reduced carbon exclusively anaerobic and autotrophic life forms Possibly reflected in autotrophic hyperthermophiles such as Aquifex and counterparts from the Archaea that branch near the root of the evolutionary tree o Possible scheme for generation of proton motive force based on oxidation of H 2 and reduction of sulfur by primitive hydrogenase involving elements known to be abundant on early earth. 14.3 Microbial Diversification: Consequences for Earth’s Biosphere Metabolic diversification Presence of LUCA as early as 4.25 bya Divergence of Archaea and Bacteria – 4.1-3.9 bya O 2 -evolving photosystem by cyanobacteria - 2.7 bya the waste product that changed the world The rise of oxygen o 2.7 – 2.4 bya: oxidation of vast stores of ferrous iron in the oceans then rise in levels of atmospheric O 2 New metabolisms and the ozone shield o Enormous consequences of oxygenic photosynthesis: change in atmosphere from anoxic to oxic the ozone shield makes the surface inhabitable for carbon-based life forms tremendous energy efficiency afforded by aerobic respiration development of larger population sizes allows faster evolution rapid radiation of the new eukaryotic domain….
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Lecture 4.5 Notes - I. EARLY EARTH AND THE ORIGIN AND...

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