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Early Earth and the Origins of Life Why do we care? How old do you think Life is? Early Earth and the Origins of Life Lecture overview: -formation of the solar system and Earth -conditions on early Earth -theories concerning the origin of life on Earth -geologic evidence for earliest life on Earth The Geologic Timescale LIFE Life!?! Planetary disk with thanks to L. T. Elkins-Tanton, JPL NASA/JPL Ca-Al inclusions in carbonaceous chondrites: 4.5672±0.0006 Ga (billion years ago) Linked solidification and cooling processes Elkins-Tanton magma oceans at first… Formation of the Moon: 4.53Ga Moon forms from debris of a collision between a Mars-sized body and Earth Animation of moon formation, courtesy of Joe Tucciarone The Archean Earth System Archean: 4.03 to 2.5 Ga (Ga=billion years ago) • Late Heavy Bombardment (4.1 to 3.8 Ga) • Atmosphere: hardly any molecular oxygen (O2); appears at ~2Ga earliest life probably anearobic! • UV radiation (no ozone shield) earliest life probably underwater! • CO2 and CH4 -rich atmosphere • Likely warm surface conditions (80o to 45oC) • High rate of heat transfer from core to surface, possible thin crust, plate tectonics just being established w/ thanks to Stanley M. Awramik, UCSB Steps towards Life 1. 2. 3. 4. synthesize biomolecules (organic C, amino acids) organize them into macromolecular systems emergence of self-replicating codes of molecules (RNA) emergence of molecular evolution via natural selection after Hazen, 2006 The Miller/Urey Experiment Stanley Miller and Harold Urey (1953) -ran experiment for one week -observed 10% of C in organic form -2% of C in amino acid form but: -too high-energy environment (lightning not continuous) -early Earth contained appreciable CO2 (in addition to CH4) on the other hand… -meteorites contain appreciable amino acids A modern-day Miller/Urey experiment Jeff Bada, Scripps Inst. of Oceanography -redid the Miller/Urey experiment in 2007 -found 22 amino acids (more than M/U!) -also analyzed the original M/U vials using modern-day analytical techniques Johnson et al., Science, 2008 “Hot volcanoe” and “cold soup” models regarding the origin of Life on Earth -organic molecules and amino acids can be organized by mineral lattices as templates Hazen, 2006 What about combining the two? hydrothermal vents A schematic of evolution of life on Earth Modified from Awramik and McNamara, in press Stromatolites: biofilms of cyanobacteria capture and bind sediment Pre-Cambrian? Today, at Shark’s Bay, Australia An Opinion • “…true consensus for life’s existence seems to be reached only with the bacterial fossils of the 1.9-billion-year-old Gunflint Formation…” Moorbath, S., 2005. Nature, 434, p. 155): . Tyler & Barghoorn, Science, 1954 Candidates for Early Archean Fossils 3.85Ga rock apatite (Ca-PO4) grain in rock Nature, 1996 “carbonaceous” remnant material after apatite dissolved with acid And the controversy continues….