Transcript Slide 1
Early Earth and the Origins of Life Why do we care? Early Earth and the Origins of Life August 25, 2009 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 4567.2±0.6 million years old Linked solidification and cooling processes Elkins-Tanton magma oceans at first… The Archean Earth System • Archean: 4.03 to 2.5 Ga • Late Heavy Bombardment (4.1 to 3.8 Ga) • Atmosphere: hardly any molecular oxygen (O2); appears at ~2Ga • UV radiation (no ozone shield) • Sun less luminous (20-30%) • Length of day ~15 hours (~584 days per year) • 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 • Magnetic field by 3.2 Ga 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 -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…. A primer for et al., 2002 ion microprobe -instrument that focuses a beam of charged ions onto the surface of a sample -charged ions generate ions for mass spectrometric analysis (separation by mass) Raman spectroscopy -instrument detects extremely small changes in energy of light/laser/IR radiation -in Schopf 2002, a laser is used to excite the sample molecules into a higher energy state; they report “Raman shifts” that denote changes in laser wavelength -shifts denote presence of specific chemical bonds and their relative orientations kerogen -concentrated, high-molecular-weight organic compounds occuring in sedimentary rocks -precursor to fossil fuels (formed upon heating of kerogen) an oil shale carbonate (X-CO3) -most commonly CaCO3, the mineral in limestone -many marine organisms form carbonate shells (corals, foraminifera) limestone cliffs C isotopes -C has two stable isotopes (12 protons, different # neutrons): 12C (99%) and 13C (1%) -for the most part, they behave identically -however, there is a slight difference in their “reactivity” -photosynthesis causes a very large shift in the relative abundance of 13C and 12C such that 12C is preferentially incorporated into biological materials cross-section of a leaf trichome -any small outgrowth or appendage on certain plants and algae trichomes on a cannabis plant chert -finely-grained, silica-rich, microcrystalline rock -is a product of high-T chemical alteration of rocks greenschist -metamorphic rocks resulting from low-T, moderate pressure environments -typically somewhat green in color